METR112- Global Climate Change:Urban Climate System

Professor Menglin JinSan Jose State University

Outline:

Urban observationsUrban heat island effectUrban aerosolUrban rainfall

Through this lecture, you need to know:

Urban Heat Island EffectUrban aerosol effect on rainfallSpatial temperatures in the same region

SF, 2008

Urban Heat Island Effect (UHI): Urban surface is hotter than that of surrounding non-urban regions

Surface temperature

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/metr112-videos/MET%20112%20Video%20Library-MP4/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/metr112-videos/MET%20112%20Video%20Library-MP4/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/metr112-videos/MET%20112%20Video%20Library-MP4/urban%20system/

Animation of Atlanta Tornado

•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

Why do we need to Study Urban regions?

Related PublicationsJin, M, 2012; Development of UHI index. J. of ClimateJin, 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

% of Land Area Built-up3 - 6%

43% of Land Area Dominated by Agriculture

% of Land Area Built-up3 - 6%

43% of Land Area Dominated by Agriculture

1. Satellite remote sensing on urban regions

MODIS land coverRed color means urban built-up

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

urbanization significantly changes weather and climate

It shows that

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

Urban Heat Island Effect (UHI): Urban surface is hotter than that of surrounding non-urban regions

Surface temperature

We need to understand why and what are UHI effects

Dr. Menglin Jin San Jose State University

(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0

Urbanization Effects

Land Surface Energy Budget:

Dr. Menglin Jin San Jose State University

(1-α)Sd +LWd-εσTskin4 +SH+LE + G= 0

Urbanization Effects

Land Surface Energy Budget:

Urbanization changes:Albedo (black surface)Vegetation ocverage (EP, roughness length)Sd, LWd (by aerosols, clouds)Tskin, SH/LE/G

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/metr112-videos/MET%20112%20Video%20Library-MP4/urban%20system/

Summer Precip w-Pollution.mp4

Winter Precip w-Pollution.mp4

July 2005

NASA MODIS observed Aerosol Distribution

Urban Pollution Sources

Traffic

Industry

Indoor warming

Aerosols are solid/liquid particles pending in atmosphere

Size -0.01-100μm

Residence time – hours-days

Indirect Effect: serve as CCN

Cloud dropRain dropIce crystalIce precipitation

Aerosol Direct Effect: Scattering Absorb

0oC

surface

Black carbon heats atmosphere and surfaceMost aerosols cool surface

More aerosol ->small cloud effective radius->high cloud albedo->cooling (Kaufmann and Koren 2006)

More aerosol->reduce rainfall (Rosenfeld 2000)

Total solar radiation decreased by aerosol= 20Wm-2

(Jin, Shepherd, and King, 2005, JGR)

Aerosol decreases surface insolation

Based on NASA GMAO radiative transfer model

par AOT

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6-year averaged AERONET measurements

6-year daily averaged aerosol optical thickness (AOT) show •significant differences between Beijing and New York City•seasonal variation of urban aerosol

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New York City

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Reduction of surface insolation, Beijing

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)

Human Activities In Arid Urban Environments Can Affect Rainfall And Water Cycle

http://www.sciencedaily.com/releases/2006/06/060619222554.htm

Professor Marshall Shepherd of The University of Georgia found:

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

Turn in by March 20, 2014 to Canvas

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?

http://www.youtube.com/watch?feature=endscreen&NR=1&v=t-sXHl3l-rMWatch video:

A case for San Jose-SF Bay Area, China

3 Km5/9/2011, 8 PM

WRF 1km 5/5/20115 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

30' 117oE 30' 118oE

Understand 7/21/2012 Urban Rainfall Extremes from Space

Menglin Jin, Yu Li, Zhaohui Li, San Jose State UniversityMarshall J. Shepherd, University of Georgia

30' 117oE 30' 118oE

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1: Yan Qing2: Huai Rou3: Mi Yun4: Chang Ping5: Shun Yi6: Ping Gu7: Men Tougou8: Hai Dian9: Shi Jingshan10: Feng Tai11: Chao Yang12: Tong Zhou13: Fang Shan14: Da Xing

Beijing

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

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”

News from Media

• 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 Climate Game NamesNames

Match the city with the corresponding climatology by indicating Match the city with the corresponding climatology by indicating the appropriate letterthe appropriate letter

Sacramento, California (38°°N) _____________Phoenix, Arizona (33°N)Phoenix, Arizona (33°N) __________________________Denver, Colorado (40°N)Denver, Colorado (40°N) __________________________Iquitos, Peru (4°S)Iquitos, Peru (4°S) __________________________Mobile, Alabama (30°°N) _____________Winnipeg, Canada (50°°N) _____________Fairbanks, Alaska (65°°N) _____________