Impact of Urbanization on US Surface Climate
The Role of Vegetation
Ping Zhang1,2, Lahouari Bounoua1 , Kurtis Thome1, and Robert Wolfe1
1. NASA’s Goddard Space Flight Center 2. ESSIC, University of Maryland, College Park
2015 Tree Summit Dec 18, 2015
Basics
Energy
Surface Runoff Carbon Sequestration
Background Ecology Matters
•Cities in forested areas have much larger heat islands than cities in arid areas.
•Cities in grassy or agricultural areas are somewhere in the middle
Size Matters
City: Lynchburg, VA Philadelphia, PA Pop: 7000 1563000 Size: 29 km2 (11.2mi2) 790 km2 (11.2mi2) Heat Island:5.5 C (9.9F) 11.7 C (21.1F)
Not a surprise: Bigger cities have bigger heat islands!
Development Pattern Matters
Urban area: 355 km2(137 mi2)
Tree cover at rural: 84% UHI=12 C (21.6 F) Providence
Urban area: 320 km2 (124 mi2)
Tree cover at rural: 15% UHI=7 C (12.6 F) Buffalo
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Impervious Surface Area
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Providence
Buffalo
Shape Matters
Syracuse Area:152 km2
58.7mi2 UHI: 10.6C 19 F
Harrisburg Area:152 km2
58.7 mi2 UHI: 7.6 C 13.7 F
• Use Area to Perimeter ratio (A/P ratio) to characterize the shape and the degree of cohesion of each urban area
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Impervious Surface Area
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Harrisburg
Syracuse
MODIS 1km NDVI
NLCD 30m
% impervious
Croplands
Impervious
FVC in a CMG (0.05 Deg.)
MODIS 1km LC
Fractional ndvi in a CMG (0.05 Deg.)
Combining Landsat and MODIS
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EN EB DB MF OS WS GL CL IS BS
CL
IS
WS GL
DB
MF
The Simple Biosphere model, developed in the Biospheric Sciences Laboratory code 618
Land Surface Model-SiB2
Surface laye
Root Zone
Recharge Zone
etc rc
2rb
rd
rsoil
Ec
ea
em
Ec + Eg
Eg
ra
L
Rn
P
+Wleaf
Wc
Wthro Wdrip
-Wrun
Wg
W1
W3
W2
-Wdrain
Um Tm
eci
egi
egs
z2
z1
d1
d2
d3
Canopy
Air Space
SiB2 Transfer pathway for Latent Heat
S
Water Balance
Energy Balance
Tc
Urban Heat Island
Baltimore
Washington
Surface Runoff
City DJF
Mean
JJA
Mean
Annual
Mean
Atl
anta
Precipitation 2.71 3.52 2.85
Surf
ace
runoff
Urban 1.69 62.4 1.67 47.0 1.58 55.4
MF 0.12 4.4 0.11 3.1 0.11 3.9
Was
hin
gto
n
DC
Precipitation 1.85 3.70 2.38
Su
rfac
e
run
off
Urban 0.95 51.4 1.67 45.0 1.17 49.2
BD 0.04 2.2 0.57 15.4 0.24 10.1
Carbon Lost
• About 1.4% of the current GPP is lost due to urbanization.
Trees are helpful
1. Mitigation of Heat 2. Reduction of flush floods 3. Sequestration of CO2
Thanks!
2015 Tree Summit Dec 18, 2015