Download Urban heat island effect, climate change, and potential adaptations

Urban Heat Island Effect, Climate Change, and Potential Adaptations in the New
York City Metropolitan Region with Case Studies on Newark, NJ and Camden, NJ
Cynthia Rosenzweig, NASA/Goddard Institute for Space Studies
William D. Solecki, Dept. of Geography, Hunter College – City Univ. of New York
Lily Parshall, Columbia University Center for Climate Systems Research
Richard Goldberg, NASA/Goddard Institute for Space Studies
Mark Chopping, Montclair State University
Prepared for presentation at the Open Meeting of the Global Environmental Change
Research Community, Montreal, Canada, 16-18 October, 2003.
Changes in local, regional, and global temperatures associated with global climate
change will both directly and indirectly impact energy transfer in cities and thus the urban
heat island effect. It is possible that a synergistic relationship will develop between the
urban heat island effect and global climate change in the 21st Century.
In the New York Metropolitan Area, analysis of National Climatic Data Center
data at 23 weather stations revealed a warming trend of 0.109°C per decade. This
corresponds to a total warming of approximately 1.0°C over the 20th Century. During the
first quarter of the 20th Century, an urban heat island of at least 1.0°C is apparent in the
data (Sastre, 2003). Based on mesoscale work done by Gedzelman et al., the magnitude
of the heat island effect averaged about 4°C in the summer and autumn and 3°C in the
winter and spring during 1997 – 1998 (Gedzelman et al., 2003).
The magnitude of the urban heat island effect varies both spatially and
temporally. In general, the heat island effect is maximized on clear days, when incoming
solar radiation is high and nighttime cooling proceeds most slowly. In the Newark area,
Landsat Thematic Mapper 5 images acquired for June 2, 1996 showed that surface
temperatures in Newark were on average 5.9°C higher than surface temperatures in
surrounding areas and that surface albedo plays a significant role in urban-suburban
surface heating differences (Figure 1). In the Camden area, Landsat Thematic Mapper 7
images acquired for September 23, 1999 and August 14, 1999 showed that surface
temperatures could be correlated to land-use, with the hottest temperatures recorded for
urban areas and barren land and the coolest temperatures recorded for water and
wetlands. Further analysis showed that as population density decreases, average surface
temperature decreases.
Under favorable meteorological conditions including high solar radiation, low
windspeed and low cloud cover, elevated surface temperatures translate into elevated air
temperatures. Analysis of weather station data for Newark, NJ and Camden, NJ for the
period 1950 – 1999 showed an urban-suburban mean temperature difference of 1.6°C for
the Newark region and 0.7°C for the Camden region. The difference in urban-suburban
minimum temperature, taken as the magnitude of the urban heat island effect, was
significantly greater: 3.0°C for Newark and 2.2°C for Camden.1
For Newark, a peak in urban heat island magnitude was seen in October; for
Camden, the peak was seen in August.
Most of the variability in urban-suburban
temperature differences was explained by monthly variations in windspeed and cloud
cover. In agreement with previous studies, lower-than average windspeeds and lowerthan average cloud cover resulted in above average urban heat island intensity for both
Newark and Camden (Figure 2). Preliminary analysis of global climate model (GCM)
and regional climate model (RCM) output showed that while cloud covers are expected
to slightly increase, windspeeds are expected to slightly decrease in the 21st Century
(Figures 3a & 3b). The urban heat island may not be further enhanced due to the balance
between decreased windspeed and increased cloud cover.
However, current trends scenarios as well as GCMs project significant increases
in regional temperatures over the 21st Century (Figure 4). Downscaling the GISS GCM
using the Mesoscale Model 5 (MM5) developed by the National Corporation for
Atmospheric Research projects a warming of up to 2.5°C for the 2050s in New Jersey.
Warming temperatures in the highly urbanized New York Metropolitan Region
are likely to amplify current energy, air quality, and health problems. The spatial area
over which “urban-heat-island-like” conditions are felt is likely to expand and the adverse
impacts of the interactions between the urban heat island effect and local air pollution are
likely to be felt with greater frequency and intensity.
1
For both the Newark and Camden analyses, the absence of a working weather station within the city
proper required using the nearest airport station as a proxy. In the case of Newark, the Newark
International Airport located on the southern edge of the city was used. In the case of Camden, the
Philadelphia airport was used.
2
References
Gedzelman, S.D., S. Austin, R. Cermak, N. Stefano, S. Partridge, S. Quesenberry, and
D.A. Robinson (2003) Mesoscale aspects of the Urban Heat Island around New York
City. Theoretical and Applied Climatology. 75 (1-2), 29-42.
Sastre, M.P. (2003) The History of the Urban Heat Island Effect in New York City.
Master’s Thesis. Columbia University Faculty of Architecture and Planning.
Figure 1. Thermal map of summer (June 2, 1996) surface temperatures. White areas
represent hottest surface temperatures. Black areas, for the most part, represent areas
covered by clouds. Regions 1-2: suburban; 3-4: low-rise urban; 5-6: medium-rise
urban; 7: high-rise urban. Regions 3-6 are within the city of Newark.
3
80
5.0
70
4.0
60
3.0
50
2.0
40
1
2
3
4
5
6
7
8
9
10
11
Sky cover (%)
Temperature difference (deg C) and wind
speed (m/s)
6.0
12
Month
Temperature differences
Wind speed
Daytime sky cover
Night-time sky cover
Figure 2. Urban-suburban temperature differences, windspeed, and sky cover for Newark,
NJ area. Monthly averages for the period 1984 - 1995
Wind Speed Change (%)
Cloud Cover Change (%)
10
10
5
5
0
0
-5
-5
2020s
2050s
GSA2
2080s
2020s
GSB2
Figure 3a. GISS GCM estimations of potential windspeed
changes for three scenarios for Newark, NJ area.
2050s
GSA2 GSB2
2080s
Figure 3b. GISS GCM estimations of potential cloud
cover changes for three scenarios for Newark, NJ area.
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20.0
19.0
18.0
17.0
°C
16.0
15.0
14.0
13.0
12.0
11.0
10.0
1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080
Year
Temp C
calculated T
GSGG
GSGS
CCGG
CCGS
HCGG
HCGS
Figure 4. Currents trends and projected temperature change scenarios for Camden, NJ area. Calculated T shows the current
trends scenario. GSGG shows the GISS GCM scenario with greenhouse gas forcing and GSGS shows the GISS GCM
scenario with greenhouse gas plus sulfate aerosol forcing (GSGS). GISS GCM simulations use observed greenhouse gases
until 1990 and compounded 0.5% increases in CO2 thereafter. CCGG and CCGS scenarios were generated using the
Canadian Center GCM. HCGG and HCGS scenarios were generated using the Hadley Center model.
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