METR112- Global Climate Change:
Urban Climate System
Professor Menglin Jin
San Jose State University
Outline:
Urban observations
Urban heat island effect
Urban aerosol
Urban rainfall
Through this lecture, you need to know:
Urban Heat Island Effect
Urban aerosol effect on rainfall
Spatial temperatures in the same region
SF, 2008
Surface temperature
Urban Heat Island Effect (UHI):
Urban surface is hotter than that of surrounding non-urban regions
We need to understand why and what are UHI effects
Review: how surface Temperature is measured
Video: Urban Heat Island Effect
(UHI)
http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/urban%20system/
Urban Heat Island.mp4
reasons for UHI
how to reduce UHI
Video: Urban Rainfall Effect
http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/urban%20system /
Urban Rainfall Effect.mp4
Video
• Observe urban system effect
http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/urban%20system/
Animation of Atlanta Tornado
Why do we need to Study Urban regions?
•Urban is an extreme case of human-change natural land cover.
•Urban regions has strong pollution, greenhouse emission.
•60% people in USA live in cities
•Urban has unique water and heat cycles what directly
affect human life
Related Publications
Jin, M, 2012; Development of UHI index. J. of Climate
Jin, M., J. M. Shepherd, M. D. King, 2005: Urban aerosols and their
interaction with clouds and rainfall: A case study for New York and Houston.
J. Geophysical Research, 110, D10S20,
doi:10.1029/2004JD005081.
Jin, M, R. E. Dickinson, and D-L. Zhang, 2005:
The footprint of urban areas on global climate as characterized by
MODIS. Journal of Climate, vol. 18, No. 10, pages 1551-1565
Jin, M. and J. M. Shepherd, 2005: On including urban landscape in land surface
model – How can satellite data help? Bull. AMS, vol 86, No. 5, 681-689.
Jin, M. J. M. Shepherd, and Christa Peters-Lidard, 2007: Development of A
Parameterization For Simulating the Urban Temperature Hazard Using
Satellite Observations In Climate Model in press by Natural Hazards.
Jin, M. and M. J. Shepherd, 2007: Aerosol effects on clouds and rainfall: urban vs.
ocean. Revised for JGR
43% of Land Area
Dominated by Agriculture
% of Land Area
Built-up
3 - 6%
43% of Land Area
Dominated by Agriculture
% of Land Area
Built-up
3 - 6%
1. Satellite remote sensing on urban regions
MODIS land cover
Night Light of Tokyo
Night Light of Paris
pictures made by U.S. Defense Meteorological Satellites Program (DMSP)
Satellite observations retrieve urban system:
Land surface properties:
surface temperature, surface albedo, emissivity, soil moisture, vegetation cover
Atmosphere conditions: aerosol,
clouds, and rainfall
It shows that
urbanization significantly
changes weather and climate
Urban Heat Island Effect (UHI)
This phenomenon describes urban and suburban temperatures
that are 2 to 10°F (1 to 6°C) hotter than nearby rural areas.
UHI impacts:
Elevated temperatures can impact communities by increasing
peak energy demand, air conditioning costs, air pollution levels,
and heat-related illness and mortality
High temperature also enhances surface convection,
and causes more clouds and rainfall
Surface temperature
Urban Heat Island Effect (UHI):
Urban surface is hotter than that of surrounding non-urban regions
We need to understand why and what are UHI effects
Urbanization Effects
Land Surface Energy Budget:
(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0
Dr. Menglin Jin
San Jose State University
Urbanization Effects
Land Surface Energy Budget:
(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0
Urbanization changes:
Albedo (black surface)
Vegetation ocverage (EP, roughness length)
Sd, LWd (by aerosols, clouds)
Tskin,
SH/LE/G
Dr. Menglin Jin
San Jose State University
Urbanization impacts on skin temperature
10°C !!!
EOS MODIS observed monthly mean daytime shows evident urban heat island effect
(Copied from Jin et al, 2005a). The red areas show the dense building regions of Beijing.
Urbanization changes surface albedo (MODIS)
Urban surface albedo has a 4-6% decrease ->
more solar radiation will be absorbed at surface\
increase surface temperature
Urbanization reduces surface emissivity (MODIS)
(Jin et al. 2005, J. of Climate)
Urban reduces surface emissivity ->
Less longwave radiation emitted from surface 
More heat is kept at surface
Surface temperature increases
What Can be Done ?
to reduce negative Urban heat island effects?
Education : a key component of many heat island reduction effort
Cool Roofs: Over 90% of the roofs in the United States are dark-colored.
These low-reflectance surfaces reach temperatures of 150 to 190°F (66 to 88°C)
Trees and Vegetation
Cool Pavements
Cool Roofs
Cool roof systems with high reflectance and emittance
stay up to 70°F (39°C) cooler than traditional materials
during peak summer weather.
The Utah Olympic Oval uses cool roof technology.
What Is a "Cool Roof"?
Cool roof materials have two important
surface properties:
•a high solar reflectance – or albedo
•a high thermal emittance
Solar reflectance is the percentage of solar energy
that is reflected by a surface. Thermal emittance is defined
as the percentage of energy a material can radiate away after
it is absorbed.
3. Urban Aerosols and Their Direct Effects on
Clouds, Surface Insolation, and Surface Temperature
Video
• Urban aerosol effect on rainfall
http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/urban%20system/
Summer Precip w-Pollution.mp4
Winter Precip w-Pollution.mp4
NASA MODIS observed Aerosol Distribution
July 2005
Urban Pollution Sources
Traffic
Aerosols are solid/liquid particles
pending in atmosphere
Size -0.01-100μm
Industry
Indoor
warming
Residence time – hours-days
Aerosol Direct Effect: Scattering
Indirect Effect: serve as CCN
Absorb
0o C
surface
Black carbon heats atmosphere and surface
Most aerosols cool surface
Cloud drop
Rain drop
Ice crystal
Ice precipitation
More aerosol ->small cloud effective radius->
high cloud albedo->cooling (Kaufmann and Koren 2006)
More aerosol->reduce rainfall (Rosenfeld 2000)
Aerosol decreases surface insolation
Total solar radiation decreased by aerosol= 20Wm-2
Based on NASA GMAO radiative transfer model
(Jin, Shepherd, and King, 2005, JGR)
6-year averaged AERONET measurements
par AOT
0.9
0.8
Beijing
0.7
0.6
0.5
Beijing
New York
0.4
0.3
New York City
0.2
0.1
0
0
1
2
3
4
5
6
7
month
6-year daily averaged aerosol optical thickness (AOT) show
•significant differences between Beijing and New York City
•seasonal variation of urban aerosol
Reduction of surface insolation, Beijing
Beijing Ftotal
0
0
1
2
4
3
5
6
7
-20
-40
change in flux
-60
6am/6pm
7am/5pm
8am/4pm
-80
9am/3pm
10am/2pm
11am/1pm
12pm
-100
-120
-140
-160
month
Urban Effects on Climate: An Analogue
Urban Effects on Radiative Forcing Known, but Effects on
Water Cycle Processes (e.g. Precipitation Variability) Less
Understood (IPCC, 2007)
Professor Marshall Shepherd of The University of Georgia found:
Human Activities In Arid Urban Environments
Can Affect Rainfall And Water Cycle
http://www.sciencedaily.com/releases/2006/06/060619222554.htm
a 12-14 percent increase (which scientists call an anomaly)
in rainfall in the northeast suburbs of Phoenix from
the pre-urban (1895-1949) to post-urban (1950-2003) periods.
Extra Credit Activity (1)
(a): Read this link and (b) write a 1-page summary
A case for San Jose-SF Bay Area, China
5/9/2011, 8 PM 3 Km
WRF 1km 5/5/2011
5 PM
6 PM, 5/5/2011
7 PM, 5/5/2011
5 PM, 5/6/2011
7 PM, 5/6/2011
9 PM, 5/6/2011
11 PM, 5/6/2011
1 AM, 5/7/2011
3 AM, 5/7/2011
5 AM, 5/7/2011
8 AM, 5/7/2011
10 AM, 5/7/2011
Class participation:
Climate Game!
City A
City B
City C
City D
City E
City F
City G
Climate Game
Names
Match the city with the corresponding climatology by indicating
the appropriate letter
Sacramento, California (38°N)
Phoenix, Arizona (33°N)
Denver, Colorado (40°N)
Iquitos, Peru (4°S)
Mobile, Alabama (30°N)
Winnipeg, Canada (50°N)
Fairbanks, Alaska (65°N)
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