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

Urban Heat Island.mp4

reasons for UHI how to reduce UHI

Video: Urban Rainfall Effect

http://www.met.sjsu.edu/metr112 videos/MET%20112%20Video%20Library MP4/urban%20system /

Urban Rainfall Effect.mp4

Video

• Observe urban system effect

http://www.met.sjsu.edu/metr112 videos/MET%20112%20Video%20Library MP4/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 Red color means urban built-up 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)S

d

+LW

d

-εσT

skin 4

+SH+LE + G= 0

Dr. Menglin Jin San Jose State University

Urbanization Effects Land Surface Energy Budget:

(1-α)S

d

+LW

d

-εσT

skin 4

+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 ) Urban reduces surface emissivity -> Less longwave radiation emitted from surface  More heat is kept at surface  Surface temperature increases (Jin et al. 2005, J. of Climate)

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

NASA MODIS observed Aerosol Distribution

July 2005

Urban Pollution Sources Traffic Aerosols are solid/liquid particles pending in atmosphere Size -0.01-100μm Residence time – hours-days Industry Indoor warming

Aerosol Direct Effect: Scattering Absorb Indirect Effect: serve as CCN 0 o C

surface Cloud drop Rain drop Ice crystal Ice precipitation Black carbon heats atmosphere and surface Most aerosols cool surface 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

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0 1 2 5 6 7 Beijing Beijing New York New York City 3

month

4 6-year daily averaged aerosol optical thickness (AOT) show •significant differences between Beijing and New York City •seasonal variation of urban aerosol

0 0 -20 -120 -140 -160 -40 -60 -80 -100 Reduction of surface insolation, Beijing

Beijing Ftotal

1 2 3 4 5 6 7

month

6am/6pm 7am/5pm 8am/4pm 9am/3pm 10am/2pm 11am/1pm 12pm

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 Turn in by October 10, 2012 to D2L

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) _____________ _____________ _____________ _____________ _____________ _____________ _____________