Download Projected changes in temperature and heating degree

Projected changes in temperature and
heating degree-days for Melbourne and
Victoria, 2008-2012
Updating:
“Projected changes in temperature and heating
degree-days for Melbourne, 2003-2007”
R. Suppiah and P. H. Whetton
March 2007
Undertaken for the SP-AusNet by the Climate Impacts and
Risk Group, CSIRO Marine and Atmospheric Research
II
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Projected changes in temperature and
heating degree-days for Melbourne and
Victoria, 2008-2012
Updating:
“Projected changes in temperature and heating
degree-days for Melbourne, 2003-2007”
R. Suppiah and P. H. Whetton
Climate Impacts and Risk Group, CSIRO Marine and
Atmospheric Research
March 2006
III
IV
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
ISBN: 978 1 921232 47 3
Enquiries should be addressed to:
Dr Ramasamy Suppiah
CSIRO Marine and Atmospheric Research
PMB No 1, Aspendale, Victoria 3195
Telephone (03) 9239 4554
FAX: (03) 9239 4444
E-mail: [email protected]
For copies of this report, contact:
Rob Amphlett Lewis
Manager - Distribution Regulation
SP AusNet
Level 31, 2 Southbank Boulevard
Southbank, Melbourne,
VIC 3006
Tel: 61 3 9695 6622
Facsmile: 61 3 9695 6169
Mob: 0439 311 574
Email: [email protected]
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
V
Important Notice
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VI
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Acknowledgements
The work of the authors draws upon research findings of many colleagues within the
Climate, Weather and Ocean Prediction theme of CSIRO Marine and Atmospheric
Research (CMAR), Aspendale and overseas research institutions. CSIRO global
climate and regional climate models were developed by the members of the Climate,
Weather and Ocean Prediction Theme of CMAR.
Liaison between CMAR and the SP AusNet has been facilitated by Rob Amphlett
Lewis.
Rob Amphlett Lewis (SP AusNet), Marcel LaBouchardiere (Multinet), Maurice
Amor (Multinet), Lukas Michel (SP AusNet) and Greg Meredith (Envestra) provided
useful comments on early drafts.
Ian Smith and Kevin Hennessy, both from CSIRO Marine and Atmospheric
Research also provided useful comments on the draft report.
This work was produced by CMAR under contract to SP AusNet on behalf three gas
distribution businesses (Multinet, Envestra and Sp AusNet). This work also
contributes to the CSIRO Climate research program.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
VII
EXECUTIVE SUMMARY
This report updates the previous CSIRO report on projected changes in temperature
and heating degree-days for Melbourne, 2003-2007 (Suppiah et al., 2001), which
was funded by GPU GasNet. This update presents results of a project undertaken by
CSIRO for SP AusNet on behalf of three gas distribution businesses (Multinet,
Envestra and Sp AusNet) to assess the temperature, Heating Degree days (HDDs),
and Effective Degree Days (EDDs) outlook for Melbourne and Victoria for the
period from 2008 to 2012 taking account of the observed urbanisation effect and
trends in central Melbourne temperature, and low, average and high greenhouse
warming scenarios over this period.
Observed temperature trends in Australia, Victoria and Melbourne
Australian average temperature increased by 0.89ºC (0.09ºC per decade) from 1910
to 2005. From 1950 to 2005, an accelerated increase in temperature has been
observed in Australia. Australia’s average temperature increased by 0.95ºC (0.17ºC
per decade), while the minimum increased by 1.04ºC (0.18ºC per decade) and the
maximum increased by 0.86ºC (0.15ºC per decade).
In Victoria, from 1950 to 2005, the maximum temperature increased by 0.71ºC
(0.13ºC per decade), the minimum temperature increased by 0.44ºC (0.08ºC per
decade) and the average rose by 0.58ºC (0.10ºC per decade). Greater warming was
observed from 1950 to 2005, compared with 1910 to 1950.
From 1950 to 2005, Melbourne’s maximum temperature increased by 0.81°C
(0.14°C per decade), the minimum temperature increased by 1.79°C (0.32°C per
decade) and the mean temperature increased by 1.30°C (0.23°C per decade). There
are no significant differences in increases in maximum temperatures in Victoria and
in Melbourne. However, Melbourne’s minimum temperature increase of 0.32°C per
decade is greater than that for the state.
The 11-year running means indicate that HDD has decreased from 1500 in 1950 to
below 1200 in 2005. In particular, the two lowest values were 1004 in 1988 and 1024
in 2005.
El Niño-Southern Oscillation and Victorian temperature
The relationship between the Southern Oscillation Index and Victorian mean
temperature is positive, weak in summer and autumn. None of the correlations are
statistically significant at the 95% confidence level. Therefore, variations in ENSO
don’t explain the observed trends in mean temperature in Victoria.
Contributions of urbanization and the enhanced greenhouse effect
The annual warming measured at central Melbourne from 1950 to 2005 may be due
to a number of factors, i.e. urbanization, natural variability and enhancement of the
greenhouse effect. About half of the mean warming of 0.023°C per year is due to
VIII
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
urbanization or Urban Heat Island (UHI) (0.012°C per year). The UHI shows an
annual cycle with weak contribution during June and strong contributions in April
and September.
Baseline temperatures, HDDs, and EDDs for Melbourne
In order to compute future HDDs312 and EDDs312, projected warming needs to be
added to a baseline temperature for the year 2006. Monthly baseline temperatures
have been calculated using contributions from, UHI and greenhouse warming. The
baseline temperatures for 2006 for winter and summer halves of the year, and for
annual-mean are 12.98°C, 19.28°C and 16.13°C, respectively. These estimated
baseline temperature values correspond to HDD312 values of 988.1, 180.2 and
1168.4. The annual baseline value for 2006 (16.13°C) is slightly higher than the
previous study’s (Suppiah et al., 2001) baseline value for 2000, that is 15.88°C. The
annual baseline HDD312 of the current study (1168.4) is slightly lower than the
previous baseline HDD for the year 2000 that is 1175.
Projected temperatures, HDDs, and EDDs for Melbourne
The annual increases of UHI, UHI+low greenhouse warming, UHI+average
greenhouse warming and UHI+high greenhouse warming for the years from 2007 to
2012 are 0.012°C, 0.018°C, 0.032°C and 0.038°C per year, respectively.
The estimated contribution of the combined effects of urbanization and greenhouse
warming range from 0.02 to 0.04°C in 2007 with an average warming of 0.03°C,
0.05 to 0.12°C in 2009 with an average warming of 0.09°C and 0.12°C to 0.24°C in
2012 with an average warming of 0.19°C. Table E.1 shows annual baseline
temperature for the year 2006 and projected temperatures from 2007 to 2012.
Table E.1: Annual baseline temperature (°C) for 2006 and projected
temperature for central Melbourne from 2007 to 2012.
Year
2006
2007
2008
2009
2010
2011
2012
UHI
16.13
16.14
16.16
16.17
16.18
16.20
16.21
UHI+lgw
16.13
16.15
16.16
16.18
16.20
16.22
16.24
UHI+agw
16.13
16.16
16.19
16.22
16.25
16.28
16.32
UHI+hgw
16.13
16.16
16.20
16.24
16.28
16.32
16.36
The annual changes in HDD312 for UHI, UHI+low greenhouse warming,
UHI+average greenhouse warming and UHI+high greenhouse warming for the years
from 2007 to 2012 are 0.43, 1.93, 5.78, and 8.1 HDDs312 per year. Table E.2 shows
annual baseline HDD312 for the year 2006 and projected HDDs312 from 2007 to 2012.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
IX
Table E.2: Annual baseline HDD312 for 2006 and projected HDDs312 for central
Melbourne from 2007 to 2012.
Year
2006
2007
2008
2009
2010
2011
2012
UHI
1168.4
1167.9
1167.5
1167.1
1166.7
1166.2
1165.8
UHI+lgw
1168.4
1166.5
1164.6
1162.7
1160.8
1158.8
1156.8
UHI+agw
1168.4
1163.1
1157.5
1151.9
1146.0
1139.8
1133.7
UHI+hgw
1168.4
1161.0
1153.3
1145.4
1137.2
1128.6
1119.8
The annual changes in EDD312 for UHI, UHI+low greenhouse warming,
UHI+average greenhouse warming and UHI+high greenhouse warming for the years
from 2007 to 2012 are 0.48, 2.43, 7.28, and 10.2 EDDs312 per year, respectively.
Table E.3 shows annual baseline EDD312 for the year 2006 and projected EDDs312
from 2007 to 2012.
Table E.3: Annual baseline EDD312 for 2006 and projected EDDs312 for central
Melbourne from 2007 to 2012.
Year
2006
2007
2008
2009
2010
2011
2012
UHI
1321.4
1320.9
1320.5
1320.0
1319.5
1319.0
1318.5
UHI+lgw
1321.4
1319.1
1316.7
1314.3
1311.8
1309.3
1306.8
UHI+agw
1321.4
1314.7
1307.6
1300.6
1293.1
1285.4
1277.7
UHI+hgw
1321.4
1312.1
1302.4
1292.4
1282.0
1271.2
1260.0
A comparison between projected EDDs312 for the UHI+average greenhouse warming
in the present study and by VENCorp (2006) shows good agreement in the change in
EDDs312, i.e. a decrease of 7 EDDs312 per year. However, annual decreases in
EDDs312 range from 2.43 to 10.2 between UHI+low greenhouse warming and
UHI+high greenhouse warming from 2007 and 2012. Projected temperature, HDDs
and EDDs from 2007 to 2012 do not include the contribution of natural variability.
Considering the narrow range of warming in the study period (2007-2012), it is
reasonable to choose the projected temperature, HDD312 and EDD312 derived for the
UHI+average greenhouse warming case for any short-term sensitivity analysis or
application. However, it is worth considering the UHI+low greenhouse warming
and UHI+high greenhouse warming cases for long-term planning.
X
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
XI
CONTENTS
EXECUTIVE SUMMARY ................................................................................. VII
Observed temperature trends in Australia, Victoria and Melbourne ............vii
El Niño-Southern Oscillation and Victorian temperature...............................vii
Contributions of urbanization and the enhanced greenhouse effect ...........vii
Baseline temperatures, HDDs, and EDDs for Melbourne..............................viii
Projected temperatures, HDDs, and EDDs for Melbourne ............................viii
1.
INTRODUCTION ....................................................................................... 1
2.
OBSERVED NATIONAL, VICTORIAN AND MELBOURNE
TEMPERATURE TRENDS........................................................................ 4
3.
RELATIONSHIP BETWEEN THE EL NINO-SOUTHERN
OSCILLATION AND VICTORIAN TEMPERATURE................................. 9
4.
THE MELBOURNE URBAN HEAT ISLAND INDEX, ITS VARIABILITY
AND TRENDS ......................................................................................... 12
5.
OBSERVED HEATING DEGREE DAYS AND EFFECTIVE DEGREE
DAYS IN MELBOURNE .......................................................................... 19
5.1 Heating Degree Days .................................................................... 19
5.2 Effective Degree Days................................................................... 20
5.3 Relationships between temperature, Heating Degree Days
and Effective Degree Days ........................................................... 20
5.4 Relationships among daily temperatures, HDD312 and EDD312.. 23
6.
PROJECTED TRENDS IN TEMPERATURE, HEATING DEGREE
DAYS AND EFFECTIVE DEGREE DAYS IN MELBOURNE.................. 29
6.1 Greenhouse warming and urbanization ...................................... 29
6.2 Baseline monthly temperature, heating degree days and
effective degree days.................................................................... 34
6.3 Projected monthly temperature, heating degree days and
effective degree days.................................................................... 43
6.4 Uncertainties associated with future temperature, HDD and
EDD................................................................................................. 54
6.5 A comparison between the previous CSIRO study and the
present study................................................................................. 54
7.
CONCLUSIONS ...................................................................................... 56
XII
8.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
REFERENCES ........................................................................................ 58
APPENDIX ....................................................................................................... 60
GLOSSARY OF TERMS.................................................................................. 61
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
XIII
LIST OF FIGURES
Figure 1: Spatial patterns of trends in (a) maximum, (b) minimum and (c) mean
temperatures in Australia from 1950 to 2005. Source: Australian Bureau of
Meteorology. ..................................................................................................................... 5
Figure 2: Trends and fluctuations in maximum temperatures in Victoria from 19502005. The bars indicate anomalies from the average from 1961-1990 for individual
years and the thick line is the 11-year running mean. Source: Australian Bureau of
Meteorology. ..................................................................................................................... 5
Figure 3: Same as in Figure 2, but for minimum temperatures in Victoria ........................... 6
Figure 4: Same as in Figure 2, but for mean temperatures in Victoria.................................. 6
Figure 5: Trends and fluctuations in maximum temperatures for Melbourne from 18602005. The bars indicate anomalies relative to the 1961-1990 average and the thick
line is the 11-year running mean. Source: Australian Bureau of Meteorology................ 7
Figure 6: Same as in Figure 5, but for minimum temperatures for Melbourne...................... 8
Figure 7: Same as in Figure 5, but for mean temperatures for Melbourne............................. 8
Figure 8: Relationships between seasonal SOI and Victorian mean temperature from
1950 to 2005. Significance levels for 95% and 99% are 0.264 and 0.343,
respectively MAM: March-May, JJA: June-August, SON: September to November
and DJF: December to February. .................................................................................. 10
Figure 9: Interannual variations of the seasonal SOI and mean temperature in Victoria.
The red, green and blue bars indicate temperature anomalies for El Niño, La Niña
and neutral years relative to the average for 1961-1990. The black line indicates
the SOI values. MAM: March-May, JJA: June-August, SON: September to
November and DJF: December to February. ................................................................. 11
Figure 10: (a) Interannual variations and trends in annual maximum temperature at
central Melbourne and non-urban Melbourne (gridbox) and (b) the difference
between central and non-urban Melbourne from 1950 to 2004. .................................... 13
Figure 11: (a) Interannual variations and trends in annual minimum temperature at
central Melbourne and non-urban Melbourne (gridbox), and (b) the difference
between central and non-urban Melbourne from 1950 to 2005. .................................... 14
Figure 12: (a) Interannual variations and trends in annual average temperature at
central Melbourne and non-urban Melbourne (gridbox), and (b) the difference
between central and non-urban Melbourne from 1950 to 2005. .................................... 15
Figure 13: Average monthly UHIs for Melbourne from 1950 to 2005 with their linear
trends. ............................................................................................................................. 17
Figure 14: Monthly increases in UHIs at central Melbourne. The increases are shown
as °C per decade based on trends in Figure 13.............................................................. 18
Figure 15: Heating degree days for central Melbourne (1860 to 2005). .............................. 19
Figure 16: (a) Interannual variations and trends in HDD312 and EDD312 from 1970 to
2005 in central Melbourne. (b) Linear relationship between annual HDD312 and
EDD312. Significance levels for 95% and 99% are 0.329 and 0.424, respectively.
Data source: VENCorp................................................................................................... 21
Figure 17: (a) Relationship between annual HDD312 and temperature, and (b)
relationship between annual EDD312 and temperature from 1970 to 2005.
Significance levels for 95% and 99% are 0.329 and 0.424, respectively. Data
source: VENCorp............................................................................................................ 22
Figure 18: Daily time series of averaged daily temperature and averaged cold day
temperatures at the Melbourne weather station. ............................................................ 23
Figure 19: Relationship between average daily temperature and average cold day
temperature. See Appendix for the formula. ................................................................... 24
Figure 20: (a) Relationship between average Melbourne daily temperature and HDD312
and (b) between average cold day temperature and HDD312. See Appendix for the
formula............................................................................................................................ 25
XIV
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Figure 21: (a) Relationship between average Melbourne daily temperature and EDD312
and (b) between average cold day temperature and EDD312. See Appendix fro the
formula. See Appendix for the formula. .......................................................................... 26
Figure 22: (a) Relationship between average daily EDD312 and HDD312 based on all
days from 1970 to 2005 (b) between the days which had HDD312 and EDD312
values, which vary among the days of the years. ............................................................ 27
Figure 23: (a) Daily average HHD312 and EDD312 based on the period from 1970 to
2005 and (b) average HDD312 and EDD312 based on the days which had HDD and
EDD values, which vary among the days of the years.................................................... 28
Figure 24: Anthropogenic emissions of carbon dioxide (CO2), methane (CH4), nitrous
oxide (N2O) and sulphur dioxide (SO2) for six SRES scenarios. The IS92a scenario
is also shown (from the IPCC Second Assessment Report in 1996). Source (IPCC,
2001). .............................................................................................................................. 30
Figure 25: Range (low-high) of global-average warming relative to 1990 based on the
SRES emission scenarios (IPCC, 2001).......................................................................... 31
Figure 26: Annual urban heat island (UHI) plus (low, average, high) greenhouse
warming trends for central Melbourne from 2006 to 2012 ............................................ 32
Figure 27: Monthly urban heat island (UHI) plus (Low, average, high) greenhouse
warming trends for central Melbourne from 2006 to 2012. UHI, LGW, AGW, and
HGW refer to urban heat island intensity, low, average and high greenhouse
warming, respectively ..................................................................................................... 33
Figure 28: Annual trends in monthly mean temperature at central Melbourne,
Melbourne grid box (non-urban) and Victoria based on the period from 1950 to
2005. Units are in °C per year........................................................................................ 34
Figure 29: Year-to-year variations in monthly average temperatures and their trends at
central Melbourne for the winter-half of the year from 1950 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot. ........ 35
Figure 30: Year-to-year variations in monthly average temperatures and their trends in
Victoria for the winter-half of the year from 1950 to 2005. Baseline values for the
year 2006 are also shown on the top left hand corner of each plot................................ 36
Figure 31: Year-to-year variations in monthly average temperatures and their trends at
central Melbourne for the summer-half of the year from 1950 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot. ........ 37
Figure 32: Year-to-year variations in monthly average temperatures and their trends in
Victoria for the summer-half of the year from 1950 to 2005. Baseline values for the
year 2006 are also shown on the top left hand corner of each plot................................ 38
Figure 33: Year-to-year variations in monthly heating degree days and their trends at
central Melbourne during the winter-half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot. ........ 39
Figure 34: Year-to-year variations in monthly heating degree days and their trends at
central Melbourne during the summer-half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot. ........ 40
Figure 35: Year-to-year variations in monthly effective degree days and their trends at
central Melbourne during the winter -half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot. ........ 41
Figure 36: Year-to-year variations in monthly effective degree days and their trends at
central Melbourne during the summer -half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot. ........ 42
Figure 37: Projected monthly average temperature for the winter-half of the year using
the values from Figures 27 and 29. Baseline refers to the value for the year 2006.
Uhi, lgw, agw and hgw refer to urban heat island index, and low, average and high
greenhouse warming, respectively. ................................................................................. 44
Figure 38: Projected monthly average temperature for the summer-half of the year
using the values from Figures 27 and 31. Baseline refers to the value for the year
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
XV
2006. Uhi, lgw, agw and hgw refer to urban heat island index, and low, average
and high greenhouse warming, respectively................................................................... 45
Figure 39: Projected monthly average heating degree days for the winter -half of the
year using the contributions from urbanization and greenhouse warming. Baseline
values for the year 2006 are shown at the top left hand corner of each plot. Clim,
uhi, agw and hgw refer to daily climatology from 1970-2005, and low, average and
high greenhouse warming, respectively.......................................................................... 46
Figure 40: Projected average heating degree days for winter and summer halves of the
year from 2006 to 2012. The baseline values for 2006 are also shown on the top left
hand corner of each figure. Clim, uhi, agw and hgw refer to daily climatology from
1970-2005, and low, average and high greenhouse warming, respectively................... 47
Figure 41: Projected monthly average effective degree days for the winter half of the
year for central Melbourne from 2006 to 2012. The baseline values for 2006 are
also shown on the top left hand corner of each plot. Clim, uhi, agw and hgw refer
to daily climatology from 1970-2005, and low, average and high greenhouse
warming, respectively. .................................................................................................... 48
Figure 42: Projected average effective degree days for the winter and summer halves
of the year for central Melbourne from 2006 to 2012. The baseline values for 2006
are also shown on the top left hand corner of each figure. The base line for the
winter half year is from May to October, 2006 and the baseline value for the
summer-half is from November 2005 to April 2006. Clim, uhi, agw and hgw refer to
daily climatology from 1970-2005, and low, average and high greenhouse
warming, respectively. .................................................................................................... 49
XVI
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
LIST OF TABLES
Table 1: Projected average temperature (oC) for Melbourne central for winter, summer
halves and annual from 2007 to 2012. Baseline values of monthly temperatures in 2006
were added to four cases; urban heat island (UHI) growth, UHI plus low greenhouse
warming (lgw), UHI plus average greenhouse warming (agw) and UHI plus high
greenhouse warming (hgw)............................................................................................. 51
Table 2: Projected average heating degree days (HDDs312) for Melbourne central for
winter, summer halves and annual from 2007 to 2012. Baseline values of monthly
HDDs in 2006 were added to three cases; UHI, low, average and high greenhouse
warming. Baseline values of HDDs monthly in 2006 were added to four cases; urban
heat island (UHI) growth, UHI plus low greenhouse warming (lgw), UHI plus average
greenhouse warming (agw) and UHI plus high greenhouse warming (hgw). ................ 52
Table 3: Projected average effective degree days (EDDs312) for Melbourne central for
winter, summer halves and annual from 2007 to 2012. Daily EDD312 values were
estimated using the relationship shown in Figure 22a to get monthly values. . Baseline
values of EDDs monthly in 2006 were added to four cases; urban heat island (UHI)
growth, UHI plus low greenhouse warming (lgw), UHI plus average greenhouse
warming (agw) and UHI plus high greenhouse warming (hgw). ................................... 53
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
1.
1
INTRODUCTION
This report updates the results of the previous CSIRO report on projected changes in
temperature and Heating Degree-Days (HDDs) for Melbourne, 2003-2007 (Suppiah et
al., 2001) funded by GPU GasNet. The current project is an extension of the previous
work, but funded by three gas distribution businesses (Multinet, Envestra and SP
AusNet). Although the current project’s objectives are broadly similar to the previous
one, this project includes additional information on monthly contributions by the urban
heat island (UHI) effect and greenhouse warming to Melbourne temperature over the
period 2008 to 2012. Furthermore, in the current study both HDDs312 and Effective
Degree Days (EDD312) are also calculated for the years from 2008 to 2012. The present
report aims to address the following questions:
•
What is the contribution of greenhouse warming towards mean temperature
increases in Melbourne?
•
What is the contribution of the urban heat island effect to Melbourne
temperature?
•
What are the observed trends in seasonal and annual temperature in Melbourne
as well as in Victoria?
•
What is the influence of El Niño Southern Oscillation on Victorian temperature,
if any?
•
What will be the projected temperature for Melbourne from 2008 to 2012 with
contributions from both greenhouse warming and the urban heat island effect?
•
What will be the projected HDD312 and EDD312 for Melbourne from 2008 to
2012?
•
How do the results of the present study compare with those of previous study?
Urbanization, natural climate variability and climate change due to increases in
greenhouse gases contribute to an increase in temperature in cities. Elevated
temperature in urban areas is caused by local heating due to the replacement of
vegetation by asphalt and concrete for roads, buildings, and other infrastructure
necessary to accommodate a growing population. Artificial heat is also released into the
urban atmosphere by combustive processes from vehicles, industrial activities, and
commercial and domestic air conditioning. Urban surfaces absorb more incoming solar
radiation during the day and re-radiate more heat at night compared to surrounding
vegetated surfaces (Oke, 1987). Heating of air over a city can extend up to 600 to 1500
metres above the surface during daytime, and up to 100 to 300 metres at night. The
increase in urban air temperature relative to surrounding rural temperatures is referred
to as the urban heat island effect. It is commonly measured as the difference between
urban and rural temperatures at night, when the near-surface effect is strongest.
The formation of the UHI is the result of the interaction of the following factors: (1) the
release (and reflection) of heat from industrial and domestic buildings, (2) the
2
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
absorption by concrete, brick and tarmac of heat during the day, and its release into the
lower atmosphere at night, (3) the reflection of solar radiation by glass buildings and
windows, (4) the emission of hygroscopic pollutants from cars and heavy industry act
as condensation nuclei, leading to the formation of cloud and smog, which can trap
radiation. (5) the relative absence of water in urban areas means that less energy is used
for evapotranspiration and more energy is available to heat the lower atmosphere.
Indeed, urban heat islands are often most clearly defined on calm nights.
A significant difference in minimum temperature is one of the most important contrasts
between the urban area and the surrounding rural areas. The UHI is usually measured
as the difference in minimum temperature between the urban areas and their
surrounding rural areas. The UHI is usually greatest under clear skies and light winds.
In a review of the developments in the study of urban climatology over the past two
decades, Arnfield (2003) summarised the results from empirical works of a number of
studies.
(1) UHI intensity decreases with increasing wind speed,
(2) UHI intensity decreases with increasing cloud cover,
(3) UHI intensity is greatest during anticyclonic conditions,
(4) UHI intensity is best developed in the summer or warm half of the year,
(5) UHI is greatest at night, and
(6) UHI may disappear by day or the city may be cooler than the surrounding rural
areas.
Torok et al. (2001) assessed the characteristics of urban heat islands in a number of
cities in Australia with populations ranging from approximately 1,000 to 3,000,000.
They showed a linear relationship between the maximum urban-rural temperature
difference and the logarithm of population. Australian towns and cities are likely to
have smaller maximum urban heat island effects compared to those observed in cities in
Europe and America for a given population. Melbourne is Australia’s second-largest
city, with 3.5 million people (Australian Bureau of Statistics, 2000). Morris et al.
(2001) estimated that the maximum heat island intensity for Melbourne is 1.13oC based
on 20 years data from 1972 to 1991. The maximum intensity was defined as the
difference in 6 am (local time) temperature between the CBD and the average of
Melbourne, Laverton and Moorabbin Airports. The UHI was highest in summer
(1.29oC) and lowest in winter (0.98oC).
On the basis of an analysis of the influence of synoptic circulation patterns and clouds
on the heat island effect of Melbourne, Morris et al (2001) demonstrated that the UHI is
most pronounced when the wind speed over the urban area is less than 3 m/s. On some
occasions, the UHI may be as high as 10oC when there is little or no cloud and wind
speed is less than 1.5 m/s. Simmonds and Keay (1977) found that rainfall is 10% higher
during week days than on weekends in Melbourne, and they attributed this difference to
more anthropogenic heat emissions on weekdays.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
3
Cities are also affected by global warming due to increases in greenhouse gas
concentrations. Global surface temperature data show a warming of 0.66ºC since 1901
(Jones and Moberg 2003). The past decade has witnessed 9 of the 10 warmest years on
record. Globally, there has been a warming of around 0.17ºC per decade since 1976
(IPCC, 2001). Years such as, 2005 and 2006 were also significantly warmer than
previous years (IPCC, 2007). However, there are strong spatial variations between high
and low latitudes. Importantly, these trends are based on carefully constructed and
quality controlled data sets, and excluding urban heating effects (Parker 2004).
Moreover, it is highly likely that most of the global warming observed since 1950 is due
to human activities (IPCC, 2007; Karoly and Braganza, 2005).
In this report, Chapter 2 updates trends in maximum, minimum and mean temperature
over Australia, Victoria and Melbourne from 1950 to 2005. In Chapter 3, the
relationship between the El Niño-Southern Oscillation and Victorian temperature is
assessed. Chapter 4 describes the trends and variability of the urban heat island index
(UHI) at Melbourne. Chapter 5 describes the relationship between heating degree days
and effective degree days at Melbourne. Chapter 6 describes the contribution of
urbanization and greenhouse warming to projected temperature, heating degree days
and effective degree days. Conclusions are given in Chapter 7.
4
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
2.
OBSERVED NATIONAL, VICTORIAN AND MELBOURNE
TEMPERATURE TRENDS
In Australia, the average temperature increased by 0.9°C from 1910 to 2004 (Nicholls
and Collins, 2006). Minimum temperature increased by 1.14ºC (0.12ºC per decade) and
maximum temperature increased by 0.65ºC (0.07ºC per decade).
The regional warming over the second half of the century has accelerated. For the
period 1950 to 2005, Australian average surface temperature increased by 0.95ºC
(0.17ºC per decade). Maximum temperatures increased by 0.86ºC (0.15ºC per decade)
and minimum temperatures increased by 1.04ºC (0.18ºC per decade) (BoM, 2006a).
Greater warming has been observed over southern and eastern Australia while slower
warming (and some cooling) of maximum temperatures has been observed over the
northwest and southwest regions (Figure 1a). The spatial pattern of minimum
temperature trends is very similar to that for maximum temperature trends, but the
magnitude of the trends in minimum temperature is larger over southern and eastern
Australia (see Figures 1b and 1c). The warmest year on record for Australia was 2005,
when the annual mean temperature was 1.06°C above the 1961-1990 average, the
maximum temperature was 1.21°C above average and the minimum was 0.91°C above
average (BoM 2006b).
In general, the frequency of extremely warm days and nights has increased while that of
extremely cool days and nights has decreased. From 1957 to 2004, the Australianaverage shows an increase in hot days (35oC or more) of 0.10 days/year, an increase in
warm nights (20oC or more) of 0.18 nights/year, a decrease in cool days (15oC or less)
of 0.14 days/year and a decrease in cold nights (5oC or less) of 0.15 nights/year
(Nicholls and Collins, 2006).
Temperatures in Victoria indicate a greater rate of warming after 1950 than before.
Temperature anomalies for Victoria from 1950 to 2005 are shown in Figures 2 and 3,
based on an average of twelve stations across the State. The 1961-1990 average values
are also shown in these figures. From 1950 to 2005, the maximum temperature
increased by 0.71ºC (0.13ºC per decade), the minimum temperature increased by 0.44ºC
(0.08ºC per decade) and the average temperatures rose by 0.58ºC (0.10ºC per decade),
which is slightly more than that seen over the period from 1950 to 2000 (Suppiah et al,
2001). Recent above average values in maximum and below normal values in minimum
temperature in winter were associated with drier conditions in the State, a typical
example being winter 2006. These conditions lead to increased frost frequency.
Moreover, state-wide average temperatures from 1950 to 2005 based on rural stations
show broad-scale variations due to natural variability and greenhouse warming, since
we assume urbanization effects are negligible in rural areas.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
(a)
5
(b)
Trend in Minimum Temperature
1950-2005 (oC/10yrs)
Trend in Maximum Temperature
1950-2005 (oC/10yrs)
(c)
Trend in Mean Temperature
1950-2005 (oC/10yrs)
Figure 1: Spatial patterns of trends in (a) maximum, (b) minimum and (c) mean
temperatures in Australia from 1950 to 2005. Source: Australian Bureau of
Meteorology.
1.6
1.4
Temperature anomalies (oC)
1.2
1.0
Maximum temperature
Average 1961-90: 19.86 (oC)
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
1950
1960
1970
1980
1990
2000
2010
Year
Figure 2: Trends and fluctuations in maximum temperatures in Victoria from 19502005. The bars indicate anomalies from the average from 1961-1990 for individual
years and the thick line is the 11-year running mean. Source: Australian Bureau of
Meteorology.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
6
1.6
1.4
Temperature anomalies (oC)
1.2
1.0
Minimum temperature
Average 1961-90: 8.34 (oC)
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
1950
1960
1970
1980
1990
2000
2010
Year
Figure 3: Same as in Figure 2, but for minimum temperatures in Victoria
1.6
1.4
Temperature anomalies (oC)
1.2
1.0
Mean temperature
Average 1961-90: 14.10 (oC)
0.8
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
1950
1960
1970
1980
1990
2000
2010
Year
Figure 4: Same as in Figure 2, but for mean temperatures in Victoria.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
7
Maximum temperature at central Melbourne station increased steadily from 1890 to
1940 and from 1970 to 2005, with small decreases in 1940s and 1960s. In particular,
the years from 1997 to 2005 show large increases, with 2005 being the warmest year
on record (Figure 5). Maximum temperature anomalies also show strong interannual
variations. Unlike maximum temperature, minimum temperatures in Figure 6 show a
steady increase from 1860 to 1920 and from 1950 to 2005, with a slight decrease from
1920 to 1950. Consequently, Melbourne’s mean temperature anomalies in Figure 7
show a slow increase from 1890 to 1940 and a rapid increase from 1950 to present.
From 1950 to 2005, Melbourne’s maximum temperature increased by 0.81°C (0.14°C
per decade), the minimum temperature increased by 1.79°C (0.32°C per decade) and the
mean temperature increased by 1.30°C (0.23°C per decade).
It is interesting to note that increases in maximum temperatures in Victoria and in
Melbourne are not significantly different. However, minimum temperatures show
significant differences due to the influence of urbanization. In particular, the Melbourne
minimum temperature increase of 0.32°C per decade is greater than that averaged over
the State. More detail on temperature at the Melbourne weather station and rural
temperatures surrounding the CBD is given later.
2.0
o
Temperature anomalies ( C)
1.5
Maximum temperature
Average 1961-1990 = 19.95 oC
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
1860
1880
1900
1920
1940
1960
1980
2000
Year
Figure 5: Trends and fluctuations in maximum temperatures for Melbourne from 18602005. The bars indicate anomalies relative to the 1961-1990 average and the thick line
is the 11-year running mean. Source: Australian Bureau of Meteorology.
8
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
1.5
Minimum temperature
Average 1961-1990 = 10.99 oC
0.5
o
Temperature anomalies ( C)
1.0
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
1860
1880
1900
1920
1940
1960
1980
2000
Year
Figure 6: Same as in Figure 5, but for minimum temperatures for Melbourne.
1.5
Mean temperature
o
Temperature anomalies ( C)
1.0
Average 1961-1990 = 15.47 oC
0.5
0.0
-0.5
-1.0
-1.5
-2.0
1860
1880
1900
1920
1940
1960
1980
2000
Year
Figure 7: Same as in Figure 5, but for mean temperatures for Melbourne.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
3.
9
RELATIONSHIP BETWEEN THE EL NIÑO-SOUTHERN
OSCILLATION AND VICTORIAN TEMPERATURE
The temperature variations described in the previous chapter may be caused by a
number of factors. One of the most well-known factors affecting climate variability of
Australia is the El Niño Southern Oscillation (ENSO), which represents the difference
between the Indonesian low pressure region and the South Pacific subtropical high
pressure region. El Niño events are associated with higher sea surface temperatures in
the central and eastern Pacific Ocean, weaker trade winds (easterlies) and are often
preceded by westerly wind bursts along the equator. El Niño events are also associated
with higher than normal pressure in the Indonesian-north Australian region and lower
than normal in the central Pacific. La Niña events have the opposite characteristics to El
Niño events. The Southern Oscillation Index (SOI) is the difference in mean sea-level
pressure between Darwin and Tahiti. Positive SOI values tend to correspond to La Niña
events and negative values to El Niño events.
The ENSO phenomenon is the largest single factor affecting the year-to-year variability
of climate in the tropics and some parts of the mid-latitudes. El Niño events produce
below normal rainfall, and often drought, over much of northern and eastern Australia.
The influence of ENSO on Australian temperature is more complex than rainfall. On
one hand, positive SOI can lead to higher temperatures prior to the rainy season, but
excessive rainfall can lead to a significant cooling of the surface. Droughts that are
associated with negative SOI also lead to higher temperatures. Therefore, the influence
of ENSO has strong seasonal dependencies. The relationship between Australian
maximum and minimum temperature and the SOI (Jones and Trewin, 2000) is strong
over north and eastern Australia, but weak over southern Australia.
Figure 8 shows that the relationship between the SOI and Victorian mean temperature is
positive, but weak in summer and autumn. The relationship during winter and spring is
negative and weak. None of the correlations are statistical significant at the 95%
confidence level. Figure 9 shows seasonal values of the SOI and Victorian mean
temperature from 1950 to 2005. In this figure, El Niño, La Niña and neutral years are
marked. Most of the El Niño years are associated with negative temperature anomalies
in autumn and summer, while La Niña years are associated with positive and negative
temperature anomalies. In winter and spring there is no clear link between El Niño/La
Niña and temperature anomalies. The weak relationship between ENSO and Victorian
temperatures means that ENSO can’t explain much of the observed temperature
variability from 1950-2005.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
10
1.5
1.0
MAM
r=0.239
0.5
0.0
-0.5
-1.0
-1.5
1.5
JJA
1.0
r= -0.091
0.5
Temperature anomalies (oC)
0.0
-0.5
-1.0
1.5
1.0
SON
r= -0.111
0.5
0.0
-0.5
-1.0
-1.5
-2.0
2.5
2.0
DJF
1.5
r=0.254
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-35 -30 -25 -20 -15 -10 -5
0
5
10 15 20 25
SOI
Figure 8: Relationships between seasonal SOI and Victorian mean temperature from
1950 to 2005. Significance levels for 95% and 99% are 0.264 and 0.343, respectively
MAM: March-May, JJA: June-August, SON: September to November and DJF:
December to February.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
20
MAM
11
1.6
10
0.8
0
0.0
-0.8
-10
-1.6
-20
-2.4
JJA
1.6
Southern Oscillation Index
20
10
0.8
0
0.0
-10
-0.8
-20
-30
30
-1.6
SON
2.4
20
1.6
10
0.8
0
0.0
-0.8
-10
-1.6
-20
30
Temperature anomalies (oC)
-30
30
-2.4
DJF
2.4
20
1.6
10
0.8
0
0.0
-10
-0.8
-1.6
-20
-30
1950
-2.4
1960
1970
1980
1990
2000
2010
Year
Figure 9: Interannual variations of the seasonal SOI and mean temperature in Victoria.
The red, green and blue bars indicate temperature anomalies for El Niño, La Niña and
neutral years relative to the average for 1961-1990. The black line indicates the SOI
values. MAM: March-May, JJA: June-August, SON: September to November and DJF:
December to February.
12
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
4.
THE MELBOURNE URBAN HEAT ISLAND INDEX, ITS
VARIABILITY AND TRENDS
Quality controlled daily maximum and minimum temperature data used in this study
were provided by the National Climate Centre (NCC) of the Bureau of Meteorology.
Stations used to create the gridded temperature data have been checked for
homogeneity. Changes in the locations of stations, observing practices, conversion of
temperature records to the metric system, urban influences on temperature and
discontinuities in records have been checked. Annual-average data for central
Melbourne for the period 1860 to 2000 include urbanization effects.
In addition, monthly average temperatures on a grid covering Australia (resolution of 25
km) were also provided by the NCC for the period 1950 to 2004. Some of the details of
the high-quality temperature data are described by Della-Marta et al. (2004). This
gridded data set is based on rural observations only, and therefore excludes urbanization
effects on temperature in major cities.
The procedure for calculating the UHI is described by Suppiah et al. (2001).
Essentially, temperatures from the grid box representing Melbourne are used to
represent rural temperatures surrounding the city. This gridded data set has no urban
influence since it is interpolated from surrounding rural stations, so it effectively
provides us a non-urbanised Melbourne temperature record. A comparison of the 19502005 grid box data for Melbourne with data from the Melbourne weather station
provides an estimate of the magnitude of the Melbourne trend due to urbanization.
Figures 10a and b show interannual variations and trends in annual maximum
temperatures for central Melbourne, non-urban Melbourne and the differences between
them. It is evident in Figure 10 (a) that temperatures at both central and non-urban
Melbourne increased from 1950 to 2005. However, there are decadal-scale variations
which determine the differences in Figure 10b. Both time series show slow increases
due to long-term variations. Central Melbourne maximum temperatures increased by
0.81°C (0.14°C per decade) and non-urban temperatures increased by 0.68°C (0.12°C
per decade) during this period. The difference was strong during the 1950s and from the
1990s, but weak from the 1960s to the 1980s. The trend in the difference is 0.023°C per
decade. However, an abrupt change in the minimum temperature difference around
1965 suggests a possible change in conditions around the Melbourne weather station
(and thus a change that need not be part of a general urbanisation trend). An
examination of relevant metadata and discussion with the Bureau of Meteorology (B.
Trewin, personal communication) failed to identify a clear cause of the change around
1965.
Figure 11 shows interannual variations and trends in annual minimum temperatures for
central Melbourne, non-urban Melbourne and the differences between them, Clearly,
central Melbourne minimum temperatures increase more strongly than the non-urban
minimum temperatures. The former increased by 1.79°C (0.32°C per decade) and the
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
13
latter increased by only 0.58 (0.10°C per decade). The trend in the difference from 1950
to 2004 is 1.21°C (0.22°C per decade).
22.0
21.5
Temperature (oC)
21.0
Annual Maximum
(a)
Melbourne City
Melbourne gridbox
Linear trends
20.5
20.0
19.5
19.0
18.5
18.0
17.5
1950
1960
1970
1980
1990
2000
2010
Year
2.0
1.9
1.8
1.7
Temperature (oC)
1.6
(b)
Annual Maximum
Melbourne City minus Gridbox
Linear trend
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
1950
1960
1970
1980
1990
2000
2010
Year
Figure 10: (a) Interannual variations and trends in annual maximum temperature at
central Melbourne and non-urban Melbourne (gridbox) and (b) the difference between
central and non-urban Melbourne from 1950 to 2004.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
14
12.5
12.0
Temperature (oC)
11.5
Annual Minimum
(a)
Melbourne City
Melbourne gridbox
Linear trends
11.0
10.5
10.0
9.5
9.0
8.5
1950
1960
1970
1980
1990
2000
2010
Year
2.0
1.8
Temperature (oC)
1.6
(b)
Annual Minimum
Melbourne City minus Gridbox
Linear trend
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1950
1960
1970
1980
1990
2000
2010
Year
Figure 11: (a) Interannual variations and trends in annual minimum temperature at
central Melbourne and non-urban Melbourne (gridbox), and (b) the difference between
central and non-urban Melbourne from 1950 to 2005.
Interannual variations and trends in annual average temperature at both central and nonurban Melbourne are shown in Figures 12 a while their difference is shown in Figure
12b. Annual average temperatures from 1950 to 2005 increased by 1.30°C (0.23°C per
decade) at central Melbourne and by 0.63°C (0.11°C per decade) for non-urban
Melbourne. The average temperature difference between central and non-urban
Melbourne increased by 0.66°C (0.12°C per decade).
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
17.0
16.5
15
(a)
Annual Average
Melbourne City
Melbourne gridbox
Linear trends
Temperature (oC)
16.0
15.5
15.0
14.5
14.0
13.5
1950
1960
1970
1980
1990
2000
2010
Year
2.0
1.9
1.8
1.7
Temperature (oC)
1.6
(b)
Annual Average
Melbourne City minus Gridbox
Linear trend
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
1950
1960
1970
1980
1990
2000
2010
Year
Figure 12: (a) Interannual variations and trends in annual average temperature at
central Melbourne and non-urban Melbourne (gridbox), and (b) the difference between
central and non-urban Melbourne from 1950 to 2005.
The net effect of urbanization on mean temperatures is a city-rural difference of
+0.69°C in 1950, increasing to about +1.36°C in 2005. The effect of urbanization
appears most evident in minimum temperature. The net effect on minimum temperature
is a city-rural difference of +0.40°C in 1950, increasing to about +1.61°C by 2005, an
increase of about 1.21°C over 56 years. The difference in mean minimum temperature
is about 1.21°C, which is very close to the 1971-1991 value of 1.13°C found by Morris
et al. (2001), but lower than the estimate given in the previous CSIRO study (Suppiah et
al. 2001). The difference in the estimate of the increase in minimum temperature could
arise for two reasons. (1) In the previous study, we used 100km resolution gridded data
but in the present study we used 25 km resolution gridded data; (2) The previous
estimate was based on the period from 1965 to 2000, while the present study extends to
2005. Although we have used data from 1950 to 2005 instead of 1965 to 2005, we have
16
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
no obvious reason to omit the years before 1965 in this analysis. Moreover, VENCorp
(2003) also reported that Melbourne weather station temperatures prove to be
statistically better predictors of gas system demand than data from alternative sources
such as Tullamarine, Sale and Laverton.
Monthly UHIs are shown in Figure 13. The left hand panels indicate the UHIs for the
winter-half of the year, while the right-hand panels show the UHIs for the summer-half
year. The increase in UHI is small in June and large in September. High cloud amount
and low sunshine hours in June and strong ventilation in September are major factors
for such low and high UHIs in these months. The trends in the UHIs also show a clear
annual cycle with a minimum in winter and some months in summer and a maximum in
autumn and spring, as shown in Figure 14. In this analysis, we found that the UHI is
strong during autumn and spring and weak particularly in June and July. The results
derived from monthly values show good agreement in with the winter results of Morris
et al. (2001), who found low UHI in winter, but the results for summer derived from
this analyse differ to their results.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
2.5
2.0
Mean temperature
2.5
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
2.5
0.0
2.5
June
2.0
1.5
1.0
1.0
0.5
0.5
0.0
2.5
0.0
2.5
July
1.5
1.0
1.0
0.5
0.5
0.0
2.5
0.0
2.5
2.0
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
2.5
0.0
2.5
September
2.0
1.5
1.0
1.0
0.5
0.5
0.0
2.5
0.0
2.5
October
January
February
March
2.0
1.5
2.0
December
2.0
1.5
August
November
2.0
1.5
2.0
Temperature difference (oC)
May
17
April
2.0
1.5
1.5
1.0
1.0
0.5
0.5
0.0
0.0
1940 1950 1960 1970 1980 1990 2000 2010 1940 1950 1960 1970 1980 1990 2000 2010
Year
Year
Figure 13: Average monthly UHIs for Melbourne from 1950 to 2005 with their linear
trends.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
18
0.25
o
UHI ( C) per decade
0.20
0.15
0.10
0.05
0.00
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Months
Figure 14: Monthly increases in UHIs at central Melbourne. The increases are shown
as °C per decade based on trends in Figure 13.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
19
5.
OBSERVED HEATING DEGREE DAYS AND EFFECTIVE
DEGREE DAYS IN MELBOURNE
5.1
Heating Degree Days
Heating degree days (HDD) are calculated using daily temperature data. It is an index to
estimate the amount of energy required for heating during the winter or cool season.
18°C represents a threshold temperature for residential gas heating and this is a fairly
common industry standard internationally (VENCorp, 2006). When the daily
temperature drops below 18.0°C, most business and residential buildings require heat to
maintain a comfortable interior temperature. A threshold value of 18.0°C is used to
calculate the HDD and the formula for calculation follows the conditions given below:
When the average daily temperature is above 18.0°C, then the HDD total is zero. If the
average daily temperature is below 18.0°C, the HDD amount is the difference between
18.0°C and the average daily temperature. Daily HDD values are added and monthly
and annual values are obtained.
Annual HDD values for central Melbourne from 1860 to 2005 are shown in Figure 15
along with their long-term trends. It is evident that there is strong interannual variability
but a steady decrease from 1950 to 2005. The 11-year running means indicate that
HDD has decreased from 1500 in 1950 to below 1200 in 2005. In particular, the two
lowest values were 1004 in 1988 and 1024 in 2005.
1800
1700
Heating Degree-Days
1600
1500
1400
1300
1200
1100
1000
900
1860
HDD- actual values
11-year running mean
1880
1900
1920
1940
1960
1980
2000
Year
Figure 15: Heating degree days for central Melbourne (1860 to 2005).
20
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
5.2
Effective Degree Days
Comfort in buildings and associated energy demand are also affected by sunshine hours,
wind speed (the chill factor) and relative humidity. VENCorp (2003, page 6) derived an
index for Melbourne, called Effective Degree Days (EDDs), based on these variables
and a seasonal factor, which provides a better predictor for gas demand. VENCorp
(2003) derived EDD66 which represents the average of eight three-hourly observations of
Melbourne temperature and wind, with 50% weighting applied to the 6am observations
(which tend to be coldest). In a subsequent study, VENCorp (2006) derived alternative
EDD indices that include EDD63, EDD33, EDD129 and EDD312. EDD63 represents 6am
current calendar day to 3am of the following calendar day with equal weightings on all
temperature and wind observations. EDD33 represents 3am current calendar day to 3am
of the following calendar day with 50% weightings on all temperature and wind
observations. EDD129 represents 12am to 9pm of the current calendar day with equal
weightings on all temperature and wind observations. EDD312 represents 3am to 12am
midnight with equal weightings on all temperature and wind observations. Based on a
comparison among various EDD indices, VENCorp (2006) suggested that the EDD312
index is the best predictor of 6am gas day (and 6am peak day) heating demand, and the
EDD66 is the poorest predictor. EDD33 and the EDD129 indices are slightly inferior to the
EDD312 index. Therefore, we have used temperature and EDD312 indices of VENCorp
(2006) in this analysis. Daily EDD values from 1970 to 2006 were calculated by
VENCorp using the formula given in VENCorp (2003). This data set was made
available to CSIRO though SP AusNet. Further information on this data set is available
in: http://www.vencorp.com.au/docs/consultations/EDD_History_Data. In this website,
3-hourly temperature data for Melbourne weather station are available.
5.3
Relationships between temperature, Heating Degree
Days and Effective Degree Days
We investigated the relationship between HDD312, which is based on daily temperature,
and EDD312 to see wether they are strongly correlated.. This allowed us to construct a
simple relationship between daily HDD and EDD that can be used to project future
seasonal and annual EDDs from the temperature-based HDD as temperature shows
strong relationship with HDD and EDD. Figure 16a shows the variation in annual
HDD312 and EDD312 from 1970 to 2005 and their linear trends, while Figure 16b shows
the linear relationship between HDD312 and EDD312. It is evident that both HDD312 and
EDD312 show a negative trend from 1970 to 2005 and strong year-to-year variations.
The period from 1970 to 2005 also shows an increasing trend in temperature in central
Melbourne in Figure 12a.
We established a relationship between annual temperature and HDD312 and also
between annual temperature and EDD312 in central Melbourne. The relationship
between annual temperatures and HDD312 (Figure 17a) and between temperature and
EDD312 (Figure 17b) is very strong and similar to that shown by VENCorp (2006). The
correlation between temperature and EDD312 is slightly weaker (r=0.734) than between
temperature and HDD312 (r=0.886), but they are both statistically significant at the 99%
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
21
level. The slightly weaker correlation for EDD312 indicates the importance of factors
other than temperature. Since the other factors have a relatively minor effect on
calculated EDD312, we use the relationship between daily temperature and both HDD312
and EDD312 to project HDD and EDD for the years 2008-2012.
1800
(a)
1700
1600
EDD/HDD
1500
1400
1300
1200
1100
HDD
EDD
Linear trend
1000
900
1970
1980
1990
2000
2010
Year
1800
(b)
1700
EDD
1600
1500
1400
1300
HDD vs EDD
Linear trend
1200
r=0.898
1100
1000
1100
1200
1300
1400
1500
HDD
Figure 16: (a) Interannual variations and trends in HDD312 and EDD312 from 1970 to
2005 in central Melbourne. (b) Linear relationship between annual HDD312 and EDD312.
Significance levels for 95% and 99% are 0.329 and 0.424, respectively. Data source:
VENCorp.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
22
1500
(a)
1400
HDD
1300
1200
HDD vs temperature
Linear trend
1100
r=0.886
1000
14.8
15.0
15.2
15.4
15.6
15.8
16.0
16.2
16.4
16.6
16.8
o
Temperature ( C)
1800
(b)
1700
EDD
1600
1500
1400
1300
EDD vs temperature
Linear trend
r=0.734
1200
1100
14.8
15.0
15.2
15.4
15.6
15.8
16.0
16.2
16.4
16.6
16.8
o
Temperature ( C)
Figure 17: (a) Relationship between annual HDD312 and temperature, and (b)
relationship between annual EDD312 and temperature from 1970 to 2005. Significance
levels for 95% and 99% are 0.329 and 0.424, respectively. Data source: VENCorp.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
5.4
23
Relationships among daily temperatures, HDD312 and
EDD312.
In this section, we establish a relationship between temperature, HDD312 and EDD312 in
order to estimate future HDD312 and EDD312 using projected temperature. The
relationships are based on observed data from the period 1970 to 2005. Daily data were
obtained from VENCorp. We used two types of daily temperature data:
(1) Daily temperature (DT) data averaged from for each day (January 1 to
December 31) from 1970 to 2005. These values range from 9 to 22°C.
(2) Cold day temperatures (CDT) which are defined as the days below 18°C.
o
Temperature ( C)
It is clear from Figure 18 that average daily temperatures and cold day temperatures for
central Melbourne do not differ in winter but, are very different during summer and
autumn. The relationship between average daily temperature and average cold day
temperature is very strong below 13°C - these values are found between May and
September. The variability is strong above 13°C.
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
Daily temperature
Cold day temperature
1
32
60
91
121 152 182 213 244 274 305 335 365
Days from January 1
Figure 18: Daily time series of averaged daily temperature and averaged cold day
temperatures at the Melbourne weather station.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
24
18
16
o
Cold day temperature ( C)
17
15
14
13
12
11
CDT vs DT
2nd order polynomial
10
9
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Daily temperature (oC)
Figure 19: Relationship between average daily temperature and average cold day
temperature. See Appendix for the formula.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
25
The negative relationship between HDD312 and daily temperature for central Melbourne
is very strong and linear below 18°C, but weak above that threshold level, as shown in
Figure 20. There is a strong relationship between daily temperature and HDD312.
9
(a)
8
7
6
HDD
5
4
3
2
1
DT vs HDD
3rd order polynomial
0
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Daily temperature (oC)
9
(b)
8
7
HDD
6
5
4
3
2
CDT vs HDD
Linear regression
1
0
9
10
11
12
13
14
15
16
17
18
o
Cold day temperature ( C)
Figure 20: (a) Relationship between average Melbourne daily temperature and HDD312
and (b) between average cold day temperature and HDD312. See Appendix for the
formula.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
26
The relationships between daily temperature and EDD312 and between cold day
temperature and EDD312 are shown in Figures 21a and b. The negative relationship is
strong and linear between 10 to 16°C, but non-linear above 16°C. This indicates the
importance of meteorological factors other than temperature.
13
12
(a)
11
10
9
EDD
8
7
6
5
4
3
2
EDD vs DT
2nd order polynomial
1
0
-1
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23
Daily temperature (oC)
12
(b)
11
10
9
8
EDD
7
6
5
4
3
2
EDD vs CDT
3rd order polynomial
1
0
9
10
11
12
13
14
15
16
17
18
o
Cold day temperature ( C)
Figure 21: (a) Relationship between average Melbourne daily temperature and EDD312
and (b) between average cold day temperature and EDD312. See Appendix fro the
formula. See Appendix for the formula.
The relationship between daily average HDD312 and EDD312 from 1970 to 2005 is
shown in Figure 22a, and the relationship between the days, which had HDD and EDD
values during the period from 1970 to 2005 is shown in Figure 22b. Averaged daily
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
27
HDD and EDD based on 1970 to 2005 are shown in Figure 23a and average daily
values based on days, which had HDD and EDD values are shown in Figure 23b. In
both cases, there is a strong relationship. However, there are some outliers in Figure
22b, compared to the Figure 22a. These exceptionally cold days are recorded in
February as seen in Figure 23b.
The strong relationships between daily temperatures, HDDs and EDDs will be used to
estimate future HDDs and EDDs using projected average temperature due to
urbanization and greenhouse warming for years 2008 to 2012.
12
(a)
11
10
9
8
EDD
7
6
5
4
3
2
EDD vs HDD
3rd order polynomial
1
0
0
1
2
3
4
5
6
7
8
9
HDD
12
(b)
11
10
9
8
EDD
7
6
5
4
3
2
EDD vs HDD
3rd order polynomial
1
0
0
1
2
3
4
5
6
7
8
9
HDD
Figure 22: (a) Relationship between average daily EDD312 and HDD312 based on all
days from 1970 to 2005 (b) between the days which had HDD312 and EDD312 values,
which vary among the days of the years.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
28
14
(a)
HDD
EDD
12
HDD/EDD
10
8
6
4
2
0
1
32
60
91
121
152
182
213
244
274
305
335
365
Days from January 1
14
(b)
HDD
EDD
12
HDD/EDD
10
8
6
4
2
0
1
32
60
91
121
152
182
213
244
274
305
335
365
Days from January 1
Figure 23: (a) Daily average HHD312 and EDD312 based on the period from 1970 to
2005 and (b) average HDD312 and EDD312 based on the days which had HDD and
EDD values, which vary among the days of the years.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
29
6.
PROJECTED TRENDS IN TEMPERATURE, HEATING
DEGREE DAYS AND EFFECTIVE DEGREE DAYS IN
MELBOURNE
6.1
Greenhouse warming and urbanization
To estimate future climate change, scientists develop scenarios. These are not forecasts
or predictions of what will actually happen. They allow analysis of “what if?” questions
based on various assumptions about human behaviour, economic growth and
technological change.
One set of IPCC scenarios assume “business as usual” without explicit policies to limit
greenhouse gas emissions, although some scenarios include other environmental
policies that indirectly affect greenhouse gases. These are described in the Special
Report on Emission Scenarios (SRES, 2000). Other IPCC scenarios include actions to
reduce carbon dioxide (CO2) emissions and stabilize CO2 concentrations at some level
above the current value of 380 ppm. These stabilization scenarios would postpone or
avoid some of the more serious damages associated with higher rates of warming.
Probabilities have not been assigned to any of the scenarios. The global warming
projections described below are used in the development of regional climate change
projections for Australia, so it is important to understand the basis of the global
warming projections.
The SRES (2000) scenarios represent a broad range of the main demographic, economic
and technological driving forces of greenhouse gas and sulphur emissions for the 21st
century. The Terms of Reference for the scenarios required that they did not include
additional climate initiatives that explicitly assume implementation of the United
Nations Framework Convention on Climate Change (UNFCCC) or the emission targets
of the Kyoto Protocol. Each of the 40 SRES scenarios represents a variation within one
of four 'storylines': A1, A2, B1 and B2.
• A1 describes a world of very rapid economic growth in which the population peaks
around 2050 and declines thereafter and there is rapid introduction of new and more
efficient technologies. The three sub-groups of A1 are fossil fuel intensive (A1FI),
non-fossil fuel using (A1T), and balanced across all energy sources (A1B).
• A2 depicts a world of regional self-reliance and preservation of local culture. In A2,
fertility patterns across regions converge slowly, leading to a steadily increasing
population and per capita economic growth and technological change is slower and
more fragmented slower than for the other storylines.
• B1 describes a convergent world with the same population as in A1, but with an
emphasis on global solutions to economic, social and environmental sustainability,
including the introduction of clean, efficient technologies.
• B2 places emphasis on local solutions to economic, social and environmental
sustainability. The population increases more slowly than that in A2. Compared
with A1 and B1, economic development is intermediate and less rapid, and
technological change is more diverse.
30
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Figure 24 shows the SRES (2000) anthropogenic (human-induced) emission scenarios
for carbon dioxide, methane, nitrous oxide and sulphur dioxide. Carbon cycle models
are used to convert emissions into well-mixed atmospheric concentrations, allowing for
uptake of emissions by the land and ocean, land and ocean climate feedbacks, and
chemical reactions in the atmosphere. By the year 2100, carbon cycle models give
estimates of atmospheric CO2 concentrations ranging from 540 to 970 ppm (an increase
of 44 to 159% relative to 380 ppm in the year 2005). Methane concentrations are
projected to change by -11 to +112% and nitrous oxide concentrations may rise 12 to
46%. Concentrations of tropospheric ozone, hydrofluorocarbons and perfluorocarbons
are also projected to increase. The SRES (2000) scenarios include the possibility of
increases or decreases in anthropogenic aerosols (e.g. black carbon, sulphate aerosols,
biomass aerosols and organic carbon aerosols) depending on the extent of fossil fuels
use. All SRES scenarios give positive forcing for the well-mixed greenhouse gases,
except for methane in the B1 scenario by the year 2100.
Figure 24: Anthropogenic emissions of carbon dioxide (CO2), methane (CH4), nitrous
oxide (N2O) and sulphur dioxide (SO2) for six SRES scenarios. The IS92a scenario is
also shown (from the IPCC Second Assessment Report in 1996). Source (IPCC, 2001).
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
31
In the following section, we discuss how we estimate the average temperature at
Melbourne from 2006 to 2012 considering the effects of both urbanization and
greenhouse warming. The range of greenhouse warming for 2006 to 2012 is based on
scenarios in Figure 24 and CSIRO’s (2001) regional warming projections for Australia.
Temperature projections were constructed using the SRES emission scenarios: Special
Report on Emission Scenarios (SRES), published by the IPCC. Uncertainties
associated with the range of future emission scenarios, range of global responses of
climate models, and model-to-model differences in the regional climate change pattern
are considered when producing these temperature projections. The range of warming
from 1990 to 2100 in Figure 25 allows for the full range of SRES (2000) greenhouse
gas and sulfate aerosol emission scenarios. The greenhouse warming is relatively small
until 2020, but accelerates faster after 2020. The range in global warming also shows
large range after 2020. In this report, projected temperature values for uhi+low
greenhouse warming, uhi+average greenhouse warming and uhi+high greenhouse
warming are associated with low (B1, green curve), mid (A2, yellow curve) and high
(A1FI, dashed red curve) global warming scenarios. Moreover, the warming associated
with the A2 scenario follows the mid-range or average warming in the future. Further
details of the methodology and projected temperature for States and Territories and also
for the whole of Australia are given in Whetton et al. (2005). Climate change
projections indicate a warming of 0.01 to 0.03°C for Melbourne by the year 2007 and
0.03 to 0.17°C by 2012 relative to 2006. We assume that warming observed in
Melbourne up to 2006 includes the effects of urbanization, natural variability and
greenhouse warming.
Figure 25: Range (low-high) of global-average warming relative to 1990 based on the
SRES emission scenarios (IPCC, 2001)
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
32
It is highly likely that urbanization effects will increase with the growth of population.
The population of Melbourne was 3.52 million is 2002 and it is projected to increase to
4.19 million by 2021 and to 5.56 million by 2051 (Australian Bureau of Statistics,
2002). Based on the increase in population and an increase in minimum temperature at
Melbourne, it is assumed that the urbanization effect on mean temperature will continue
to increase at the current rate at least until 2012. The annual warming at central
Melbourne from 1950 to 2005 due to the combined effects of urbanization, natural
variability and greenhouse effect is estimated to be +0.022°C per year, in which
0.012°C per year (see Figure 11) is contributed by urbanization. Since there is little
evidence of the effect of urbanization on maximum temperature, the contribution is
mainly from the increase in minimum temperature. Therefore, we have added the
annual warming due to urbanization (0.012°C per year) to projected greenhouse
warming (quantified above) to project the total warming to from 2006 to 2012. Figure
26 shows the contribution of urbanization and greenhouse warming, relative to 2006.
The estimated contribution of urbanization and greenhouse warming is 0.02to 0.04°C in
2007 with an average warming of 0.03°C, 0.05 to 0.12°C in 2009 with an average
warming of 0.09°C and 0.12°C to 0.24°C in 2012 with an average warming of 0.19°C.
In this study, We have added the annual low, average and high greenhouse warming to
monthly UHI to estimate the monthly projected average temperature for Melbourne.
Figure 27 shows projected monthly temperature increases due to combined affects of
urbanization and low, average and high greenhouse warming. The contribution from
low, average and high global warming are same for all months and variations in
warming among the months are due to variations in UHI as shown in Figures 13 and 14.
0.30
Temperature (oC)
0.25
0.20
Urbanisation (UHI)
Low greenhouse warming +UHI
Average greenhouse warming +UHI
High greenhouse warming + UHI
0.15
0.10
0.05
0.00
2006
2007
2008
2009
2010
2011
2012
Year
Figure 26: Annual urban heat island (UHI) plus (low, average, high) greenhouse
warming trends for central Melbourne from 2006 to 2012
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
0.3
May
0.3
November
0.2
0.2
0.1
0.1
0.0
0.3
0.0
0.3
December
June
0.2
0.2
0.1
0.1
0.0
0.3
0.0
0.3
o
Temperature difference ( C)
July
January
0.2
0.2
0.1
0.1
0.0
0.3
0.0
0.3
August
February
0.2
0.2
0.1
0.1
0.0
0.3
0.0
0.3
March
September
0.2
0.2
0.1
0.1
0.0
0.3
0.0
0.3
0.2
UHI
UHI+LGW
UHI+AGW
UHI+HGW
33
April
October
0.2
0.1
0.1
0.0
0.0
2006 2007 2008 2009 2010 2011 2012 2006 2007 2008 2009 2010 2011 2012
Year
Year
Figure 27: Monthly urban heat island (UHI) plus (Low, average, high) greenhouse
warming trends for central Melbourne from 2006 to 2012. UHI, LGW, AGW, and HGW
refer to urban heat island intensity, low, average and high greenhouse warming,
respectively
34
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
6.2
Baseline monthly temperature, heating degree days and
effective degree days
To estimate monthly baseline values for 2006, we fitted linear trend lines for average
temperature. Increases in average temperatures are stronger in central Melbourne
compared to non-urban Melbourne and Victoria, as is clearly evident in Figure 28.
Months such as January, September and October show small increases in non-urban
Melbourne and Victoria. In particular, in the month of March, in the non-urban
Melbourne and Victorian temperatures show decreasing trends. Year to year variations
and trends in mean temperatures (Figures 29 to 32) are stronger in central Melbourne than in
Victoria. Baseline values for Melbourne for 2006 were derived from the linear trends, as shown
in these figures.
Using a similar method, baseline values for 2006 were obtained using linear trends for monthly
HDD and EDD. In case of EDD, factors other than average temperature significantly influence
the total EDD units in winter. However, in the month of October, there is no significant
difference between HDD and EDD values. In the summer half of the year, the HDD tends to be
slightly higher than the EDD
0.04
o
Trend per year ( C)
0.03
Melbourne city
Melbourne gridbox
Victoria
0.02
0.01
0.00
-0.01
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Months
Figure 28: Annual trends in monthly mean temperature at central Melbourne,
Melbourne grid box (non-urban) and Victoria based on the period from 1950 to 2005.
Units are in °C per year.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
16
35
14
o
May 14.05 C
o
13
15
June 11.66 C
12
14
11
13
10
12
9
11
1950
1960
13
1970
1980
1990
2000
8
1950
1970
1980
1990
2000
1980
1990
2000
1980
1990
2000
13
o
July 10.97 C
Temperature (oC)
1960
August 12.01 oC
12
12
11
11
10
10
9
8
1950
1960
1970
1980
1990
2000
1960
1970
18
16
15
9
1950
o
September 13.62 oC
October 15.54 C
17
14
16
13
15
12
14
11
10
1950
1960
1970
1980
1990
2000
13
1950
1960
1970
Actual temperature
Linear trend
Figure 29: Year-to-year variations in monthly average temperatures and their trends at
central Melbourne for the winter-half of the year from 1950 to 2005. Baseline values for
the year 2006 are also shown on the top left hand corner of each plot.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
36
14
12
May 11.60 oC
13
11
12
10
11
9
10
8
9
1950
11
1960
1970
1980
1990
2000
7
1950
1960
1970
1980
1990
2000
1980
1990
2000
1980
1990
2000
11
July 8.27 oC
August 9.25 oC
10
10
o
Temperature ( C)
June 9.13 oC
9
9
8
8
7
6
1950
1960
1970
1980
1990
2000
13
7
1950
1960
1970
16
o
September 11.13 oC
October 13.48 C
12
15
11
14
10
13
9
12
8
1950
1960
1970
1980
1990
2000
11
1950
1960
1970
Actual temperature
Linear trend
Figure 30: Year-to-year variations in monthly average temperatures and their trends in
Victoria for the winter-half of the year from 1950 to 2005. Baseline values for the year
2006 are also shown on the top left hand corner of each plot.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
20
22
November 17.77 oC
21
19
19
17
18
16
17
15
16
14
1950
o
Temperature ( C)
23
1960
1970
1980
1990
2000
15
1950
24
23
21
22
20
21
19
20
18
19
17
1950
1960
1970
1960
1970
1980
1990
2000
1980
1990
2000
1980
1990
2000
25
January 20.85 oC
22
1980
1990
2000
22
21
December 19.50 oC
20
18
24
37
18
1950
February 21.54 oC
1960
1970
20
March 19.38 oC
19
April 16.65 oC
18
20
17
19
16
18
15
17
16
1950
14
1960
1970
1980
1990
2000
13
1950
1960
1970
Actual temperature
Linear trend
Figure 31: Year-to-year variations in monthly average temperatures and their trends at
central Melbourne for the summer-half of the year from 1950 to 2005. Baseline values
for the year 2006 are also shown on the top left hand corner of each plot.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
38
19
21
November 16.46 oC
18
20
17
19
16
18
15
17
14
16
13
1950
24
o
Temperature ( C)
23
1960
1970
1980
1990
2000
15
1950
23
22
22
21
21
20
20
19
19
18
18
1960
1970
1980
1990
2000
18
17
1960
1970
1980
1990
2000
1980
1990
2000
1980
1990
2000
24
January 20.24 oC
17
1950
December 18.85 oC
17
1950
February 20.93 oC
1960
1970
17
March 14.85 oC
16
16
15
15
14
14
13
13
12
12
1950
1960
1970
1980
1990
2000
11
1950
April 14.63 oC
1960
1970
Actual temperature
Linear trend
Figure 32: Year-to-year variations in monthly average temperatures and their trends in
Victoria for the summer-half of the year from 1950 to 2005. Baseline values for the year
2006 are also shown on the top left hand corner of each plot.
Year-to-year variabilities and trends in heating degree days from 1970 to 2005 (Figures
33 and 34). were analyzed using data from VENCorp. A strong decreasing trend in
heating degree days has been observed from 1970 to 2005 for the winter months and
November, but the months from December to April do not show strong decreasing
trends. The stronger decrease in winter months and November is associated with large
increases in temperature at central Melbourne in Figures 28 and 30.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
200
39
280
May 138.34
260
180
June 187.18
240
160
220
140
200
180
120
160
100
1970
1975
1980
1985
1990
1995
2000
2005
300
140
1970
o
HDD units in ( C)
1980
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
280
July 220.85
August 197.42
280
260
260
240
240
220
220
200
200
180
180
1970
1975
1980
1985
1990
1995
2000
2005
220
200
1975
160
1970
1975
1980
160
October 100.83
September 143.53
140
180
120
160
100
140
80
120
60
100
1970
1975
1980
1985
1990
1995
2000
2005
1970
1975
1980
Actual Heating Degree Days
Linear trend
Figure 33: Year-to-year variations in monthly heating degree days and their trends at
central Melbourne during the winter-half of the year from 1970 to 2005. Baseline values
for the year 2006 are also shown on the top left hand corner of each plot.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
40
120
80
November 54.01
December 29.71
100
60
80
60
40
40
20
20
0
1970
1975
1980
1985
1990
1995
2000
2005
60
0
1970
o
1980
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
40
January 10.90
HDD units in ( C)
1975
February 9.75
40
20
20
0
1970
1975
1980
1985
1990
1995
2000
2005
0
1970
1975
1980
140
80
April 72.80
March 25.36
120
60
100
40
80
20
0
1970
60
1975
1980
1985
1990
1995
2000
2005
40
1970
1975
1980
Actual Heating Degree Days
Linear trend
Figure 34: Year-to-year variations in monthly heating degree days and their trends at
central Melbourne during the summer-half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot.
Interannual variations and trends in effective degree days shown in Figures 35 and 36
strongly agree with variations and trends in monthly heating degree days. The trends in
effective degree days also show an inverse relationship with average temperature trends
at central Melbourne. Trends and variations in EDDs are very similar to trends and
variations in HDDs, because temperature is main driving factor to determine the trends
and variations. However, EDD units are higher due to the influence of factors other
than temperature, such as sunshine hours, winds and the seasonal factor. On the other
hand, heating degree days are higher in the summer-half of the year.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
240
340
May 164.48
320
220
280
180
260
160
240
140
220
120
1970
1975
1980
1985
1990
1995
2000
2005
400
EDD units
200
1970
1975
1980
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
340
July 300.14
320
360
300
340
280
320
260
300
240
280
220
260
1970
1975
1980
1985
1990
1995
2000
2005
200
1970
August 262.88
1975
1980
180
300
280
June 252.19
300
200
380
41
September 176.23
160
260
240
140
220
120
200
100
180
80
160
140
120
1970
October 97.95
60
1975
1980
1985
1990
1995
2000
2005
1970
1975
1980
Actual Effective Degree Days
Linear trend
Figure 35: Year-to-year variations in monthly effective degree days and their trends at
central Melbourne during the winter -half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
42
80
40
November 31.33
December 10.77
60
30
40
20
20
10
0
1970
1975
1980
1985
1990
1995
2000
2005
0
1970
1975
1980
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
1985
1990
1995
2000
2005
12
January 1.10
February 2.50
EDD units
8
8
4
4
0
1970
1975
1980
1985
1990
1995
2000
2005
0
1970
1975
1980
140
60
March 10.07
120
April 60.29
100
40
80
60
20
40
20
0
1970
1975
1980
1985
1990
1995
2000
2005
0
1970
1975
1980
Actual Effective Degree Days
Linear trend
Figure 36: Year-to-year variations in monthly effective degree days and their trends at
central Melbourne during the summer -half of the year from 1970 to 2005. Baseline
values for the year 2006 are also shown on the top left hand corner of each plot.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
6.3
43
Projected monthly temperature, heating degree days and
effective degree days
The construction of projected monthly average temperature follows the procedure of
Suppiah et al. (2001). However, there are some differences in considered parameters
between the previous study and the present study. In the present study, average
temperature values were estimated for each month to calculate heating degree and
effective degree days for winter and summer halves of the year. Some differences,
which are not significant, are found in the baseline temperature values that are used to
project future temperatures from 2006 and 2012. This may arise from the difference in
the length of records between the previous study and the present study. In the previous
study, we used daily average temperature data from 1965 to 2000 to project HDDs from
2003-2007, while in this study we used daily average temperature data from 1970 to
2005 to project HDD312 and EDD312 from 2007 to 2012.
Monthly average temperatures from 2007 to 2012 were projected using UHI, low,
average and high greenhouse warming values shown Figure 27, and baseline
temperatures for 2006 shown in Figure 29 and Figure 31. Projected temperatures from
2007 to 2012 for winter and summer halves of the year are shown in Figures 37 and 38.
Firstly, to calculate monthly and seasonal heating degree days, a daily average
temperature climatology was prepared using the data from 1970 to 2005. This period
was chosen because average daily temperature, heating degree days and effective
degree days are available for these years from VENCorp. Secondly, daily values of
UHI, and annual values of low, average and high greenhouse warming values for the
years from 2006 to 2012 were added to the observed daily climatology. Thirdly, daily
heating degree days were calculated using the formula explained earlier (see section 5
on page 19) and monthly and seasonal values were obtained and added to the baseline
values obtained from VENCorp data. Figure 39 shows monthly heating degree days
from May to October and Figure 40 shows the aggregated values for the winter and
summer halves of the year. Generally there is a tendency for decrease in heating degree
days as the average temperature is projected to increases due to urbanization and
greenhouse warming.
We have used the relationship between mean daily heating degree days and daily
effective degree days in Figure 22a to estimate future effective degree days. As
explained in Chapter 5, heating degree days and effective degree days are strongly
correlated with daily temperature. Estimated monthly effective degree days for May to
October are shown in Figure 41 and EDDs for winter and summer halves of the year are
shown in Figure 42.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
44
14.4
11.9
May
June
14.3
11.8
14.2
11.7
14.1
14.0
2006
2007
2008
2009
2010
2011
2012
11.6
2006
July
o
2008
2009
2010
2011
2012
2008
2009
2010
2011
2012
2008
2009
2010
2011
2012
12.3
11.2
Temperature ( C)
2007
August
12.2
11.1
12.1
11.0
12.0
10.9
2006
2007
2008
2009
2010
2011
2012
14.0
11.9
2006
2007
15.9
October
September
13.9
15.8
13.8
15.7
13.7
15.6
13.6
2006
2007
2008
2009
2010
2011
2012
15.5
2006
2007
Baseline+uhi
Baseline+uhi+lgw
Baseline+uhi+agw
Baseline+uhi+hgw
Figure 37: Projected monthly average temperature for the winter-half of the year using
the values from Figures 27 and 29. Baseline refers to the value for the year 2006. Uhi,
lgw, agw and hgw refer to urban heat island index, and low, average and high
greenhouse warming, respectively.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
November
45
December
19.7
17.9
19.6
17.8
19.5
17.7
2006
2007
2008
2009
2010
2011
2012
19.4
2006
o
Temperature ( C)
January
21.7
20.9
21.6
2007
2008
2009
2010
2011
2012
2008
2009
2010
2011
2012
2008
2009
2010
2011
2012
February
21.0
20.8
2006
2007
2008
2009
2010
2011
2012
21.5
2006
2007
19.7
April
March
19.6
16.9
19.5
16.8
19.4
16.7
19.3
2006
2007
2008
2009
2010
2011
2012
16.6
2006
2007
Baseline+uhi
Baseline+uhi+lgw
Baseline+uhi+agw
Baseline+uhi+hgw
Figure 38: Projected monthly average temperature for the summer-half of the year
using the values from Figures 27 and 31. Baseline refers to the value for the year
2006. Uhi, lgw, agw and hgw refer to urban heat island index, and low, average and
high greenhouse warming, respectively.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
46
190
140
139
May 138.3377
188
138
137
186
136
184
135
134
182
133
132
180
131
130
2006
2007
2008
2009
2010
2011
2012
o
HDD units in ( C)
178
2006
July 220.85
199
2008
2009
2010
2011
2012
2009
2010
2011
2012
2009
2010
2011
2012
August 197.42
198
220
197
218
196
216
194
214
193
195
192
212
191
210
2006
2007
2008
2009
2010
2011
2012
146
145
2007
200
224
222
June 187.1816
190
2006
2007
2008
104
September 143.53
102
144
143
100
142
98
141
140
96
139
94
138
92
137
136
2006
October 100.82
2007
2008
2009
2010
2011
2012
90
2006
2007
2008
Clim+uhi
Clim+uhi+lgw
Clim+uhi+agw
Clim+uhi_hgw
Figure 39: Projected monthly average heating degree days for the winter -half of the
year using the contributions from urbanization and greenhouse warming. Baseline
values for the year 2006 are shown at the top left hand corner of each plot. Clim, uhi,
agw and hgw refer to daily climatology from 1970-2005, and low, average and high
greenhouse warming, respectively.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
47
1000
995
May to October 988.14
990
HDD units (oC)
985
980
975
970
965
960
955
950
2006
2007
2008
2009
2010
2011
2012
2010
2011
2012
Year
190
November to April 180.23
HDD units (oC)
185
180
175
170
165
160
2006
2007
2008
2009
Year
Clim+uhi
Clim+uhi+lgw
Clim+uhi+agw
Clim+uhi+hgw
Figure 40: Projected average heating degree days for winter and summer halves of
the year from 2006 to 2012. The baseline values for 2006 are also shown on the top
left hand corner of each figure. Clim, uhi, agw and hgw refer to daily climatology from
1970-2005, and low, average and high greenhouse warming, respectively.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
48
248
160
158
May 156.65
246
244
156
242
154
240
152
238
150
236
148
234
232
146
2006
300
EDD units
298
June 244.10
2007
2008
2009
2010
2011
2012
230
2006
2008
2009
2010
2011
2012
2009
2010
2011
2012
2009
2010
2011
2012
262
July 296.12
260
296
258
294
256
292
254
August 258.40
252
290
250
288
248
286
284
2006
2007
246
2007
2008
172
170 September 167.34
168
166
164
162
160
158
156
154
152
150
2006
2007
2008
2009
2010
2011
2012
2006
2007
2008
100
98
October 94.12
96
94
92
90
88
86
84
82
2009
2010
2011
2012
80
2006
2007
2008
Clim+uhi
Clim+uhi+lgw
Clim+uhi+agw
Clim+uhi_hgw
Figure 41: Projected monthly average effective degree days for the winter half of the
year for central Melbourne from 2006 to 2012. The baseline values for 2006 are also
shown on the top left hand corner of each plot. Clim, uhi, agw and hgw refer to daily
climatology from 1970-2005, and low, average and high greenhouse warming,
respectively.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
49
1250
1240
May to October 1216.73
1230
1220
EDD units
1210
1200
1190
1180
1170
1160
1150
1140
2006
2007
2008
2009
2010
2011
2012
2010
2011
2012
Year
110
November to April 107.65 (2005)
105
EDD units
100
95
90
85
80
2006
2007
2008
2009
Year
Clim+uhi
Clim+uhi+lgw
Clim+uhi+agw
Clim+uhi+hgw
Figure 42: Projected average effective degree days for the winter and summer halves
of the year for central Melbourne from 2006 to 2012. The baseline values for 2006 are
also shown on the top left hand corner of each figure. The base line for the winter half
year is from May to October, 2006 and the baseline value for the summer-half is from
November 2005 to April 2006. Clim, uhi, agw and hgw refer to daily climatology from
1970-2005, and low, average and high greenhouse warming, respectively.
50
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Tables 1 through 3 show projected average temperature, heating degree days and
effective degree days for winter and summer halves of the year and annual from 2006 to
2012. The winter half year is from May to October, and the summer half is from
November of the previous year to April of the current year. The annual values are from
January to December of the current year. The annual increases in average temperature
and annual decreases in HDD312 and EDD312 are given so that the changes in EDD312
projected by VENCorp (2006) can be compared with the results of the present study.
The annual UHI contribution increases by 0.0133°C/per year, annual UHI+low
greenhouse warming contribution increases by 0.018°C/per year, annual UHI +average
greenhouse warming increases by 0.032°C and UHI + high greenhouse warming
contribution increases by 0.0.38°C. Such increases in average temperature result in
annual decreases of 0.43, 1.93, 5.78, and 8.1 HDDs312. The increases in average
temperature lead to annual decreases of 0.48, 2.43, 7.28 and 10.23 EDDs312 by 2012.
A comparison with projected EDDs312 by VENCorp (2006) and the present study shows
a good agreement on decreases in EDDs312. VENCorp (2006) suggested an annual
decrease of 7.0 to 7.6 EDD312 for the period from 2007 to 2011, which is very close to
the annual decrease of EDD312 for the combined effects of urbanization and average
greenhouse warming (7.28 EDD312) in the present study. The annual decrease in
EDDs312 estimated by VENCorp (2006) is based on a simple extrapolation of the
current trend in average temperature in Melbourne weather station. Although the
decrease in annual EDDs312 estimated by VENCorp (2006) is very close to the annual
decrease estimated from this study for UHI+average greenhouse warming, the decline
in UHI+average greenhouse warming is based on a robust statistical analysis
considering, trends in urbanization related to future population changes, greenhouse
warming and any contribution to natural temperature trends in Melbourne. Furthermore,
the present study, provides ranges in projected temperature, HDD312 and EDD312 based
UHI and three greenhouse warming scenarios.
The estimated annual EDD312 for the year 2007 in this study is slightly lower
(EDD312=1314) than the values by VENCorp (2006), which is 1355 EDD312. The
discrepancy could arise from different methodologies and number of years used in these
studies.
Considering the narrow range in the warming shown in Figure 25 and the period used to
project temperature, HDD312 and EDD312 in this study (2007-2012), it is reasonable to
choose the projected temperature, HDD312 and EDD312 for the UHI+average
greenhouse warming case for any short-term sensitivity analysis or application.
However, it is worth considering the UHI+low greenhouse warming and UHI+high
greenhouse warming cases for long-term planning.
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
51
Table 1: Projected average temperature (oC) for Melbourne central for winter, summer
halves and annual from 2007 to 2012. Baseline values of monthly temperatures in
2006 were added to four cases; urban heat island (UHI) growth, UHI plus low
greenhouse warming (lgw), UHI plus average greenhouse warming (agw) and UHI plus
high greenhouse warming (hgw).
Winter half
Year
2006
2007
2008
2009
2010
2011
2012
UHI
12.98
12.99
13.00
13.02
13.03
13.04
13.06
UHI+lgw
12.98
12.99
13.01
13.03
13.05
13.07
13.09
UHI+agw
12.98
13.00
13.04
13.07
13.10
13.13
13.16
UHI+hgw
12.98
13.01
13.05
13.09
13.13
13.17
13.21
Summer half
Year
2006
2007
2008
2009
2010
2011
2012
UHI
19.28
19.29
19.31
19.32
19.33
19.35
19.36
UHI+lgw
19.28
19.30
19.32
19.34
19.35
19.37
19.39
UHI+agw
19.28
19.31
19.34
19.37
19.40
19.44
19.47
UHI+hgw
19.28
19.32
19.36
19.39
19.43
19.47
19.52
Annual
Year
2006
2007
2008
2009
2010
2011
2012
UHI
16.13
16.14
16.16
16.17
16.18
16.20
16.21
UHI+lgw
16.13
16.15
16.16
16.18
16.20
16.22
16.24
UHI+agw
16.13
16.16
16.19
16.22
16.25
16.28
16.32
UHI+hgw
16.13
16.16
16.20
16.24
16.28
16.32
16.36
52
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Table 2: Projected average heating degree days (HDDs312) for Melbourne central for
winter, summer halves and annual from 2007 to 2012. Baseline values of monthly
HDDs in 2006 were added to three cases; UHI, low, average and high greenhouse
warming. Baseline values of HDDs monthly in 2006 were added to four cases; urban
heat island (UHI) growth, UHI plus low greenhouse warming (lgw), UHI plus average
greenhouse warming (agw) and UHI plus high greenhouse warming (hgw).
Winter half
Year
2006
2007
2008
2009
2010
2011
2012
UHI
988.1
988.1
988.0
987.9
987.8
987.7
987.6
UHI+lgw
988.1
987.2
986.2
985.1
984.1
983.0
981.9
UHI+agw
988.1
984.9
981.5
978.1
974.5
970.8
967.0
UHI+hgw
988.1
983.6
978.9
973.9
968.8
963.5
957.9
Summer half
Year
2006
2007
2008
2009
2010
2011
2012
UHI
180.2
179.9
179.5
179.2
178.9
178.5
178.2
UHI+lgw
180.2
179.4
178.5
177.6
176.7
175.8
174.9
UHI+agw
180.2
178.1
175.9
173.7
171.4
169.0
166.7
UHI+hgw
180.2
177.4
174.5
171.5
168.4
165.2
161.8
Annual
Year
2006
2007
2008
2009
2010
2011
2012
UHI
1168.4
1167.9
1167.5
1167.1
1166.7
1166.2
1165.8
UHI+lgw
1168.4
1166.5
1164.6
1162.7
1160.8
1158.8
1156.8
UHI+agw
1168.4
1163.1
1157.5
1151.9
1146.0
1139.8
1133.7
UHI+hgw
1168.4
1161.0
1153.3
1145.4
1137.2
1128.6
1119.8
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
53
Table 3: Projected average effective degree days (EDDs312) for Melbourne central for
winter, summer halves and annual from 2007 to 2012. Daily EDD312 values were
estimated using the relationship shown in Figure 22a to get monthly values. . Baseline
values of EDDs monthly in 2006 were added to four cases; urban heat island (UHI)
growth, UHI plus low greenhouse warming (lgw), UHI plus average greenhouse
warming (agw) and UHI plus high greenhouse warming (hgw).
Winter Half
Year
2006
2007
2008
2009
2010
2011
2012
UHI
1216.7
1216.6
1216.5
1216.3
1216.2
1216.0
1215.9
UHI+lgw
1216.7
1215.1
1213.5
1211.8
1210.1
1208.4
1206.6
UHI+agw
1216.7
1211.6
1206.2
1200.9
1195.2
1189.2
1183.2
UHI+hgw
1216.7
1209.5
1202.0
1194.2
1186.1
1177.6
1168.8
Summer half
Year
2006
2007
2008
2009
2010
2011
2012
UHI
104.7
104.3
104.1
103.7
103.4
103.0
102.7
UHI+lgw
104.7
103.9
103.2
102.5
101.7
100.9
100.2
UHI+agw
104.7
103.1
101.4
99.7
98.0
96.2
94.5
UHI+hgw
104.7
102.6
100.4
98.2
95.9
93.6
91.2
Annual
Year
2006
2007
2008
2009
2010
2011
2012
UHI
1321.4
1320.9
1320.5
1320.0
1319.5
1319.0
1318.5
UHI+lgw
1321.4
1319.1
1316.7
1314.3
1311.8
1309.3
1306.8
UHI+agw
1321.4
1314.7
1307.6
1300.6
1293.1
1285.4
1277.7
UHI+hgw
1321.4
1312.1
1302.4
1292.4
1282.0
1271.2
1260.0
54
6.4
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
Uncertainties associated with future temperature, HDD
and EDD
In the present study, uncertainties associated with baseline monthly average
temperature for the year 2006 and the range of greenhouse warming from 2006 to 2012
have been quantified. Future greenhouse warming is associated with uncertainties in
future human behaviour, economic and technological change and differences in regional
patterns of climate change simulated by climate models. Although the simulations have
significantly improved in recent years with new physical parameterisations and finer
horizontal, still these models do not accurately simulate the climate over regions as
small as Melbourne. Since the heating degree days and effective degree days are
strongly correlated with average daily temperature, any uncertainties associated with
temperature can influence the projected values of heating and effective degree days.
There are a number of uncertainties associated with the future trend in urbanisation in
Melbourne after 2005. These include uncertainties associated with future population
growth (natural and migration), technological changes associated with building
characteristics, urban development, economic growth and development, supply and
demand for energy. Changes and trends in these factors are not well understood.
The projected changes in average temperature, heating degree days and effective degree
days are based on the linear trend in urbanisation and climate model projections.. These
projected values do not include the influences of natural variability on the year-to-year
time scale. Factors associated with natural variability, such as ENSO, the Antarctic
Circumpolar wave, Southern Annular Mode and volcanic eruption are not easily
predictable in this time scale, 2006-2012.
6.5
A comparison between the previous CSIRO study and
the present study
There are a number of similarities and differences between the previous CSIRO study
(Suppiah et al., 2001) and the present study. These include methodology, considered
parameters and results.
In the previous and the present studies, the same methodology is used to calculate the
urban heat island index and greenhouse warming. Temperature data from the grid box
representing Melbourne are used as a proxy for non-urban Melbourne temperatures.
Melbourne’s weather station data represent central Melbourne. Although CSIRO
projections were made relative to 1990, the warming in Melbourne was calculated
relative to 2000 in the previous study and 2006 in the present study.
In the previous study, we estimated annual temperature and HDD values from 2003 to
2007, but in the present study we provide estimates of monthly as well as seasonal
temperatures, HHDs312 and EDDs312 from 2006 to 2012. In particular, EDDs312 have
been estimated using the empirical relationship between observed daily mean HHDs312
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
55
and EDDs312. In the previous study, the baseline annual temperature for 2000 was
15.88°C with an uncertainty range of 16.09°C to 15.68°C. In the present study, the
baseline annual temperature for 2006 is 16.13°C which is slightly higher due to warmer
conditions in recent years. Since the previous study focused on annual temperature and
annual HDD values, only projected annual temperature and HHD values for 2007 can
be easily compared with the present results. The projected annual average temperature
for 2007, based greenhouse warming plus urbanization in the previous study, it was
16.00°C with a range between 15.71°C and 16.29°C. In the present study, the projected
annual average temperature is 16.16°C which ranges from 16.15 and 16.16 for the year
2007. The upper range is very close to the mid range, if we consider two decimal points.
It is worth mentioning that there is a significant difference in the range of projected
temperatures between the present and the previous study. The wider range in the
previous study was a result of the statistical method, which determined the upper and
lower range temperature values based on 90% confidence limits. However, in the
present study, projected temperatures are calculated by adding the UHI and greenhouse
warming contributions to the baseline temperature of the year 2006, which was derived
from the linear trend from 1950 to 2005.
In the previous study (Suppiah et al., 2001), the contribution of projected greenhouse
and urbanization gave a range of 1111 to 1154 with the midpoint of 1132 annual HDD
by 2007. In the current study, the projected annual HDD312 range between 1161 and
1168. This difference can also arise from different years of consideration and methods.
56
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
7.
CONCLUSIONS
The results presented in this report are based on a project undertaken by CSIRO for SP
AusNet on behalf of three gas distribution businesses (Multinet, Envestra and Sp
AusNet). We have assessed growth in the urban heat island effect on both observed and
projected Melbourne temperature, heating degree days and effective degree days in
Melbourne and Victoria over the period 2008-2012.
Temperatures in Victoria indicate a greater rate of warming after 1950 than before.
From 1950 to 2005, the maximum temperature increased by 0.71ºC (0.13ºC per
decade), the minimum temperature increased by 0.44ºC (0.08ºC per decade) and the
average temperatures rose by 0.58ºC (0.10ºC per decade). These are slightly higher than
the value shown in Suppiah et al. (2001) for the period from 1950 to 2000.
From 1950 to 2005, Melbourne’s maximum temperature increased by 0.81°C (0.14°C
per decade), the minimum temperature increased by 1.79°C (0.32°C per decade) and the
mean temperature increased by 1.30°C (0.23°C per decade). Contributions to this
warming include urbanization, greenhouse warming and natural variability.
The annual warming at central Melbourne from 1950 to 2005 due to the combined
effects of urbanization, natural variability and greenhouse effect is estimated to be
+0.023°C per year, of which 0.012°C per year is from urbanization. The effect of
urbanization shows an annual cycle with weak contribution during June and strong
contributions in April and September. The estimated contributions of the combined
effect of urbanization and greenhouse warming range from 0.02 to 0.04°C in 2007 with
an average warming of 0.03°C, 0.05 to 0.12°C in 2009 with an average warming of
0.09°C and 0.12°C to 0.24°C in 2012 with an average warming of 0.18°C.
Monthly baseline temperatures for 2006 for central Melbourne were estimated using
linear trends from 1950 to 2005. The baseline temperatures for 2006 for winter and
summer halves, and for annual are 12.98°C, 19.28°C and 16.13°C, respectively. The
annual increases of UHI, UHI+low greenhouse warming, UHI+average greenhouse
warming and UHI+high greenhouse warming for the years from 2007 to 2012 are
0.012°C, 0.018°C, 0.032°C and 0.038°C per year, respectively.
Monthly, seasonal and annual HDDs312 were estimated using a daily temperature
climatology from 1970 and 2005, and contributions of UHI and greenhouse warming
from 2007 to 2012. The baseline HDDs312 for 2006 for winter and summer halves of
the year, and for annual are 988.1, 180.2 and 1168.1, respectively. The annual decreases
in HDD312 for UHI, UHI+low greenhouse warming, UHI+average greenhouse warming
and UHI+high greenhouse warming for the years from 2007 to 2012 are 0.43, 1.93,
5.78, and 8.1 HDDs312 per year.
On the basis of the empirical relationship between daily average HDDs312 and EDDs312
from 1970 to 2005, monthly, seasonal and annual EDDs312 are projected for the period
from 2007 to 2012. The baseline EDDs312 for 2006 for winter and summer halves of the
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
57
year, and annual are 1216.7, 104.7 and 1321.4, respectively. The annual decreases in
EDD312 for UHI, UHI+low greenhouse warming, UHI+average greenhouse warming
and UHI+high greenhouse warming for 2007 to 2012 are 0.48, 2.43, 7.28 and 10.2,
respectively.
A comparison between projected EDDs312 for the UHI+average greenhouse warming in
the present study and by VENCorp (2006) shows a decrease of 7 EDDs312 per year.
However, the annual decreases in EDDs312 in the present study range from 2.43 to 10.2
between UHI+low greenhouse warming and UHI+high greenhouse warming from 2007
and 2012.
Considering the narrow range in the warming and the period used in this study (20072012), it is reasonable to choose the projected temperature, HDD312 and EDD312 for the
UHI+average greenhouse warming case for any short-term sensitivity analysis or
application. However, it is worth considering the UHI+low greenhouse warming and
UHI+high greenhouse warming cases for long-term planning.
58
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
8.
REFERENCES
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exchanges of energy and water, and the urban heat island. International Journal
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Australian Bureau of Statistics, 2000. Year Book Australia 2000. Australian Bureau of
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CSIRO, 2001. Climate Change Projections for Australia. CSIRO, Atmospheric
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Della-Marta, P.M., Collins, D. and Braganza, K. 2004. Updating Australia’s high
quality annual temperature dataset. Australian Meteorological Magazine, 53,
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IPCC, 2001. Climate Change 2001. The Scientific Basis of Climate Change. Summary
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Jones, D. A. and Trewin, B. C. 2000. On the relationships between the El NiñoSouthern oscillation and Australian land surface temperature. International
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Jones, P. D. and Moberg, A. 2003. Hemispheric and large-scale surface air temperature
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Karoly, D.J. and Braganza. K. 2005. Attribution of recent temperature changes in the
Australian region. Journal of Climate, 18, 457-464.
Morris, C. J. G., Simmons, I. and Plummer, N. 2001. Quantification of the influences
of wind and cloud on the nocturnal urban heat island of a large city. Journal of
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Nicholls, N. and Collins, D. 2006. Observed change in Australia over the past century.
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Oke, T. R. 1987. Boundary layer climates. Second Edition, Methuen., New York,
435p.
Parker, D. E. 2004. Large-Scale Warming is not urban. Nature, 432, 290
Simmonds, I. and Keay, K. 1997. Weekly cycle of meteorological variations in
Melbourne and the role of pollution and anthropogenic heat release.
Atmospheric Environment, 31, 1589-1603.
Suppiah, R., Whetton, P. H. and Hennessy, K. J. 2001. Projected changes in
temperature and heating degree-days for Melbourne, 2003-2007. CSIRO
Atmospheric Research, 19p.
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Torok, S. J., Morris, C. J. G., Skinner, C. and Plummer, N. 2001. Urban heat island
features of southeast Australian towns. Australian Meteorological Magazine, 50,
1-13.
VENCorp, 2003. Review of EDD weather standards. Response to submissions,
summary and final recommendations. Victorian Energy Networks Corporation,
9pp
VENCorp, 2006. Review of the effective degree day weather standards. Final Report,
Victorian Energy Networks Corporation, 36pp.
Whetton, P. H., McInnes, K. L., Jones, R. N., Hennessy, K. J., Suppiah, R., Page, C. M.,
Bathols, J. and Durack, P. J. 2005. Australian climate change projections for
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Atmospheric Research Paper 001, Aspendale, 34pp.
60
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
APPENDIX
CDT312=Cold Day Temperature
DT312= Daily temperature
HDD312= Heating Degree Day
EDD312= Effective Degree Day
Figure 19:
CDT312= -3.6656 + 1.72795*DT312 + -0.03586*DT3122
Figure 20a:
HDD312= 14.284453 - 0.041706* DT312 -0.087765* DT3122 + 0.002765* DT3123.
Figure 20b
HDD312= 17.73181 – 0.98486 *CDT312
Figure 21a
EDD312= 41.086307 – 3.949018 * DT312 + 0.094618 *DT3122
Figure 21b
EDD312= -74.618835 +22.824262 * DT312 -1.925616 *DT3122 + 0.049495 * DT3123
Figure 22a
EDD312= - 0.059569 + 0.092663 * HDD312 + 0.337413 *HDD3122 - 0.022402* HDD3123
Figure 22b
EDD312= 1.310590 – 0.639369 * HDD312 + 0.446535 *HDD3122 - 0.027172* HDD3123
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
61
GLOSSARY OF TERMS
Anthropogenic: Of human origin; man made
Climate model: Complex computer models that represent the atmosphere-ocean climate system
based on mathematical equation governing the behaviour of the various components of
the system and including treatments of physical processes and interactions.
Climate scenario: A plausible and often simplified representation of the future climate, based
on an internally consistent set of climatological relationships, that has been constructed
for explicit use in investigating the potential consequences of anthropogenic climate
change, often serving as input to impact models. Climate projections often serve as the
raw material for constructing climate scenarios, but climate scenarios usually require
additional information such as the observed current climate. A climate change scenario
is the difference between a climate scenario and the current climate.
Climate sensitivity: The magnitude of a climatic response to a perturbing influence. In
mathematical modelling of the climate system, it is the difference between simulations
as a function of a change in a given parameter. In IPCC reports, equilibrium climate
sensitivity refers to the equilibrium change in global mean surface temperature
following a doubling of the atmospheric (equivalent) CO2 concentration. In general,
equilibrium climate sensitivity refers to the equilibrium change in surface temperature
following a unit change in radiative forcing (°C/W m-2).
Climate system: The climate system is the highly complex system consisting of five major
components: the atmosphere, the hydrosphere, the cryosphere, the land surface and the
biosphere, and the interactions between them. The climate system evolves in time under
the influence of its own internal dynamics and because of external forcings such as
volcanic eruptions, solar variations, and human-induced forcings such as the changing
composition of the atmosphere and land-use change.
Climate variability: Climate variability refers to variations in the mean state and other statistics
(such as standard deviations, the occurrence of extremes, etc.) of the climate on all
temporal and spatial scales beyond that of individual weather events. Variability may
be due to natural internal processes within the climate system (internal variability), or to
variations in natural or anthropogenic external forcing (external variability).
Drought: The phenomenon that exists when precipitation has been significantly below normal
record levels, causing serious hydrological imbalances that adversely affect land
resource production systems.
Emission scenario: A plausible representation of the future development of emissions of
substances that are potentially radiatively active (e.g., greenhouse gases, aerosols),
based on a coherent and internally consistent set of assumptions about driving forces
(such as demographic and socio-economic development, technological change) and
their key relationships. Concentration scenarios, derived from emissions scenarios, are
used as input into a climate model to compute climate projections.
Global surface temperature: The global surface temperature is the area-weighted global
average of (i) the sea surface temperature over the oceans (i.e., the sub-surface bulk
62
Projected changes in temperature and heating degree-days for Melbourne and Victoria, 2008-2012
temperature in the first few meters of the ocean), and (ii) the surface air temperature
over land at 1.5 m above the ground.
Greenhouse effect: Greenhouse gases effectively absorb infrared radiation, emitted by the
earth’s surface, by the atmosphere itself due to the same gases, and by clouds.
Atmospheric radiation is emitted to all sides, including downward to the earth’s surface.
Thus greenhouse gases trap heat within the surface-troposphere system. This is called
the “natural greenhouse effect”. Atmospheric radiation is strongly coupled to the
temperature of the level at which it is emitted. In the troposphere, the temperature
generally decreases with height. Effectively, infrared radiation emitted to space
originates from an altitude with a temperature of, on average, -19°C, in balance with the
net incoming solar radiation, whereas the earth’s surface is kept at a much higher
temperature of, on average, +14°C. An increase in the concentration of greenhouse
gases leads to an increased infrared opacity of the atmosphere, and therefore, to an
effective into space from a higher altitude at a lower temperature. This causes a
radiative forcing, an imbalance that can only be compensated for by an increase of the
temperature of the surface-troposphere system. This is the “enhanced greenhouse
effect”.
Greenhouse gases: Those gases, such as water vapour, carbon dioxide, ozone, methane, nitrous
oxide, and chlorofluorocarbons, that are fairly transparent to the short wavelengths of
solar radiation but efficient at absorbing the longer wavelengths of the infrared radiation
emitted by the earth and atmosphere.
SRES scenarios: The IPCC Special Report on Emission Scenarios (SRES) is based on a range
of assumptions about population, energy sources and regional or global approaches to
development and socio-economic arrangements. The scenarios do not include any
specific greenhouse gas mitigation activities. These SRES scenarios are used as a basis
for the climate projections in the IPCC Working Group I contribution to the Third
Assessment report (IPCC, 2001). Details are available in IPCC reports.
Uncertainty: An expression of the degree to which a value (e.g., the future state of the climate
system) is unknown. Uncertainty can result from lack of information or from
disagreement about what is known or even knowable. It may have many types of
sources, from quantifiable errors in the data to ambiguously defined concepts or
terminology, or uncertain projections of human behaviour. Uncertainty can therefore be
represented by quantitative measures (e.g. a range of values calculated by various
models) or by qualitative statements (e.g. reflecting the judgement of a team of experts).
Urban heat island: Closed isotherms showing an area of the surface that is relatively warm;
most commonly associated areas of human disturbance such as towns and cities.
Vulnerability: The extent to which climate change may damage or harm a system; it depends
not only a system’s sensitivity, but also on its ability to adapt to new climatic
conditions.