Remote Sensing of the Urban Heat Island Effect Across...
Transcript of Remote Sensing of the Urban Heat Island Effect Across...
Remote Sensing of the Urban Heat
Island Effect Across Biomes in the
Continental USA
Marc Imhoff , Lahouari Bounoua, Ping Zhang, and Robert Wolfe
NASA’s Goddard Space Flight Center
Land Cover Land Use Change - 2012
Studying the UHI Phenomenon
Focus on surface temperature
- influenced by albedo, emissivity, and surface fluxes.
Bioclimatic context
- setting is important as UHI is a relative measure
(Temp of urban core compared to nearby non-
urban cover).
- Important to climate change as urbanization of
specific biomes represents a departure from
previous flux characteristics.
- Impact may be disproportionate to simple area
based assessments. 2
Urban Occupation of Fertile Soils
0
1
2
3
4
5
6
7
8
0 1 2 3 4 5 6 7 8
Percent of Soils (UN/FAO) Covered by LightsGrouped by Number of FCC Limiting Factors
Per
cent
of S
oil A
rea
Cov
ered
by
Ligh
ts
Number of Factors Limiting Agriculture
CHINA
Consequences of Urbanization
NPP Lost or Gained (annually) going from a
pre-urban to a post urban world
Annual loss of food web energy 400 Trillion kilocalories
(roughly equal to food energy requirement for 448 million people).
Reduction of actual food products for 16.5 million persons annually.
Disproportionate impact: Urbanization (3% surface area) has reduced
Continental NPP by 41.5 Million tons C/year
Roughly equal to the gains made by agriculture (40% surface area).
Imhoff et al. 2004, RSE, Vol. 89, Issue 4, pp. 434-443.
Consequences of
Urbanization on NPP
DMSP/OLS Urban Map
Urban, Peri-urban, Non-urban
AVHRR Monthly NPP (g Cm-2)
NPP and Local Climate: Urban Heating Extends
Satellite Observations
Winter NPP
gain negated
in peak
season by
reduced
vegetation
and heat
stress.
Seasonal Offset
diminishes in
tropics
Length of growing season
locally in cold climates.
In semi-arid regions cities
enhance NPP relative to
surrounding areas
North East
Mid-Atlantic
South East South West
Atlanta Urban Heat Island and Air Quality Modeling Study
D. Quattrochi, MSFC
120oF 49oC
Surface Temperature and Albedo
83oF 28oC
7
Surface composition (parameters)
in and outside urban area
8
Schematic functioning of the Simple Biosphere Model (SiB2)
showing the pathway for the latent heat flux calculation.
Surface Layer
Root Zone
Recharge Zone
etc r c
2r b
r d
r soil
l E c
e a
e m
l E c + l E g
l E g
r a
S L
R n
P
+W leaf
W c
+ W thru W drip
-W run W g
W 1
W 3
W 2
-W drain
U m
T m
eci
T c
egi
egs
z 2
z 1
d 1
d 2
d 3
Canopy
Air Space
SiB2 Transfer pathway for Latent Heat Radiation
Precipitation
Interception Loss
interception
Ground evaporation
Transpiration
More than Albedo Biome Level Surface Parameters Influence Heat
9
Datasets and compilations
Domains: cities in U.S.
Scales: cities with area size from 10km2 to more than 4000 km2
Datasets:
- Impervious surface area (ISA) from the Landsat TM-based NLCD 2001 dataset [Yang et al., 2002 ]
- Land surface temperature (LST) from MODIS [Wan et al., 2004]
- Terrestrial ecoregion map developed by Olson et al [2001]
- Topographic data from SRTM30 [Farr and Kobrick, 2000]
- NDVI from MODIS [Huete et al., 1997]
10
Geospatial urban area definition using Landsat
Impervious Surface Area
Identifies boundary between urban and low intensity residential area
Provide spatially coherent urban groups
11
Classification of urban density
12
Classification of urban density
Four broad biomes: forest, grass/shrub, arid (desert and
xeric shrubland), and semi-arid (Mediterranean)
323 settlements are evenly distributed over USA ranging
from around 10 km2 to more than 4,000 km2
Five urban zones are defined based on ISA density
- Urban core pixels: 75% > ISA ≥ 50%
- Medium density urban pixels: 50% > ISA ≥ 25%
- Suburban pixels: 0 to 5 km outside the 25% ISA contour
- Rural pixels: 15 to 20 km outside the 25% ISA contour
Sampling is constrained by biome and elevation
UHI=LSTurban core- LSTRural
13
UHI and ecological context
Average UHI for US cities grouped by biomes
-2
0
2
4
6
8
Forest Grass Mediterranean Desert
UH
I (d
egre
e)
• UHI=7.1 oC in cities built in forest
• UHI=4.2 oC in cities built in grass/shrubs
• UHI=6.0 oC in cities built in Mediterranean
• UHI=0.25 oC in cities built in desert
• The average city size of each group is 159/206/1055/160 km2
14
UHI Baltimore vs. Las Vegas
• Baltimore, Maryland, in Notheastern temperate broadleaf and mixed forest
• Las Vegas, Nevada, in desert and xeric shurbland
Baltimore Las Vegas
0
20
40
60
80
Avera
ge I
SA
(%
)
Urban Core (ISA>=75%)
Urban1 (75%>ISA>=50%)
Urban2 (50%>ISA>=25%)
Suburban (0-5Km buffer)
Rural (45-50Km buffer)
A
Baltimore Las Vegas
0.0
0.2
0.4
0.6
0.8
B
Jun-Aug LST
Jun-Aug NDVI
Avera
ge N
DV
I
Fractional ISA
Baltimore Las Vegas
25
30
35
40
45
50
55
C
Avera
ge L
ST
(C
)
15
UHI and ecological context: Baltimore vs. Las Vegas
Composite averaged LST during summer (Jun-Jul-Aug) day time
across all urban zones at Baltimore and Las Vegas.
25
30
35
40
45
50
55
60
Las Vegas
Baltimore
Avera
ge s
um
mer
daytim
e L
ST
(C)
50km 20km 15km 10km 5km 25% core 25% 5km 10km 15km 20km 50km
The composite summer daytime LST profile
25
30
35
40
45
50
55
60
A Biome-Centric View of Remotely Sensed Surface Parameters in US cities
Imhoff, Zhang, Wolfe and Bounoua, 2009, RSE 114 (2010)
Urban Heat Islands and Ecological Context
MODIS - Aqua LST (2003-2005)
Summer = Jun-Aug (average LST)
Winter = Dec - Feb (average LST) LST at 1:30 pm local time
Day = 1:30PM Local time
Night = 1:30AM Local time
Imhoff, Zhang, Wolfe and Bounoua, 2009, RSE 114 (2010)
FE FA GN DE MS GS GT
FW
18
Quantifying the relationship between LST and ISA
Variations in ISA explain 88% of the variation in LST for urban areas in forested biomes
The rate of change in LST as a function of ISA is 11.5% for urban areas in forests, while only 6.9% for those characterized by short vegetations.
In desert environments, the LST’s response to ISA presents is a “U-shaped” horizontal gradient decreasing from the urban core to the outskirts of the city and then increasing again in the suburban to the rural zones
A: Cities in forests
LST = 0.115 X ISA
R2 = 0.88
-8
-6
-4
-2
0
2
4
6
8
-40 -20 0 20 40
NLCD2001 ISA anomaly (%)
Su
mm
er
da
y L
ST
an
om
aly
(oC
) B: Cities in desert
LST = 0.001 X ISA2 + 0.010 X ISA - 0.54
R2 = 0.14
-8
-6
-4
-2
0
2
4
6
8
-40 -20 0 20 40
NLCD2001 ISA anomaly (%)
Su
mm
er
da
y L
ST
an
om
aly
(oC
)
19
The magnitude of UHI and size of urban area
Average UHI for US cities grouped by size
0
2
4
6
8
10
10-100 100-1000 >1000 (km2)
UH
I (d
eg
ree)
Forest Grass
• US urban settlements are grouped based on the total contiguous area for
each urban polygon defined by 25% ISA threshold
• Average UHI during summer day time is affected by urban size
20
UHI and urban extent for discrete urban
centers in temperate forest (continental US)
Urban extent defined by contiguous area with 25%+ ISA
21
Conclusions and future directions
This research highlights significant positive relationships
between the UHI magnitude, the ISA, and ecological setting
estimated exclusively from remotely sensed observations
The use of ISA as an estimator of the extent and intensity of
urbanization is more objective than population density based
methods and can be consistently applied across large areas for
inter-comparison of impacts on biophysical processes.
We will use a combination of satellite and ecological map data
to extend the characterization of the UHI response to global
urban settlements.
The uncertainties in ISA outside USA are challenges for future
studies as the concept of ISA in the USA does not necessarily
transfer to many developing country cities where infrastructure
characteristics and properties are often different