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
Mechanisms for UHI
• 1. Dark surface leads to more solar radiation
absorbed at the surface and thus increases surface
temperature
• 2. Vegetation cover is reduced and thus
evaporation is reduced
• 3. Water proof urban surface has no soil moisture,
leading to more heat to warm up the surface
• 4. Building walls extend the effective urban
surfaces
Video: Urban Rainfall Effect
http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/urban%20system /
Urban Rainfall Effect.mp4
Mechanisms for urban effects on
rainfall
• 1. UHI leads to stronger convection and
thus clouds formation and rainfall
• 2. Buildings lift air to form clouds and thus
rainfall
• Air pollution serve as CCN to form clouds
and rainfall
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
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
Urban Heat Island Effect (UHI)
Is it a
• day time phenomenon only
• night time phenomenon only
• both day+night phenomenon
How to deal with UHI?
Watch video:
http://www.youtube.com/watch?feature=endscreen&NR=1&v=t-sXHl3l-rM
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
Urban Extreme Weather
• Flood
• Heat wave
• coldwave
• 2003 European heat wave
– One of the deadliest heat waves in European
history.
– Many regions were as much as 18 degrees F
above average!!!
– Affected Western and Central Europe.
– Over 40,000 Europeans died!!!!
– Similar event in Russia, 2010
• The Shutdown of the Thermohaline
Conveyor would cause abrupt cooling,
especially in Europe.
• This change could occur in as little as ten
years after the shutdown (not a few days
like The Day After Tomorrow)
• Suddenly, many northern countries would
almost become uninhabitable.
– Major political implications
– Wars
Understand 7/21/2012 Urban Rainfall Extremes
from Space
Menglin Jin, Yu Li, Zhaohui Li, San Jose State University
Marshall J. Shepherd, University of Georgia
42oN
30'
41oN
30'
40oN
30'
39oN o
115 E
30'
116oE
30'
117oE
30'
118oE
Beijing
42oN
1: Yan Qing
2: Huai Rou
3: Mi Yun
4: Chang Ping
5: Shun Yi
6: Ping Gu
7: Men Tougou
8: Hai Dian
9: Shi Jingshan
10: Feng Tai
11: Chao Yang
12: Tong Zhou
13: Fang Shan
14: Da Xing
30'
41oN
2
1
30'
3
4
5
o
7
40 N
6
8
11
9
10
12
13
14
30'
39oN o
115 E
30'
116oE
30'
117oE
30'
118oE
July 21, 2012, Beijing
• the heaviest rainfall in 61 years fell on the
Chinese capital city of Beijing on July 21,
2012. The state news agency Xinhua at first
said that 37 people had been killed by
floods during and after the downpour, but
today (July 26, 2012) the official death toll
was raised to 77
• Extreme to 200mm
• Affect 1.9million people, 10 billons $
damage
News from Media
从10时开始的强降雨给北京造成不小的困扰，多个区县的降雨量超过历史极值，房山河北
镇的降雨甚至达到了460毫米。截至目前，降雨共造成10人死亡，数条路段被淹，仍未通行。
昨天10时开始，从北京西南地区开始，自西向东出现强降雨。截至今天06时，北京大
部地区出现大暴雨，部分地区出现特大暴雨。监测显示，昨天10时至今天06时，全市平均
雨量为170毫米，城区平均为215毫米，模式口为328毫米，西南平均为213毫米，最大降雨
出现在房山河北镇，降雨量达到460毫米；最强降雨出现在平谷挂甲峪，昨天20时至21时一
小时降雨量达到100.3毫米。
今天早上8时左右，降雨过程已经基本结束。北京市气象局首席预报员郭金兰介绍：
“此次降水过程雨量大、降水急、范围广。从监测资料分析来看，海淀、密云、门头沟、
房山等多个站点测得的降雨量，均为这些监测站建站以来的最大值。”
“这场降雨威力如此之大，有水汽、地形、热岛效应三个主要原因。持续几天的闷热
给京城积蓄了充沛的水汽，昨天北京以南的水汽又源源不断地输入，将空气湿度送至饱和。
而城市热岛效应，使城区气温难以回落，水汽无法流失。北京西部、北部环山的特殊地形，
则使被堵截的气流更加勤奋地做抬升运动。这种情形下，一遇到冷空气活动，对流云团就
即刻得到强烈发展。”北京市气象台专家乔林分析道，“冷暖空气的交汇点恰好处于北京
上空，因此持续时间长，雨强较大，还伴有雷电。”
“The rainfall extreme is due to water vapor, geographic,
and urban heat island effect”
• 全市平均降雨量170毫米，城区平均降雨
量225毫米，为新中国成立以来北京市最
大的一次降雨过程，降雨量在100毫米以
上的面积占全市的86%以上；降 雨历时
之长历史罕见，强降雨一直持续近16个
小时；局部雨强之大历史罕见，全市最
大降雨点房山区河北镇为 460毫米，接近
500年一遇；局部洪水之巨历史罕见，拒
马河最大流量达每秒2500立方米，北运
河最大流量达每秒1700立方米。
“…Continuously pour 16 hours…”
A car moves on the rain-inundated road
in the Daxing District of Beijing, capital of China, July 21, 2012.
Mechanisms for extreme rainfall
over BJ: Why Beijing?
Urban landscape enhance rainfall via three
processes:
• Aerosol-cloud interactions
• UHI
• Canyon effect
Identified from satellite remote sensing
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)
_____________
_____________
_____________
_____________
_____________
_____________
_____________