Urbanization and Climate Change in South China

Johnny ChanGuy Carpenter Asia-Pacific Climate Impact Centre

School of Energy and Environment

City University of Hong Kong

1Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Outline

Background

Effects of urbanization

Evidence

Summary

2Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Urban Area

Hong Kong

Shenzhen

Guangzhou

Farmland in Guangdong

vs. Farmland

3Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Urban or

Built-up (km2) :

Year : 1980

2230

Urban or Built-up Area in the Pearl River Delta

1980

1990

3950

1990

2000

6570

2000

4Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Effects of Urbanization on Climate

Urbanization

Emission of

atmospheric

pollutants

Changes in

land use

Heat Island

Effect/Land-

sea BreezeChanges in runoff patterns

and momentum fluxes

Changes in

cloud

condensation

nuclei

concentration

Changes in

cloud

amounts

and hence

rainfall

Changes in

radiation

budget

Changes in heat and

moisture fluxes

5Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Cloud and Rain Formation

6Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Clean vs. Polluted Clouds

7Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Heat Island Effect

8Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Land-sea Breeze Circulation

9Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Land Use Changes

1979

2003

10Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Simulated Flow in a densely built area

11Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Simulated Vertical Wind Profile

12Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Simulated Flow pattern at 5 m

13Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

evaporation

heat

exchangemomentum

exchange

LAND

ATMOSPHERE

absorption of

rain water

Land-Atmosphere Exchanges

reduced due to

increase in paved

land vs. soil

increased due

to heat island

effect

reduced due

to large

number of

buildings,

especially tall

ones

14Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

HK temperature

HK solar radiation

No. of haze

days in

Guangzhou

Climate Change

in the PRD

(related to

radiation)

15Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Climate Change

and Urbanization

in the PRD

(related to water)

PRD relative humidity

PRD rainfall

16Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Effect of increasing the roughness of the Earth’s surface on rainfall

17Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Effect of turning off the moisture flux on rainfall

18Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong

Summary

Urbanization causes substantial changes in the energy balance of the region

Such changes in energy balance will cause changes in wind flow patterns, not only within the region but also those areas downstream of the urbanized region.

A comprehensive study of the effects of urbanization on regional climate needs to be carried out to quantify such effects.

How such effects may be modified under global warming also needs to be ascertained.