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Climate Change and Variability –
Tasman District
NIWA Client Report: WLG2008-51
June 2008
NIWA Project:ELF07201
Climate Change and Variability – Tasman
District
David Wratt
Brett Mullan
Douglas Ramsay
Marina Baldi
Prepared for
Tasman District Council
NIWA Client Report: WLG2008- 51
June 2008
NIWA Project: ELF07201
National Institute of Water & Atmospheric Research Ltd
301 Evans Bay Parade, Greta Point, Wellington
Private Bag 14901, Kilbirnie, Wellington, New Zealand
Phone +64-4-386 0300, Fax +64-4-386 0574
www.niwa.co.nz
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Contents
Executive Summary
iv
1.
Introduction
1
2.
Background: Global Climate Change – Science and Impacts
2
2.1
The Physical Science Basis (IPCC Working Group I):
2
2.2
Impacts, Adaptation and Vulnerability (IPCC Working Group 2):
3
2.3
Mitigation of Climate Change (IPCC Working Group 3):
4
3.
4.
Background: New Zealand Climate Change – Science and Impacts
4
3.1 Sectoral Impacts
5
Present Climate
8
4.1
Spatial Patterns in Tasman’s Climate
8
4.2
Temporal Variability in Tasman’s Climate
10
4.3
Natural factors causing fluctuation in climate patterns over New
Zealand
11
4.3.1
The effect of El Niño and La Niña
11
4.3.2
The effect of the Interdecadal Pacific Oscillation.
13
4.4
5.
New Zealand Sea Level Trends and Variability
Projections of Tasman’s Future Climate
15
16
5.1
Tasman Climate Change Temperature Projections
17
5.2
Projections for Frosts and Hot Days under Climate Change
20
5.3
Tasman Climate Change Rainfall Projections
21
5.4
Scenarios for Changes in Extreme Rainfall
23
5.5
Evaporation, Soil Moisture and Drought
26
5.6
Wind
26
5.7
Climate Change and Sea Level
27
5.7.1
Effect of Sea-Level Rise on High Tide Exceedance
Frequency
30
5.8
Climate Change Impacts on Other Coastal Hazard Drivers
31
5.9
Considering both Anthropogenic and Natural Changes
31
6.
Tasman District – Impacts, Vulnerability and Adaptation
33
7.
References
35
APPENDIX: Rainfall depth/duration/frequency statistics and scenarios
for Richmond
39
Reviewed by:
Approved for release by:
Dr Andrew Tait
Dr Andrew Laing
Executive Summary
This report describes changes which may occur over the coming century in the climate of the region
administered by the Tasman District Council, and outlines some possible impacts of these changes.
To set the context, we summarise key findings of the recent (2007) global climate change assessment
undertaken by the Intergovernmental Panel on Climate Change. Warming of the climate system is
‘unequivocal’, and most of the observed increase in globally averaged temperatures since the mid-20th
century is very likely due to the increase in greenhouse gas concentrations caused by human activities.
The IPCC updates projections for global and regional changes in temperature, sea level, and
precipitation (rain and snow fall) for the coming century, and points to an expected increase in the
frequency of heavy rainfall events. Recent global warming is already having physical and biological
effects in many parts of the world. Projected impacts on many natural and managed systems associated
with various levels of future warming are outlined. Work assessed by the IPCC indicates that limiting
future global warming to targets which are currently being discussed internationally would require
substantial reductions in global greenhouse gas emissions from human activities.
Next, information is summarised about expected New Zealand national and regional impacts of
climate change, from the IPCC chapter on Australia and New Zealand. The Australia / New Zealand
region has warmed by 0.3 – 0.7 °C since 1950, with more heat waves, fewer frosts, more rain in
southwest New Zealand, less rain in northeastern New Zealand, and a rise in sea level since 1950 of
about 70 mm. Ongoing vulnerability in New Zealand and Australia to extreme events is demonstrated
by substantial economic losses caused by droughts, floods, fire, tropical cyclones, and hail. During the
21st century, New Zealand’s climate is virtually certain to warm further, with noticeable changes in
extreme events. Heat waves and fire risk are virtually certain to increase in intensity and frequency.
Floods, landslides, droughts and storm surges are likely to become more frequent and intense, and
snow and frost to become less frequent. Large areas of eastern New Zealand are likely to have less soil
moisture, although western New Zealand is likely to receive more rain. The potential impacts of
climate change are likely to be substantial without further adaptation. New Zealand and Australian
ecosystems, water security, and coastal communities are projected to become vulnerable if global
temperature rises by 1.5°C to 2°C, even with adaptive measures. Energy security, health, agriculture,
and tourism have considerable coping ranges and adaptive capacity, but will become vulnerable if
warming exceeds 3.0° C.
Tasman District’s present climate is then described. An upward trend, consistent with the overall New
Zealand warming through the 20th century, is apparent at the long-term climate monitoring site at
Appleby. There are substantial year to year fluctuations in temperature superimposed on this long-term
trend, with some years being nearly 2°C different from others. There is also substantial year to year
variation in rainfall. For example, Appleby exhibits annual rainfall totals ranging from around 600 mm
Climate Change and Variability – Tasman District
iv
up to more than 1400 mm. Maps are provided of the average patterns of Tasman District rainfall. Two
natural fluctuations leading to year-to-year variations are the El Niño-Southern Oscillation (ENSO),
and the Interdecadal Pacific Oscillation (IPO). These factors also lead to fluctuations in sea level.
Mid-range future temperature scenarios for Tasman District are a warming of about 0.9°C by 2040,
and of about 2.0°C by 2090 (relative to the temperature average from 1980 to 1999). Results averaged
across 12 different IPCC climate models (spatially downscaled to show variations across the Tasman
district) and over a range of (IPCC) greenhouse gas emissions scenarios project a small increase in
annual average rainfall as this century progresses, for much of the area of coastal plains adjacent to
Tasman Bay (i.e. Motueka, Waimea plains). This reflects projections of slightly more rainfall in most
seasons except spring. From these 12-model averages the western part of Tasman District is projected
to experience slightly less rainfall in summer (a change of less than 5%) but significantly more rainfall
in winter, especially by 2090. However there are significant differences in the projected magnitudes of
rainfall change between the 12 individual models from which the averages were obtained. Year to year
and decade to decade natural fluctuations similar to those experienced through the 20th Century will be
superimposed on the long-term “human-induced” trends in climate described above.
Projections for Tasman for the coming century also include a substantial decrease in frost days, an
increase in the number of very hot days, and an increase in the frequency of very heavy rainfall. For
engineering purposes some scenarios for changes in rainfall depth / duration / frequency statistics are
provided for Richmond. A possible increase in drought frequency is projected for the plains adjacent
to Tasman Bay, but this requires further analysis using the latest climate change scenarios. A small
increase by 2100 in the strongest winds cannot be ruled out. New guidance on planning for sea level is
expected shortly from the Ministry for the Environment. In the interim we suggest using a minimum
sea-level rise scenario of 0.5 metres by the 2090s (2090 to 2099) relative to the 1980-1999 average for
coastal planning, plus an assessment of sensitivity to possible higher mean sea levels. For longer-term
considerations an allowance for further sea-level rise of 10 mm/year beyond 2100 is recommended.
The Council is referred to material published by the Ministry for the Environment for guidance on
assessing likely vulnerability and impacts for the Tasman Region of these projected climate changes,
and for considering adaptation options. Relevant issues could include:
•
•
•
•
•
•
•
implications for planning and development in coastal areas of sea level rise and changes to coastal
hazards
implications for water demand, availability and allocation (including planning for irrigation
schemes and storage) of potential changes in rainfall and of drought frequency
implications for roading and stormwater drainage, lifelines planning, and civil defence and
emergency management of changes in extreme rainfall, erosion risk and coastal hazards
opportunities which climate change may bring for new horticultural crops
implications for land use planning of potential changes including floods and coastal hazards
implications for aquaculture and fisheries
implications for natural ecosystems (both terrestrial and marine) and their management.
Climate Change and Variability – Tasman District
v
1.
Introduction
This report describes changes which may occur over the coming century in the climate
of the region administered by the Tasman District Council, and outlines some possible
impacts of these changes. The report does not address the issue of mitigation (reducing
greenhouse gas emissions, or increasing “sinks” such as areas of growing forest), apart
from a brief summary of recent findings of the Intergovernmental Panel on Climate
Change.
Consideration is given both to possible natural variations in the climate, and to
changes which may result from increasing global concentrations of greenhouse gases
caused by human activities. Climatic factors discussed include temperature, rainfall,
wind, evaporation, soil moisture, and sea level.
Fig 1:
The Tasman District Council Area: The region administered by the Council is
shaded in grey. (Tasman District Council, 2005)
Climate Change and Variability – Tasman District
1
Possible changes along the coast in sea level, storm surge and wave climate are also
considered, as are changes in river flows (both low flows and floods). Figure 1 shows
the Tasman District Council region.
Preparation of the report has been supported through a small Envirolink contract. This
did not fund any new data analysis, but enabled us to draw on information which is
already available from various sources. Much of this information is very new,
resulting from the latest assessments of the Intergovernmental Panel on Climate
Change (IPCC 2007a, 2007b, 2007c), and scenarios for New Zealand obtained by
NIWA scientists based on downscaling from global climate model runs undertaken for
these IPCC assessments. This updated regional information has been published by the
Ministry for the Environment in a revised guidance manual for New Zealand Local
Government organizations on climate change effects and impacts assessment
(Ministry for the Environment, 2008).
2.
Background: Global Climate Change – Science and Impacts
This section summarises some key findings from the 2007 assessment reports of the
IPCC, as background for the discussion of changes in Tasman District later in this
report.
2.1
The Physical Science Basis (IPCC Working Group I):
The Summary for Policymakers of the Working Group I Report [IPCC, 2007a] makes
the following two points strongly, and summarises the evidence for them:
•
Warming of the climate system is “unequivocal”
•
Most of the observed increase in globally averaged temperatures since the
mid-20th century is very likely (90% probability) due to the increase in
greenhouse gas concentrations caused by human activities.
The full range of projected globally-averaged temperature increases for the SRES
emission scenarios (for 2090-2099 compared to 1980-1999) is 1.1 to 6.4°C, with a
best estimate range of 1.8 to 4.0°C Increasingly severe weather (tropical cyclone
intensity, heatwaves, increases in intense precipitation, heatwaves, drought) is also
projected. Model-based sea-level rise projections for the end of the 21st century range
from 18 to 59 cm, excluding future rapid dynamical changes in ice flow. If such
Climate Change and Variability – Tasman District
2
changes grow linearly with global temperature change, they could increase the upper
range of sea level change by 10 to 20 cm.
Sea ice is projected to shrink in both the Arctic and Antarctic, with projections that
late-summer Arctic sea ice could disappear almost entirely by the end of the Century
under some scenarios. The oceans are also expected to experience further acidification
due to increasing carbon dioxide concentrations. Both past and future anthropogenic
carbon dioxide emissions will continue to contribute to warming and sea level rise for
more than a millennium. If there is a sustained global average warming in excess of
somewhere between 1.9°C and 4.6°C, this may lead eventually (over many hundreds
of years to millennia) to virtually complete elimination of the Greenland Ice Sheet and
a resulting contribution to sea level rise of about 7 m.
2.2
Impacts, Adaptation and Vulnerability (IPCC Working Group 2):
The Working Group 2 Summary for Policymakers (SPM) (IPCC, 2007b) concludes
that many natural systems are being affected by climate changes, particularly
temperature increases. Observational evidence is summarised for this statement from
all the continents and most oceans, and it is concluded these changes are very unlikely
to be due solely to natural variability of temperature or natural variability of the
systems – it is likely that anthropogenic warming has had a discernable influence on
many biological and physical systems. A key figure summarises projected impacts as
a function of increasing global temperature change relative to 1980-99. Projected
impacts include hundreds of millions of people exposed to increased water stress,
increased risk of extinction for approximately 20-30% of plant and animal species
assessed so far if increases in global temperature exceed 1.5°C to 2.5°C, increased risk
of hunger at low latitudes for local temperature increases of even 1 to 2 °C (but
increased total global food production for increases of temperature over a range of 1 to
3°C with a decrease above this), millions more people experiencing coastal flooding
each year for temperature increases above about 2°C, and about 30% of global coastal
wetland lost for temperature rises of above 3°C.
Impacts of climate change will vary regionally, but, aggregated and discounted to the
present, they are very likely to impose net annual costs which will increase over time
as global temperatures increase. Impacts due to altered frequencies and intensities of
extreme weather, climate and sea level events are very likely to change. Some largescale events have the potential to cause very large impacts, especially after the 21st
century.
Climate Change and Variability – Tasman District
3
The SPM states that adaptation will be necessary to address impacts resulting from
even the warming which is already unavoidable due to past emissions, but that more
extensive adaptation than is currently occurring is required to reduce vulnerability to
future climate change. The SPM concludes that a portfolio of adaptation and
mitigation measures can diminish the risks associated with climate change.
2.3
Mitigation of Climate Change (IPCC Working Group 3):
The Working Group 3 Summary for Policymakers (IPCC, 2007c) notes that global
greenhouse gas (GHG) emissions have increased 70% between 1970 and 2004. With
current policies they will continue to grow over the next few decades. However, there
is substantial economic potential for reducing this projected growth rate of GHG
emissions. Technologies include energy efficiency, renewable energy, biofuels, public
transport, nuclear power, carbon capture and storage, land restoration, afforestation,
increased soil carbon storage, and livestock / manure / fertilizer management.
The IPCC report examines emissions pathways that would eventually stabilise
greenhouse gases in the atmosphere at various concentration levels, and the expected
corresponding changes in global temperatures. It concludes that efforts over the next
two to three decades will have a large impact on opportunities to achieve the lower
stabilisation levels considered. For example assessed scenarios which limit eventual
temperature rises to 2.0 to 2.4°C above pre-industrial conditions have 50% to 85%
reductions in emissions (compared to 2000) by 2050, and further reductions thereafter,
reaching “stabilised” carbon dioxide equivalent concentrations (CO2-eq) of 440-490
ppm. Estimated costs in 2030 for multi-gas emission reductions on paths leading to
eventual stabilization at between 445 ppm CO2-eq (eventual temperature increase
about 2°C) and 710 ppm CO2-eq (eventual temperature increase about 4°C) are
estimated at between a 3% decrease in 2030 global gross domestic product and a small
increase, compared to the baseline.
3.
Background: New Zealand Climate Change – Science and Impacts
Published information about the expected impacts of climate change on New Zealand
is summarised and assessed in the Australia and New Zealand chapter of the Working
Group 2 volume of the IPCC’s Fourth Assessment Report (Hennessy et al, 2007).
Key findings from this chapter include:
Regional climate change has already occurred. Since 1950 there has been 0.3 – 0.7 °C
warming across the Australia/NZ region as a whole, with more heat waves, fewer
Climate Change and Variability – Tasman District
4
frosts, more rain in southwest New Zealand, less rain in northeastern New Zealand,
and a rise in sea level of about 70 mm.
We are already experiencing the impacts of climate change: The report states with
“high confidence” that impacts of regional climate change are now evident in
increasing stresses on water supply and agriculture, changed natural ecosystems,
reduced seasonal snow cover, and ongoing glacier shrinkage. Ongoing vulnerability to
extreme events is demonstrated by substantial economic losses caused by droughts,
floods, fire, tropical cyclones, and hail.
New Zealand’s future climate: During the 21st century, New Zealand’s climate is
“virtually certain” [more than 99% probability] to be warmer, with noticeable changes
in extreme events;
•
Heat waves and fire risk are virtually certain to increase in intensity and
frequency.
•
Floods, landslides, droughts and storm surges are likely to become more
frequent and intense, and snow and frost are likely to become less frequent.
•
Large areas of eastern New Zealand are likely to have less soil moisture,
although western New Zealand is likely to receive more rain.
Impacts and Vulnerability: The potential impacts of climate change are likely to be
substantial without further adaptation. Ecosystems, water security, and coastal
communities become vulnerable if global temperature rises by 1.5°C to 2°C, even with
adaptive measures. Energy security, health, agriculture, and tourism have considerable
coping ranges and adaptive capacity, but they become vulnerable if warming exceeds
3.0° C.
3.1
Sectoral Impacts
Natural ecosystems: The structure, evolution and species of many natural ecosystems
are very likely to alter. The impacts of climate change are likely to be significant by
2020, and are virtually certain to:
•
exacerbate existing stresses such as invasive species and habitat loss;
•
increase the probability of species extinctions;
•
degrade many natural ecosystems;
•
reduce ecosystem services for tourism, fishing and water supply.
Climate Change and Variability – Tasman District
5
The report says that actions to reduce non-climatic stresses such as water pollution,
habitat fragmentation, and invasive species can enhance the resilience of many
ecosystems.
Water security: Projections show that drought events are likely to increase in both
frequency and severity in the eastern lowlands of New Zealand. Ongoing water
security problems are very likely to increase by 2030 in those parts of eastern New
Zealand that are distant from major rivers.
The IPCC chapter says that increasing demand for water has already exceeded supply
in some catchments but “ongoing proposed adaptation strategies are likely to buy
some time”.
Coastal Development: Ongoing coastal development is very likely to exacerbate the
future risk to lives and property from sea-level rise and storms:
•
Sea level is virtually certain to rise.
•
By 2050 there is very likely to be increasing loss of high-value land, faster
road degradation, degraded beaches, and loss of landmarks of cultural
significance.
The IPCC chapter says tighter planning and regulation are likely to be required if
continued rates of coastal development are to remain sustainable.
Infrastructure: Risks to major infrastructure are likely to increase markedly. These
risks include failure of flood protection and urban drainage / sewerage systems, and
more storm damage to buildings. The present design criteria for extreme events are
very likely to be exceeded more frequently by 2030. Risks to large structures such as
dams and bridges will need to be reassessed in light of future climate threats.
Tourism: Changes in seasonal snow cover are likely to have a significant impact on
the ski industry. The snow line is likely to rise by 120 – 170m based on scenarios for
the 2080s, but tourist flows from Australia to New Zealand might grow as a result of
the relatively poorer snow conditions there. Noticeable glacier shrinkage and retreat
are likely for even small temperature rises, and likely to reduce visitor flows through
tourism-dependent towns such as Fox and Franz Josef.
Climate Change and Variability – Tasman District
6
Pastoral Farming: In cool areas of New Zealand, annual pasture production may
increase by 2030, although gains may decline thereafter1. Subtropical pasture species
with lower feed quality are likely to spread southwards, reducing productivity,
particularly near Waikato.
The range and incidence of many pests and diseases are likely to increase. Water
security problems are likely to make irrigated agriculture vulnerable. Less cold-stress
is likely to reduce lamb mortality.
Horticulture: Areas suitable for particular crops are projected to change. For example,
production of current kiwi fruit varieties is likely to become uneconomic in Northland
by 2050 because of lack of winter chilling, but more areas in the South Island are
likely to become suitable. New Zealand is likely to be more susceptible to the
establishment of new horticultural pests.
Forestry: In the south and west, growth rates of economically-important plantation
forests (mainly Pinus radiata) are likely to increase, but tree growth reductions may
occur in some drier regions.
Fisheries: Few climate change impact studies have been undertaken, but impacts are
likely to be greater for temperate endemic species than for tropical species, and on
coastal and demersal fisheries relative to pelagic and deepsea fisheries.
Timing: Initially there may be some beneficial effects for New Zealand. Up to about
2050, enhanced growing conditions from higher carbon dioxide concentrations, longer
growing seasons and less frost risk are likely to benefit agriculture, horticulture and
forestry over much of New Zealand provided adequate water is available. But by
2050, agriculture and forestry production is likely to be reduced over parts of eastern
New Zealand due to increased drought and fire. Reduced energy demand is very likely
in winter. Flows in New Zealand’s largest rivers are likely to increase, benefiting
hydroelectric generation and irrigation supply.
These benefits are limited to specific sub-sectors and sub-regions, and are for a global
average temperature increase of about 1-2°C.
1
Further New Zealand research since the IPCC report was published suggests the overall
impacts of climate change on average-year pastoral production summed over all of New
Zealand may be small through the 21st Century, with decreases in some regions offset by
increases in others, and with total national production in “worst” years less than in “worst”
years under the present climate (Stroombergen et al, 2008).
Climate Change and Variability – Tasman District
7
4.
Present Climate
The plains of the Tasman District (de Lisle and Kerr, 1965) are sheltered both from
the prevailing westerly winds and from winds from an easterly quarter, providing a
sunny, mild climate, less windy than most other areas in New Zealand but prone to
frost in sheltered positions. The rainfall, which is adequate for spring pasture growth,
is liable to be insufficient in summer and early autumn when long dry spells can occur.
4.1
Spatial Patterns in Tasman’s Climate
Figure 2 shows the spatial variation in annual temperature over the region. Figure 3
shows the spatial pattern of annual rainfall, and also the median seasonal rainfalls.
Figure 2:
Annual average temperature for the Tasman region (median for 1971 – 2000).
©NIWA.
Climate Change and Variability – Tasman District
8
Figure 3:
Annual rainfall for the Tasman region (top: median for 1971-2000), and seasonal
rainfalls (bottom: medians for spring, summer, autumn and winter). ©NIWA.
Climate Change and Variability – Tasman District
9
4.2
Figure 4:
Temporal Variability in Tasman’s Climate
Homogenised annual temperature time series for Appleby (courtesy of J.
Salinger, NIWA). The smoothed red line2 removes much of the year-to-year
variability, and indicates an upward long-term trend. ©NIWA.
There is significant year-to-year variability in Tasman’s climate. For example, figure 4
is the homogenised3 annual temperature time series for Appleby, a climate station
located between Richmond and Mapua4 (Figure 1). There are substantial year to year
fluctuations in temperature, with some years being nearly 2°C different from others.
These year to year fluctuations appear to be superimposed on a long-term upward
trend in temperature.
The best-fit linear trend to these Appleby temperatures is an increase of 0.73±0.15 °C
between 1908 and 2006. This is similar to the upward trend in temperature averaged
over New Zealand as a whole of 0.9°C between 1908 and 2006 (Ministry for the
Environment, 2008). A likely explanation is that the long-term trend is at least in part
2
The red line is a 13 point filter, with weights of (1, 6, 19, 42, 71, 96, 106, 96, 71, 42, 19, 6,
1)/576
3
Homogenisation describes a process to remove effects of site or instrument changes from the
long-term record.
4
See Figure 1 for locations
Climate Change and Variability – Tasman District
10
due to increasing global concentrations of greenhouse gases, while the shorter period
variability is due to natural causes, such as the El Niño – Southern Oscillation,
together with year-to-year random fluctuations (“climate noise”).
As shown in Figure 5, there is also substantial year to year variation in rainfall. For
example, Appleby exhibits annual rainfall totals ranging from around 600 mm up to
more than 1400 mm, but no marked long-term trend.
Figure 5:
4.3
Annual rainfall at Appleby, 1932 – 2006. ©NIWA.
Natural factors causing fluctuation in climate patterns over New Zealand
Two factors that influence rainfall in New Zealand (Ministry for the Environment,
2008) are the El Niño-Southern Oscillation (ENSO), and the Interdecadal Pacific
Oscillation (IPO).
4.3.1
The effect of El Niño and La Niña
The ENSO is a natural oscillation that may be thought of in terms of a movement back
and forth of warm surface water across the equatorial Pacific Ocean. El Niño events,
when the warm water “spills out” eastwards across the Pacific, occur irregularly, about
Climate Change and Variability – Tasman District
11
3 to 7 years apart, typically becoming established around April or May and persisting
for about a year thereafter. The La Niña phase shows essentially the opposite
behaviour in the tropical Pacific, with cooler surface water in the eastern equatorial
Pacific. The upper panel of Figure 7 shows a time series of the Southern Oscillation
Index (SOI), a common measure of the intensity and state of ENSO events derived
from the pressure difference between Tahiti and Darwin. Persistence of the SOI below
about -1 coincides with El Niño events, and periods above +1 with La Niña events.
Figure 6:
Time series of Southern Oscillation Index (upper panel) and Interdecadal Pacific
Oscillation (lower panel) from 1900. ©NIWA.
Differences between El Niño and La Niña periods are seen most clearly in the tropics,
but there are also related changes in New Zealand rainfall and temperature patterns.
The general pattern during El Niño events is for New Zealand to experience stronger
than normal southwesterly airflow, lower than average seasonal temperatures, and
drier than normal conditions in the northeast of the country. During La Niña
conditions New Zealand generally experiences more northeasterly flows, higher
temperatures, and wetter than normal conditions in the north and east of the North
Island. Figure 6 shows average summer rainfall anomalies in New Zealand associated
Climate Change and Variability – Tasman District
12
with El Niño and La Niña conditions. However, individual ENSO episodes can differ
substantially from these average patterns.
Figure 7:
ENSO composite rainfall anomalies (in %) for summer (December-February),
for the 10 strongest events 1960-2007 for New Zealand. (The insert boxes indicate
the years used, where 1964 is December 1963 to February 1964, etc). ©NIWA.
From Figure 7 it can be seen that on average summer rainfall for most of the fertile
plains adjacent to Tasman Bay (e.g. Motueka, Waimea) is less than normal during El
Niño periods and more than normal during La Niña periods.
4.3.2
The effect of the Interdecadal Pacific Oscillation.
The Interdecadal Pacific Oscillation, or IPO, is a natural fluctuation associated with
decadal climate variability over parts of the Pacific Ocean, which has also been found
to influence some aspects of climate over parts of Australia and New Zealand
(Salinger et al., 2001). A time series of the IPO, derived from a UK Met Office
analysis of global sea surface temperature patterns, is shown in the lower panel of
Figure 6. Around New Zealand, sea surface temperatures tend to be lower, and
westerly winds stronger, during the positive phase of the IPO.
Climate Change and Variability – Tasman District
13
Long-lived fluctuations in New Zealand climate show some association with IPO
changes (this is a general “on average” behaviour, and does not mean every year of a
positive IPO behaves in a particular way). An increase in New Zealand’s annual
average temperatures around 1950 occurred shortly after the change from positive to
negative phase IPO (Figure 6), and the switch from negative to positive IPO in the late
1970s coincided with significant rainfall changes (Ministry for the Environment,
2008). Figure 8 maps annual rainfall changes between negative and positive IPO
periods centred on 1978.
Figure 8:
Percentage change in average annual rainfall, for the 1978-1998 period compared
to the 1960-1977 period. (Note: From 1978-98 the IPO was in its positive phase,
compared to the previous 18 years when the IPO was negative. Any local rainfall
response due to global warming would also be contained within this pattern of rainfall
trends). ©NIWA.
Figure 8 suggests that periods of positive IPO tend to be a little drier than average for
most of the fertile plains adjacent to Tasman Bay (e.g. Motueka, Waimea). A recently
published paper by Griffiths (2006) indicates that for the period from 1930-2004, a
trend to decreases in mean (and extreme 1-day rainfall) and increasing dry spell
duration, was generally seen in the north and east of both the South and North
Islands5. Griffiths suggests this results from a trend to increased westerly circulation
across New Zealand between 1950 and 2004. She says this is consistent with the
5
The opposite behaviour – ie a trend to increases in mean and extreme rainfall – was observed
to the west of a line from Westport to Invercargill.
Climate Change and Variability – Tasman District
14
enhanced warming since 1950 (as predicted by climate change modelling); the
)
stronger
IPO westerly phase since 1977; the increased frequency of El Niño events
m
c 1977; or a mixture of all these considerations.
since
(
4.4
9
9
New
8
1
Zealand Sea Level Trends and Variability
Around
New Zealand, sea level has been rising (after a period of relative stability)
e
c
since
n the early to mid part of the 1880s, with a historic rate of rise of approximately
i
0.16m
over the past 100 years up to the year 2000 (Figure 9, Ramsay and Wild 2008).
s
This lies within the range of global sea level rise observed over the 20th century of
e
0.17
s ± 0.05 metres (Bindoff et al., 2007).
i
r
l
e
v
e
l
a
e
s
e
v
i
t
a
l
e
R
Trends in relative sea-level rise at Auckland, Wellington, Lyttelton
Sources: Ports of Auckland Ltd., Hannah (2004), NIWA
25
20
15
10
5
Auck AMSL
Auckland trend
Wellington trend
Lyttelton trend
0
-5
1900
1920
1940
1960
1980
2000
Year
Figure 9:
Annual mean sea-level data from the Port of Auckland (Waitemata Harbour) up
to 2005, which represents the longest, most consistent record in New Zealand.
Trend lines in relative sea-level rise since 1899 calculated from data measured at
Auckland (1899–1999), Wellington (1899–2001 with gaps), Lyttelton (1901–2001
with gaps). (Ramsay and Wild, 2008). ©NIWA.
While the long term trend in New Zealand sea level rise is consistent with global
climate change, Figure 9 indicates that (as with rainfall and temperature) there are also
shorter term fluctuations. Seasonal (annual), El Niño/Southern oscillation (ENSO, 3-7
year) and Interdecadal Pacific Oscillation (IPO, 20-30 year) variations can cause
fluctuations of up to about ±0.25m in background sea levels for short periods. For
example during El Niño phases, sea levels tend to be depressed, and during La Niña
phases sea levels tend to be higher. The IPO in its negative phase (the phase at the
Climate Change and Variability – Tasman District
15
time of writing this report, i.e. 2008) tends to increase sea levels around the North
Island by around 0.06m above the background sea-level rise.
Also storm surge can temporarily increase sea level over 1-3 days. Storm surge is due
to a reduction in atmospheric pressure (inverse barometer effect) and the influence of
wind on the sea surface. In a New Zealand context, maximum storm surge on the open
coast is unlikely to be more than about 1 m, but can be higher in estuarine and harbour
settings, Wave conditions also affect localised water levels where inshore of the wave
breaker zone, water levels are set-up. This is a localised phenomenon and can be
highly variable along even a short stretch of coastline, being dependent on the wave
conditions and configurations of offshore sandbars and beach slope.
5. Projections of Tasman’s Future Climate
The future climate of the Tasman District is expected to result from a combination of
the effects of anthropogenic climate change resulting from increasing global
concentrations of greenhouse gases (Section 2), plus the natural year-to-year and
decade-to-decade variability resulting from “climate noise” and features such as the El
Niño – Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO)
discussed in Section 4. The present section first outlines the projected changes due to
anthropogenic climate change, and then returns to the issue of natural variability.
Predicting future changes in climate due to anthropogenic activity is made difficult
because (a) they depend on future greenhouse gas concentrations, which in turn
depend on global greenhouse gas emissions driven by factors such as economic
activity and policies for sustainable resource use, and (b) even for a specific future
trajectory of global greenhouse gas emissions, different climate models predict
somewhat different amounts of climate change.
This has been dealt with by the Intergovernmental Panel on Climate Change through
consideration of “scenarios” describing emissions for a range of possible economic,
political and social developments during the 21st century, and by considering results
from several different climate models for a given emissions scenario.
NIWA has used climate model data from the IPCC Fourth Assessment (IPCC, 2007a)
to update climate change scenarios for New Zealand, through a regional downscaling
process described in an updated guidance manual prepared for the Ministry for the
Environment (Ministry for the Environment, 2008). In the present report we show
maps of projected climate changes for the Tasman region under the mid-range IPCC
emissions scenario known as A1B. For the purpose of sensitivity analysis, we also
Climate Change and Variability – Tasman District
16
consider the lowest IPCC emissions scenario (known as B1) and the highest emission
scenario (A1FI). Note that none of the IPCC emissions scenarios assume global
policy actions to specifically reduce greenhouse gas emissions.
Figure 10 indicates the range of global temperature increases projected out to 2100 by
the IPCC for a set of “marker” scenarios spanning their emission scenario range. The
shading and bars for individual scenarios indicate variations between differing global
climate models. The temperature increase at 2100 relative to the average over 19801999 varies from +1.1°C (least sensitive model combined with the lowest emissions
scenario B1) to +6.4°C (most sensitive model with the highest emissions scenario
A1FI). The multi-model average of the temperature increase for the mid-range A1B
scenario is +2.8°C.
Figure 10:
5.1
IPCC projections of global temperature increase. Solid coloured lines are multimodel global averages of surface warming (relative to 1980-1999) for emission
scenarios B1, A1B and A2, shown as continuations of the 20th century
simulations (black line). The coloured shading denotes the ±1 standard deviation
range of individual model annual averages. The grey bars at right indicate the
best estimate (solid horizontal line within each grey bar) and the ‘likely range’
across 6 scenarios that span the full range of all IPCC emission scenarios.
(Adapted from Figure SPM-5, IPCC 2007a).
Tasman Climate Change Temperature Projections
Temperature change projections show little spatial variation across New Zealand, but
the magnitude of the projected change varies with the emissions scenario and also
Climate Change and Variability – Tasman District
17
with the climate model used. Figure 11 shows the seasonal patterns of projected
temperature increase over the upper South Island at 2040 for the A1B emission
scenario, where the temperature changes of 12 global climate models have been
averaged together. Figure 12 shows corresponding patterns for 2090. These nominal
years represent the mid-points of bi-decadal periods: 2040 is the average over 20302049, and 2090 the average over 2080-2099, relative to the baseline climate of 19801999 (denoted as 1990 for short).
Figure 11:
Projected seasonal temperature changes at 2040 (2030-2049 average), relative to
1990 (1980-1999 average), for the IPCC A1B emission scenario, averaged over 12
climate models. ©NIWA.
Climate Change and Variability – Tasman District
18
Figure 12:
Projected seasonal temperature changes at 2090 (2080-2099 average), relative to
1990 (1980-1999), for the IPCC A1B emission scenario, averaged over 12 climate
models. ©NIWA.
Figures 11 and 12 show projected future warming in the Tasman District of
approximately 0.2°C per decade for the A1B emissions scenario, when averaged over
the 12 global climate models analysed by NIWA. A slight acceleration in warming is
projected for the second 50 years of the 21st century compared to the first 50 years.
Some models give less warming and others a faster rate of warming. (Ministry for the
Environment, 2008). The full range of model-projected warming is given in Table 1.
The temperature ranges are relative to the baseline period 1980-1999 (as used by
IPCC), denoted for short as “1990”. Hence the projected changes at 2040 and 2090
should be thought of as 50-year and 100-year trends.
Climate Change and Variability – Tasman District
19
Table 1:
Period
Spring
Summer
Autumn
Winter
Annual
2040
0.7 [0.1, 1.8]
1.0 [0.2, 2.2]
1.0 [0.2, 2.3]
0.9 [0.2, 2.0]
0.9 [0.2, 2.0]
2090
1.7 [0.3, 4.6]
2.2 [0.9, 5.6]
2.1 [0.6, 5.1]
2.0 [0.5, 4.9]
2.0 [0.6, 5.0]
Projected changes in seasonal and annual mean temperature (in °C) for the
Tasman District for 2040 and 2090. The first number is a “mid-range”
projection, with the bracketed numbers giving the lower and upper limits.
©NIWA.
The “mid-range” projection in Table 1 is the temperature increase averaged over all 12
global climate models analysed by NIWA, and also averaged over the six illustrative
emissions scenarios used by the IPCC. The lower limit to warming is set by the
climate model with the lowest climate sensitivity (i.e. least warming) run under the
lowest emissions scenario (B1). The upper limit is set by the most sensitive climate
model under the highest emissions scenario (A1FI).
The IPCC is reluctant to state whether any of their emissions scenarios are more likely
to eventuate than others. However, observed emissions are already increasing faster
than the lowest (B1) scenario, and the slowest temperature increase to 2100 projected
by the B1 scenario is less than the linear extrapolation of the observed New Zealand
temperature increase over the 20th century. Thus, it is the opinion of NIWA scientists
that the actual temperature increase this century is very likely to be more than the
“low” scenario given here. Under the mid-range scenario for 2090, an increase in
mean temperature of 2.0°C would represent annual average temperatures in coastal
Tasman in 2090 similar to those currently experienced in the coastal Bay of Plenty.
5.2
Projections for Frosts and Hot Days under Climate Change
Daily temperature extremes (overnight minimum and daily maximum) are also
expected to vary with regional warming. Two of the IPCC scenarios (B2 and A2) have
so far been run using the NIWA regional climate model. For 2090, these simulations
suggest a substantial decrease in the annual number of frost days in the South Island,
with perhaps 10-20 fewer frost days in the coastal plains of the Tasman District. They
also suggest more days on which the maximum temperature rises above 25°C –
around 20 more days per year in the coastal plains of Tasman District for the B1
scenario and around 40 more days for the A2 scenario (Ministry for the Environment,
2008).
Climate Change and Variability – Tasman District
20
5.3
Tasman Climate Change Rainfall Projections
Rainfall projections show much more spatial variation than the temperature
projections. Again, the magnitude of the projected change will scale up or down with
the emissions scenario, and will also differ between climate models. Figures 13 and 14
show the projected seasonal patterns of precipitation (rain + snow) change over the
Tasman District at 2040 and 2090 for the A1B emissions scenario. As with figures 11
and 12, the changes from the 12 global models have been averaged together.
Figure 13:
Projected seasonal precipitation changes (in %) at 2040 (2030-2049 average),
relative to 1990 (1980-99 average), for the IPCC A1B emission scenario, averaged
over 12 climate models. ©NIWA.
Climate Change and Variability – Tasman District
21
Figure 14:
Projected seasonal precipitation changes (in %) at 2090 (2080-2099 average),
relative to 1990 (1980-99 average), for the IPCC A1B emission scenario, averaged
over 12 climate models. ©NIWA.
The 12-model average projections indicate slightly more rainfall in most seasons
except spring for much of the area of coastal plains adjacent to Tasman Bay (i.e.
Motueka, Waimea plains). From these 12-model averages the western part of Tasman
District is projected to experience slightly less rainfall in summer (by less than 5%),
but significantly more rainfall in winter, especially by 2090. Table 2 shows projection
values with lower and upper limits for a grid point in Nelson obtained from the 12
models across all six illustrative IPCC scenarios.
The average picture hides significant variations between individual models on the
projected seasonal rainfall changes. Figure 15 shows seasonal rainfall projections from
all the models individually for the Nelson grid-point for 2090. For this location,
although the models disagree on the projected magnitude of change, most agree in
Climate Change and Variability – Tasman District
22
projecting an increase in summer, autumn, and winter. Either increases or decreases
appear almost equally likely in spring.
Period
Spring
Summer
Autumn
Winter
Annual
2040
0 [-8, 9]
4 [-14, 27]
5 [-2,19]
1 [-4, 9]
2 [-3, 9]
2090
-1[-20,19]
6 [-13, 30]
5 [-4, 18]
6 [-2,19]
4 [-3,14]
Table 2:
Projected changes in seasonal and annual mean rainfall (in %) for the Nelson
grid point for 2040 and 2090. The first number is the “mid range” estimate, with
bracketed numbers giving the lower and upper limits.
Figure 15:
Projected seasonal precipitation changes by 2090 for Nelson grid point, for the
A1B scenario. The vertical coloured bars show the range over all climate models
used, and stars the projected changes for each model individually. ©NIWA.
5.4
Scenarios for Changes in Extreme Rainfall
A warmer atmosphere can hold more moisture (about 8% more for every 1°C increase
in temperature), so there is a potential for heavier extreme rainfall under global
warming. The IPCC in its Fourth Assessment Report concluded that the frequency of
heavy precipitation events (or proportion of total rainfall from heavy falls) is “very
Climate Change and Variability – Tasman District
23
likely” to increase over most areas (Solomon et al., 2007, Table TS.4). Given the
mountainous nature of New Zealand, spatial patterns of changes in rainfall extremes
are expected to depend on changes in atmospheric circulation and storm tracks.
Preliminary analyses carried out with the NIWA regional climate model for the B2
and A2 emission scenarios indicate that for extremes with return periods of 30 years
and longer, the simulated increase in rainfall depth was approximately 8% per degree
of local warming, when averaged over the whole country. However these modelled
changes were not geographically uniform.
ARI
(yrs)
Table 3:
Duration
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
7.5
14.4
20.7
28.3
46.5
57.2
72.8
87.4
97.9
5
10.8
19.9
28.1
37.8
61.4
74.9
95.0
114.1
128.6
10
13.6
24.2
33.8
45.0
72.3
87.7
110.7
132.7
149.6
20
16.6
28.9
39.8
52.5
83.8
100.8
126.6
151.2
170.1
30
18.6
31.9
43.7
57.2
90.8
108.7
136.1
162.2
182.1
50
21.3
36.0
48.8
63.5
100.0
119.1
148.4
176.3
197.4
100
25.6
42.0
56.4
72.6
113.3
134.0
165.7
195.8
218.4
Current rainfall depth-duration-frequency statistics for Richmond from HIRDS
V2.0 (Thompson, 2002). Numbers in the body of the table are in millimetres
NIWA has produced some updated guidance on changes in heavy rainfall to be used
for “screening assessments”6 in New Zealand, for the 2008 update to the Local
Government Guidance manual (Ministry for the Environment, 2008). An overview of
the process for producing heavy rainfall statistics for screening analyses, with a
detailed example of its application for Richmond, is provided in the appendix to the
present report. The recommendation in the Local Government Guidance manual is that
if a screening analysis using statistics produced through this process indicates changes
in heavy rainfall could lead to problems for a particular asset or activity, then further
guidance should be sought from a science provider for a more detailed risk analysis.
Rainfall depth-duration-frequency statistics for Richmond under current conditions are
provided in Table 3. Statistics for screening studies under mid-range temperature
change scenarios for 2040 and 2090 are provided in Tables 4a and 4b.
6
“Screening” describes an initial assessment step to consider whether potential impacts of
climate change on a particular function or item of infrastructure are likely to be material
Climate Change and Variability – Tasman District
24
ARI
(yrs)
Table 4(a):
Duration
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
8
15
22
30
49
60
76
90
101
5
12
21
30
40
65
79
100
119
134
10
15
26
36
48
77
93
117
140
158
20
18
31
43
56
89
107
135
161
181
30
20
34
47
61
97
117
146
174
195
50
23
39
52
68
107
128
159
189
212
100
27
45
60
78
121
144
178
210
234
Projected rainfall depth-duration-frequency statistics for Richmond in 2040, for
a mid-range temperature scenario (0.9°C warming)
ARI
(yrs)
Table 4(b):
Duration
10m
30m
60m
2h
6h
12h
24h
48h
72h
2
9
16
23
32
51
63
79
94
105
5
13
23
32
43
69
84
105
126
141
10
16
28
39
51
82
99
125
149
167
20
19
33
46
60
96
116
145
173
194
30
22
37
51
66
105
126
158
188
210
50
25
42
57
74
116
138
172
205
229
100
30
49
65
84
131
155
192
227
253
Projected rainfall depth-duration-frequency statistics for Richmond in 2090, for
a mid-range temperature scenario (2.0°C warming)
Projected rainfall depth-duration-frequency tables for other locations in Tasman
District can be produced using the HIRDS software package and the process
illustrated in the Appendix and described in the revised Local Government Guidance
Manual (Ministry for the Environment, 2008).
Climate Change and Variability – Tasman District
25
5.5
Evaporation, Soil Moisture and Drought
A NIWA study published in 2005 (Mullan et al, 2005) used downscaled climate model
results from the IPCC Third Assessment to examine how the frequency of very dry
conditions could change over the coming century. Two particular scenarios were
highlighted: a “low-medium” scenario coupling an IPCC emissions scenario having a
relatively low global temperature increase projection with a downscaled climate model
having a relatively small change in the west-east annual rainfall pattern; and a
“medium-high” scenario which couples a higher global temperature change projection
with a downscaled model in which the west-east rainfall ratio changes significantly
(with less rain in the east).
The 2005 study concluded that drought risk is expected to increase during this century
in all areas that are currently drought prone, under both the “low-medium” and the
“medium high” scenarios (the drought risk is analysed in terms of July-June growing
year accumulated values of Potential Evapotranspiration Deficit (PED)7). Detailed
maps of the predicted future recurrence interval of the driest conditions which
currently occur on average once every 20 years suggest that such droughts could occur
on average once every 10 to 15 years under the “low-medium” scenario, and more
than twice as frequently for the “medium-high” scenario, for the coastal plain areas
adjoining Tasman Bay (e.g. Motueka and Waimea plains).
NIWA scientists intend to repeat this drought analysis using downscaled model results
from the IPCC’s latest (Fourth) assessment. Until such work is completed, the best
guidance we can provide is that there is a risk that the frequency of drought (in terms
of low soil moisture conditions) could increase as the century progresses, for the main
agriculturally productive parts of Tasman District.
5.6
Wind
Some broad scale analyses have been undertaken (Ministry for the Environment,
2008) of how the seasonal and annual westerly and southerly components of the flow
across New Zealand could change by 2040 and 2090, based on climate model results
from the IPCC Fourth Assessment Report. These suggest an overall increase in the
annual mean westerly component of the flow across New Zealand. A strong
seasonality is apparent within this annual picture, with increases in the westerly
component in winter and spring and decreases in summer and autumn (this is the
behaviour from averaging results from 12 different climate models run for the A1B
7
Accumulated PED is the amount of water that would need to be added to a crop over a year to
prevent loss of production due to water shortage.
Climate Change and Variability – Tasman District
26
scenario – there is a range of behaviour across individual models. More details are
given in the revised Local Government Guidance Manual (Ministry for the
Environment, 2008).
An increase in the mean westerly component of the wind does not in itself necessarily
imply an increase in total wind speed, or in wind speed extremes. However some very
initial work with the NIWA regional climate model (Ministry for the Environment,
2008) suggests there could be a relatively small increase in the strongest winds over
much of the country by 2100 (averaging out at a 2.3% increase over the land points in
the model).
We conclude that there has not yet been enough research and modelling undertaken to
allow a confident projection of how extreme wind speeds might change over the
Tasman District, but that a small increase cannot be ruled out by 2100.
5.7
Climate Change and Sea Level 8
Sea levels will continue to rise over the 21st century and beyond primarily because of
thermal expansion within the oceans and loss of ice sheets and glaciers on land. The
basic range of projected global sea-level rise estimated in the IPCC’s Fourth
Assessment Report (IPCC 2007a) is for a rise of 0.18 m to 0.59 m by the decade 20902099 (mid 2090s) relative to the average sea level over the period 1980 to 1999, as
shown in Figure 16. This is based on projections from 17 different Global Climate
Models (GCMs) for six different future emission scenarios. The ranges for each
emission scenario are 5 to 95% intervals characterising the spread of GCM results
(bars on the right-hand side of Figure 16). However, these projections exclude
uncertainties in carbon-cycle feedbacks and the possibility of faster ice melt from
Greenland and West Antarctic Ice Sheets.
8
Much of the material in this section is taken from a draft report by Ramsay and Wild [2008]
under preparation for the Tasman District Council
Climate Change and Variability – Tasman District
27
Figure 16:
Global mean sea-level rise projections to the mid 2090s in the context of historical
sea-level measurements back to 1870. The black line and grey shading on the left
hand side show the decadal-averaged global sea levels and associated uncertainty
respectively, as measured by tide gauges throughout the world. The red line is the
decadal averaged sea levels as measured by satellites since 1993. The green line is
the mean annual relative sea level as measured at the Port of Auckland since
1899 (New Zealand’s longest tide gauge record). The light blue shading shows the
range in projected mean sea level out to the 2090s. The dark blue line shows the
potential additional contribution from Greenland and West Antarctic Ice Sheets
if contributions to sea-level rise were to grow linearly with global average
temperature change. The vertical colour lines on the right-hand side show the
range in projections from the various GCMs for six emission scenarios. ©NIWA.
The basic set of projections (light blue shading in Figure 16) include sea-level
contributions due to ice flow from Greenland and West Antarctic Ice Sheets at the
rates observed between 1993 to 2003 but it is expected that these rates will increase in
the future particularly if greenhouse gas emissions are not reduced. An additional 0.1
to 0.2 m rise in the upper ranges of the emission scenario projections (dark blue
shading) would be expected if these ice sheet contributions were to grow linearly with
global temperature change. An even larger contribution from these ice sheets,
especially from Greenland, over this century cannot be ruled out.
Climate Change and Variability – Tasman District
28
A revised guidance manual for local government on coastal hazards and climate
change is currently in preparation, under contract to the Ministry for the Environment.
This will include updated guidance on changes in mean sea level for use in future
planning and decisions. Numbers for use in such guidance depend on risk
management considerations as well as scientific assement, and are currently the
subject of discussion with experts from the engineering, local government, and
insurance sectors, and with scientists. We recommend that Tasman District Council
use this new updated guidance from the Ministry for the Environment once it is
finalised and disseminated. For the interrim, our provisional suggestions are:
1 For planning and decision timeframes out to the 2090’s (2090-2099) use:
•
a base mean sea-level rise of 0.5 m relative to the 1980-1999 average,
along with;
•
an assessment of the sensitivity of the issue under consideration to
possible higher mean sea-levels taking account of possible additional
contributions9. This level is currently under discussion, but is likely to be
no less than 0.8 m.
2 For planning and decision timeframes beyond 2100 where, as a result of the
particular decision, future adaptation options will be limited, an allowance for
mean sea-level rise of 10 mm/year beyond 2100 is recommended (in addition
to the above recommendation).
These projections are for mean sea levels. Less information is available on how
extreme storm sea levels will change with climate change. This will largely depend on
changes in frequency, intensity and/or tracking of atmospheric low-pressure systems,
and occurrence of stronger winds, but there remains uncertainty as to how climate
change will influence such extreme events. As such it is assumed that storm tide
elevation will rise at the same rate as mean sea-level rise until future projections of
changes in storminess become more certain.
9
Possible extra contributions include higher emission scenarios, and uncertanties associated
with increased contributions from Greenland and Antarctica ice sheets, carbon cycle feedbacks,
and possible differences from global averages in the New Zealand region.
Climate Change and Variability – Tasman District
29
5.7.1
Figure 17:
Effect of Sea-Level Rise on High Tide Exceedance Frequency
The frequency of occurrence of high tides exceeding different present day tide
marks for the present (heavy line), 0.18m of sea level rise (lower red line) and
0.59 m of sea level rise (upper red line) for Tarakohe (top) and Little Kaiteriteri
(bottom). ©NIWA.
Terminology used in Figure 17 includes:
MLOS: Mean Level of the Sea
Max: Maximum expected in 100 years (2000-2099) excluding climate and meteorological
effects. (Also called Highest Astronomical Tide)
MHWPS: Mean High Water at Perigean Spring
MHWS: Mean High Water Spring
MHWS-12: A definition of MHWS based on 12% of high tides exceeding this level
MHWN: Mean High Water Neap
MHWAN: Mean High Water at Apogean Neap
Definitions of most of these terms are provided on the Proudman Oceanographic Laboratory
web page at http://www.pol.ac.uk/ntslf/tgi/definitions.html. Terms not explained there include:
Climate Change and Variability – Tasman District
30
Perigean Spring Tides: These occur when a full or new moon coincides with perigee, the point
of closest approach of the moon to the earth. Likewise, apogee is when the moon is at its
furthest point from the earth.
An example of the effect that future sea-level rise has on the frequency of high tides at
Tarakohe and Little Kaiteriteri is shown in Figure 17. For each plot the black line
shows the percentage of high tides that exceed certain levels above mean level of the
sea for present day sea-levels. If we consider the Mean High Water Perigean Spring
(MHWPS) level, at Tarakohe this is exceeded by about 3.5% of high tides. The
coloured lines show this occurrence with different future sea level rises (0.18m and
0.59 m). For a sea-level rise of 0.18 m, a present day MHWPS level would be
exceeded by 12% of the high tides at Tarakohe and by 48% with a sea-level rise of
0.59 m.
5.8
Climate Change Impacts on Other Coastal Hazard Drivers
There has been little progress, both globally and in New Zealand since the IPCC Third
Assessment Report in 2001, in understanding the effects climate change is having, and
will have, on the other drivers of coastal hazards, such as tides in shallow waters,
storms, waves, swell and coastal sediment supply.
Whilst it is expected that the intensity of severe storms may increase, there is still
much uncertainty associated with how future climate change will influence the
frequency, intensity and tracking of tropical cyclones (in the Pacific tropics), extropical cyclones (which track down to the temperate regions such as New Zealand),
mid-latitude extra-tropical cyclones and low-latitude storms.
There is a reasonable level of confidence that winter atmospheric pressure gradients
will increase over the South Island implying an increase in mean westerly-wind
component of flows across New Zealand expected by 2090s (and hence changes in
wave climate on west facing coastlines). Climate model downscaling to New Zealand
shows this shift in bias to winds more often coming from a westerly direction but
overall wind speeds in all directions may not change significantly.
5.9
Considering both Anthropogenic and Natural Changes
Much of the material in Sections 5.1 to 5.8 focuses on the projected impact on the
climate of Tasman District over the coming century of increases in global
anthropogenic greenhouse gas concentrations. But natural variations, such as those
described in Section 4.2 (associated with for example El Niño, La Niña, the
Interdecadal Pacific Oscillation, and “climate noise”), will also continue to occur. As
Climate Change and Variability – Tasman District
31
noted at the beginning of Section 5, those involved in (or planning for) climatesensitive activities in the Tasman District will need to cope with the sum of both
anthropogenic change and natural variability.
An example of this for temperature (from an overall New Zealand perspective) is
shown in Figure 18. In this figure the annual bars represent deviations from the 198099 New Zealand average temperature (red for positive deviations). The bars up to
2006 are the annual averages of data from seven long-term NIWA climate stations
distributed over the country. The bars after 2006 are New Zealand averages of yearby-year downscaled temperatures from one of the IPCC Fourth Assessment Report
models which simulated natural year-to-year variability together with long-term trends
resulting from anthropogenic greenhouse gas emissions.
Figure 18 should not be interpreted as a set of specific predictions for individual years.
But it illustrates that although we expect a long term overall upward trend in
temperatures, there will still be some relatively cool years. However for this particular
example, a year which is unusually warm under our present climate could become the
norm by about 2050, and an “unusually warm” year in 30-50 years time is likely to be
warmer than anything we currently experience.
Figure 18:
New Zealand Temperature, - historical record and an illustrative schematic
projection illustrating future year-to-year variability. (See text for full
explanation)
For rainfall, the fact that we have apparently recently moved into a negative phase of
the Interdecadal Pacific Oscillation (Figure 7, lower panel) may be just as important
for the Tasman region over the next 2-3 decades as the effects of anthropogenic
Climate Change and Variability – Tasman District
32
climate change. From Section 4.2.2, periods of negative SOI may on average
experience slightly above normal rainfall in the coastal plains areas fringing Tasman
Bay, pushing rainfall in these directions in the same direction as expected from
anthropogenic factors (section 5.2). A subsequent further reversal of the IPO in 20-30
years time could have the opposite effect, offsetting part of the anthropogenic trend in
rainfall for a few decades.
As discussed in Section 4.3, the IPO and the El Niño / La Niña cycle have an effect on
New Zealand sea level. So the sea levels we experience over the coming century will
also result from the sum of anthropogenic trend and natural variability.
The message from this section is not that anthropogenic trends in climate can be
ignored because of natural variability. In the projections we have discussed these
anthropogenic trends become the dominant factor locally as the century progresses.
But we need to bear in mind that at some times natural variability will be adding to the
human induced trends, while at others it may be offsetting part of the anthropogenic
effect.
6. Tasman District – Impacts, Vulnerability and Adaptation
The main purpose of this report has been to draw together existing information on how
Tasman’s climate may change in future. The resourcing did not extend to undertaking
a detailed evaluation of the likely impacts of these changes, of the vulnerability of the
Tasman District to these impacts, or of investigating options for adapting to them.
Ways in which councils can investigate some of these issues are outlined in the
updated guidance manual published recently by the Ministry for the Environment
(Ministry for the Environment, 2008), which can be accessed through the Ministry’s
web pages 10. The Ministry for the Environment website also contains links11 to Quality
Planning material that describes ways to address Section 7(i) of the Resource
Management (Energy and Climate Change) Amendment Act 2004. (Section 7(i)
requires particular regard to be given to the effects of climate change).
The Ministry for the Environment guidance material recommends that councils should
build consideration of climate change into their planning activities (“mainstreaming”)
rather than considering them in isolation, and should take a risk management
approach. An overview of some of these issues, with a particular focus on water, is
10
http://www.mfe.govt.nz/publications/climate/climate-change-effect-impacts-assessmentsmay08/climate-change-effect-impacts-assessment-may08.pdf
11
http://www.qp.org.nz/plan-topics/climate-change.php
Climate Change and Variability – Tasman District
33
provided by Wratt et al. (2006). As illustrated by Figure 19, consideration of climate
change becomes particularly important for designing climate-sensitive infrastructure
or assets which are likely to be around for many decades, and for resource use and
land development planning over similar timescales.
Figure 19:
Time scales and adaptation. Planning for human-induced climate change
becomes increasingly important as one moves to the right along this line. (Based
on McInnes et al, 2002).
Some particular impact, vulnerability and adaptation issues to which Tasman District
Council may wish to give consideration include:
•
Implications of sea level rise and coastal change for planning and
development in coastal areas.
•
Implications of potential changes in rainfall and of drought frequency for
water demand, availability and allocation (including planning for irrigation
schemes and storage).
•
Implications of projected changes in extreme rainfall, erosion risk and coastal
hazards for council roading and stormwater drainage infrastructure, lifelines
planning, and civil defence and emergency management.
Climate Change and Variability – Tasman District
34
7.
•
Opportunities which climate change may bring for new horticultural crops –
and infrastructure and land-use issues this might arise.
•
Implications of climate change (including potential changes in flood
frequency and in coastal hazards) for land use planning.
•
Implications for aquaculture and fisheries. Not a lot is known about this, but
Willis et al. (2007) provides a useful starting point.
•
Implications for natural ecosystems and their management, both terrestrial
(see Section 11.4.2 of Hennessey et al, 2007) and marine (Willis et al, 2007).
This is especially relevant given the three National Parks in the region, and the
identification in Chapter 11 if the latest IPCC Working Group 2 assessment
(Hennessey et al., op. cit.) of the vulnerability of some mountain ecosystems
and species.
•
Building consideration of climate change impacts and adaptation into council
planning as outlined in MFE Guidance. Also consultation and discussion with
stakeholders (e.g. groups of farmers) to help them identify climate-related
risks and ways of building resilience. (Kenny, 2005).
References
Bindoff, N.L., J. Willebrand, V. Artale, A, Cazenave, J. Gregory, S. Gulev, K.
Hanawa, C. Le Quéré, S. Levitus, Y. Nojiri, C.K. Shum, L.D. Talley and A.
Unnikrishnan, 2007: Observations: Oceanic Climate Change and Sea Level. In:
Climate Change 2007: The Physical Science Basis. Contribution of Working Group
I to the Fourth Assessment Report of the Intergovernmental Panel on Climate
Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.
Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United
Kingdom and New York, NY, USA.
De Lisle, J.F. and I.S. Kerr. 1965: The climate and weather of the Nelson region, New
Zealand. Misc Pub. 115(3), New Zealand Meteorological Service, Wellington.
10pp.
Griffiths, G.M., 2006: Changes in New Zealand daily rainfall extremes 1930 – 2004.
Weather and Climate 27, 3-44.
Hennessy, K., B. Fitzharris, B.C. Bates, N. Harvey, S.M. Howden, L. Hughes, J.
Salinger and R. Warrick, 2007: Australia and New Zealand. In: Climate Change
Climate Change and Variability – Tasman District
35
2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to
the Fourth Assessment Report of the Intergovernmental Panel on Climate Change,
M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson,
Eds., Cambridge University Press, Cambridge, UK, 507-540.
IPCC, 2007a: Summary for Policymakers. In: Climate Change 2007: The Physical
Science Basis. Contribution of Working Group 1 to the Fourth Assessment Report
of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M.
Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds)].
Cambridge University Press, Cambridge, United Kingdom and New York, NY,
USA.
IPCC, 2007b: Summary for Policymakers. In: Climate Change 2007: Impacts,
Adaptation and Vulnerability. Contribution of Working Group II to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change [M.L.
Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, (eds)].
Cambridge University Press, Cambridge, United Kingdom and New York, NY,
USA.
IPCC, 2007c: Summary for Policymakers. In: Climate Change 2007: Mitigation.
Contribution of Working Group III to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change [B. Metz, O.R. Davidson, P.R.
Bosch, R. Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA.
Kenny, G., 2005: Adapting to Climate Change in Eastern New Zealand: A farmer
perspective.
Earthwise Consulting
Ltd,
Hastings. 148pp
+ CD.
www.earthlimited.org/accenz.html.
McInnes, K.L., R. Suppiah, P.H. Whetton, K.J. Hennessey and R.N. Jones, 2002.
Climate Change in South Australia. CSIRO Atmospheric Research, Aspendale, 61
pp.
Ministry for the Environment, 2004: Preparing for Climate Change – A guide for
local government in New Zealand. Publication ME 534, Ministry for the
Environment, Wellington. 29 pp.
Mullan, B., A. Porteous, D. Wratt and M. Hollis, 2005: Changes in drought risk with
climate change. NIWA Report WLG2005-23 for Ministry for the Environment,
and Ministry of Agriculture and Fisheries, Wellington.
Climate Change and Variability – Tasman District
36
Ministry for the Environment, 2008: Climate Change Effects and Impacts Assessment.
A Guidance manual for Local Government in New Zealand. 2nd Edition. Mullan,
B., Wratt, D., Dean, S., Hollis, M., Allan, S., Williams, T., Kenny G and MfE.
Ministry for the Environment, Wellington. xviii + 149 p. Available at:
http://www.mfe.govt.nz/publications/climate/climate-change-effect-impactsassessments-may08/climate-change-effect-impacts-assessment-may08.pdf
Ramsay, D. and R. Bell., 2008: Coastal Hazards and Climate Change. A Guidance
manual for Local Government in New Zealand. Second Edition. NIWA Report for
Ministry for the Environment, Wellington. [Under preparation].
Ramsay, D. and M. Wild, 2008: Sea-level rise and climate change impacts on coastal
margins: An overview for the Tasman region. (Draft report in preparation for
Tasman District Council).
Salinger, M.J., J.A. Renwick and A.B. Mullan, 2001: Interdecadal Pacific Oscillation
and South Pacific climate. International Journal of Climatology 21, 1705-1721.
Solomon, S., D. Qin, M. Manning, R.B. Alley, T. Berntsen, N.L. Bindoff, Z. Chen, A.
Chidthaisong, J.M. Gregory, G.C. Hegerl, M. Heimann, B. Hewitson, B.J.
Hoskins, F. Joos, J. Jouzel, V. Kattsov, U. Lohmann, T. Matsuno, M. Molina, N.
Nicholls, J. Overpeck, G. Raga, V. Ramaswamy, J. Ren, M. Rusticucci, R.
Somerville, T.F. Stocker, P. Whetton, R.A. Wood and D. Wratt, 2007: Technical
Summary. In: Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental Panel
on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B.
Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press,
Cambridge, United Kingdom and New York, NY, USA.
Stroombergen, A., A. Stojanovik, D. Wratt, B. Mullan, A. Tait, R. Woods, T.
Baisden, D. Giltrap, K. Lock, J. Hendy, and S. Kerr, 2008: Costs and benefits of
climate change and adaptation to climate change in New Zealand agriculture:
What do we know so far. Ecoclimate Consortium, for Ministry of Agriculture and
Forestry. Available at: http://www.maf.govt.nz/climatechange/slm/agproduction/2008the-ecoclimate-report.pdf
Tasman District Council, 2005: Tasman Resource Management Plan (Proposed), 20
August 2005. http://www.tdc.govt.nz/pdfs/01-Introduction.pdf
Climate Change and Variability – Tasman District
37
Thompson, C.S., 2002: The High Intensity Rainfall Design System : HIRDS.
Proceedings international Conference on Flood estimation, March 2002, Berne,
Switzerland. International Commission for the Hydrology of the Rhine Basin, CHR
Report II-17, 273-282.
Willis, T.J., S.J. Handley, F.H. Chang, C.S. Law, D.J. Morrisey, A.B. Mullan, M.
Pinkerton, K.L. Rodgers, P.J.H. Sutton and A. Tait, 2007. Climate change and the
New Zealand Marine Environment. NIWA Client Report NEL2007-025 for the
Department of Conservation. 76 pp.
Wratt, D.S, B. Mullan, G. Kenny and S. Allan, 2006: New Zealand climate change:
Water and adaptation. In Chapman, R., J. Boston and M. Schwass (editors),
Confronting Climate Change: Critical Issues for New Zealand. Victoria university
Press, Wellington, pp149-162.
Climate Change and Variability – Tasman District
38
APPENDIX:
Rainfall depth-duration-frequency statistics and
scenarios.
Because the comprehensive modelling studies to identify and justify the numbers for
regionally varying changes in extreme rainfall have not yet been undertaken, the
revised Local Government Guidance Manual (Ministry for the Environment, 2008)
presently recommends use of a geographically uniform relationship between projected
changes in temperature and changes in extreme rainfall return period statistics. The
procedure outlined in the revised manual has been used in this report to derive changes
in extreme rainfall at one site in Tasman District (Richmond) for preliminary scenario
studies (“screening” studies). This method uses augmentation amounts for various
rainfall return intervals and durations set out in Table A1, which is a reproduction of
Table 5.2 of the revised Guidance Manual (Ministry for the Environment, 2008).
ARI
Table A1:
Duration
2 yrs
5 yrs
10 yrs
20 yrs
30 yrs
50 yrs
100 yrs
< 10 mins
8.0
8.0
8.0
8.0
8.0
8.0
8.0
10 minutes
8.0
8.0
8.0
8.0
8.0
8.0
8.0
30 minutes
7.2
7.4
7.6
7.8
8.0
8.0
8.0
1 hour
6.7
7.1
7.4
7.7
8.0
8.0
8.0
2 hours
6.2
6.7
7.2
7.6
8.0
8.0
8.0
6 hours
5.3
6.1
6.8
7.4
8.0
8.0
8.0
12 hours
4.8
5.8
6.5
7.3
8.0
8.0
8.0
24 hours
4.3
5.4
6.3
7.2
8.0
8.0
8.0
48 hours
3.8
5.0
6.1
7.1
7.8
8.0
8.0
72 hours
3.5
4.8
5.9
7.0
7.7
8.0
8.0
Augmentation factors (percentage increases per degree of warming) used in
deriving changes in extreme rainfall for preliminary scenario studies. [Note: In
preparing this table, all reasonable skill and care was exercised, using best
available methods and data. Nevertheless, NIWA does not accept any liability,
whether direct, indirect or consequential, arising out of its use].
Climate Change and Variability – Tasman District
39
Note that the Guidance Manual recommends that if a screening analysis using
statistics produced through this process indicates changes in heavy rainfall could lead
to problems for a particular asset or activity, then further guidance should be sought
from a science provider for a more detailed risk analysis.
This appendix first provides current rainfall depth-duration-frequency statistics for
Richmond obtained from the NIWA HIRDS V2.0 software package (Thompson,
2002), and “scenario” depth-duration-frequency tables for 2040 and 2090.
Current Statistics, Richmond: Rainfall depth-duration-frequency statistics for Richmond (Latitude
41.341S, Longitude 173.185E) from HIRDS V2.0. Numbers in the body of the table
are in millimetres
ARI
(yrs)
Duration
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
7.5
14.4
20.7
28.3
46.5
57.2
72.8
87.4
97.9
5
10.8
19.9
28.1
37.8
61.4
74.9
95.0
114.1
128.6
10
13.6
24.2
33.8
45.0
72.3
87.7
110.7
132.7
149.6
20
16.6
28.9
39.8
52.5
83.8
100.8
126.6
151.2
170.1
30
18.6
31.9
43.7
57.2
90.8
108.7
136.1
162.2
182.1
50
21.3
36.0
48.8
63.5
100.0
119.1
148.4
176.3
197.4
100
25.6
42.0
56.4
72.6
113.3
134.0
165.7
195.8
218.4
Projected future temperature changes are then used with Table A1 to provide factors
by which to multiply the entries in the current rainfall depth-duration-frequency table
for Richmond, to produce projected depth-duration-frequency tables for 2040 and
2090. The temperature changes used are the annual changes from Table 1 of the main
report, i.e.:
For 2040: Low range +0.2°C; Mid-range +0.9°C; High Range +2.0°C
For 2090: Low range +0.6°C; Mid-range +2.0°C; High Range +5.0°C
Climate Change and Variability – Tasman District
40
Richmond, 2040 Low Range (0.2°C warming)
ARI
(years
Duration
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
8
15
21
29
47
58
73
88
99
5
11
20
28
38
62
76
96
115
130
10
14
25
34
46
73
89
112
134
151
20
17
29
40
53
85
102
128
153
172
30
19
32
44
58
92
110
138
165
185
50
22
37
50
65
102
121
151
179
201
100
26
43
57
74
115
136
168
199
222
Richmond, 2040, “Mid-Range” temperature scenario (0.9°C warming)
ARI
(yrs)
Duration
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
8
15
22
30
49
60
76
90
101
5
12
21
30
40
65
79
100
119
134
10
15
26
36
48
77
93
117
140
158
20
18
31
43
56
89
107
135
161
181
30
20
34
47
61
97
117
146
174
195
50
23
39
52
68
107
128
159
189
212
100
27
45
60
78
121
144
178
210
234
Climate Change and Variability – Tasman District
41
Richmond, 2040 High Range (2.0°C warming)
ARI
(yrs)
Duration
10m
30m
60m
2h
6h
12h
24h
48h
72h
2
9
16
23
32
51
63
79
94
105
5
13
23
32
43
69
84
105
126
141
10
16
28
39
51
82
99
125
149
167
20
19
33
46
60
96
116
145
173
194
30
22
37
51
66
105
126
158
188
210
50
25
42
57
74
116
138
172
205
229
100
30
49
65
84
131
155
192
227
253
Richmond, 2090 Low Range (0.6°C warming)
ARI
(yrs)
Duration
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
8
15
22
29
48
59
75
89
100
5
11
21
29
39
64
78
98
118
132
10
14
25
35
47
75
91
115
138
155
20
17
30
42
55
87
105
132
158
177
30
19
33
46
60
95
114
143
170
190
50
22
38
51
67
105
125
156
185
207
100
27
44
59
76
119
140
174
205
229
Climate Change and Variability – Tasman District
42
Richmond, 2090, “Mid -range” temperature scenario (2.0°C warming)
ARI
(yrs)
Duration
10m
30m
60m
2h
6h
12h
24h
48h
72h
2
9
16
23
32
51
63
79
94
105
5
13
23
32
43
69
84
105
126
141
10
16
28
39
51
82
99
125
149
167
20
19
33
46
60
96
116
145
173
194
30
22
37
51
66
105
126
158
188
210
50
25
42
57
74
116
138
172
205
229
100
30
49
65
84
131
155
192
227
253
Richmond, 2090 High Range (5.0°C warming)
ARI
(yrs)
Duration
ARI
10min
30min
1h
2h
6h
12h
24h
48h
72h
2
11
20
28
37
59
71
88
104
115
5
15
27
38
50
80
97
121
143
159
10
19
33
46
61
97
116
146
173
194
20
23
40
55
72
115
138
172
205
230
30
26
45
61
80
127
152
191
225
252
50
30
50
68
89
140
167
208
247
276
100
36
59
79
102
159
188
232
274
306
Climate Change and Variability – Tasman District
43