The Urban Heat Island Phenomenon

Transcription

1 The Urban Heat Island Phenomenon 1, Stefan Emeis 1 & Ulrich Reuter 2 1 Institute for Meteorology and Climate Research (IMK-IFU) of the Karlsruhe Institute of Technology (KIT), Campus Alpine, Germany 2 City of Stuttgart, Germany, Capital of the Federal State of Baden-Württemberg, Environmental Agency KIT University of the State of Baden-Wuerttemberg and National Laboratory of the Helmholtz Association

2 Overview Urban Facts Definition Driving Forces Impacts Mitigation Benefits 2

3 Some urban facts In 1900 about 3 % of the worlds population lived in cities; 33 % in the 50s and since 2007 more than 50 % of worlds population live in urban agglomerations In 2000 about 2680 cities with more than inhabitants have been counted Urban agglomerations in China increased from 20 % to 41 % (between ) Europe has an urbanization rate of 72 % 15 % of the urban population live in Mega-Cities (>10 Mill.), which are about 3 % of the total population 3

4 Urban settlements - spaces of opportunities and risks (I) Opportunities engines of global economic growth and nodal points contribute over the average to the national output Bangkok or Sao Paulo are home to about 10 15% of the national population but contribute more than 40% to the GDP provision of education and jobs is better in large agglomerations financial strength likewise opens opportunities for diversification in culture, arts and science along with technological innovation potential of cost-effective and ecologically-oriented way concentration of people potentially reduces the per-capita demand for occupied land, the cost of providing treated water or collecting solid and liquid waste 4

5 Urban settlements - spaces of opportunities and risks (II) Risks Natural risks earthquakes, floods, and landslides (75 % of the world s population lives in areas that were affected at least once by an earthquake, a tropical cyclone, floods, or drought in the last decades) Man-made (environmental and technological) risks land-use change flood risks uncontrolled waste and sewage disposal health risks Emissions, air pollution health risks Heat Island Phenomenon health risks 5

6 Urban Heat Island: Definition "Urban Heat Island" (UHI) refers to the tendency for a city or town (urbanized areas) to remain warmer than its surroundings. The annual mean temperature of a large city may be 1 2 C warmer than the surrounding areas, and on individual calm, clear nights may be up to 12 C warmer ( Heat Island Intensity). Closed isotherms indicating an area of the surface ( island) that is relatively warm; most commonly associated areas of human disturbance such as towns and cities (urbanized areas). The warmth extends vertically to form an urban heat dome in near calm, and an urban heat plume in more windy conditions. Source: Lawrence Berkeley National Lab. Source: NASA Global Hydrology and Climate Center 6

7 Types of Urban Heat Islands Boundary Layer Heat Island (BLHI) Urban Layer Heat Island (ULHI) Surface Heat Island (SHI) Source: modified after Oke (1997) 7

8 Driving Forces Weather Calm clear weather conditions / clouds reduce radiative cooling at night Geographic Location Location of a city (coastal, inland) / influence by local wind systems Time of the day and season Increasing intensity with time from sunset until the morning hours for CLHI / in high building areas also less intense / less pronounced in the BLHI / seasons change the effect City form Structure & city geometry favor heat islands / form, construction, materials and surfaces of buildings / spaces & dimension / replacement of natural surfaces City functions Heat generated from human activity / combustion / from energy usage / irrigation 8 - Public Event Meeting June 9th, 2011 Modena/Italy

9 Variations of Surface and Atmospheric Temperatures Primary Impact: Temperature Source: Environmental Protection Agency (EPA) 9

10 Intensity and Magnitude Source: Chow & Roth, 2006 Source: EPA,

11 Secondary Impacts Human Comfort Winter Summer less influence of cold seasons / increase of heat stress Energy Use Air Quality Water Use Winter Summer less energy consumption / more air conditioning Biological Activity Ice and Snow formation of urban smog / photochemical reactions higher demand of water usage / irrigation extension of the growing season less pronounced winter season Source: Sailor,

12 Heat Stress: Example Stuttgart 27 days in the city and only 6 days in the forest areas 12

13 Health Impact Source: Tan etal, 2010 Number of deaths and temperature regime in Paris during the 2003 heat wave Mortality rates in Singapore during different heat waves Source: Vandentorren et al

14 Heat Island and Climate Change Urban heat islands have some links to climate change issues but did not affect them significantly Greenhouse gas emissions from urbanized regions contribute in a high amount to global climate change Emission of particles and the interaction between particle and gas phase chemistry has the strongest link Climate modifications in urban agglomerations show similarities to projected future climate changes (cities may serve as a model for assessing the impact and for adaptation strategies on the local and global scale) 14

15 Mitigation Measures Increasing albedo reflectivity of surfaces / buildings, Increasing vegetation cover green roofs, parks, avenue trees, Decreasing runoff open water spaces, ponds, control of impervious surface areas, Decreasing anthropogenic heating air conditioning, industrial facilities,.. Increasing structural and natural shading ancient city structures 15 - Public Event Meeting June 9th, 2011 Modena/Italy

16 Benefits on meteorology reduction of temperature, wind effects, on emissions reduction of emissions, aerosols, contribution to green house emissions, on air quality reactions, photochemistry, regional influence, effective air pollution control strategy, on human health mortality, morbidity, heat stress, comfort,. on economy Source: EPA, 2009 health care system, energy consumption (e.g. 100 $ per air conditioned house),. 16

17 Thank you very much for your attention and I wish all of us a successful start of the UHI project References J.A. Voogt, Environmental Protection Agency (US-EPA); Reducing Urban Heat Islands: Compendium of Strategies, H. Taha, Meso-urban mdoelling ins upport of heat-island mitigation. IAUC Newsletter, Issue No. 39, March 2011

18 Underlying Processes 18

19 Mega Cities Tokyo (Japan) Mexico City (Mexico) New York-Newark (USA) Sao Paulo (Brazil) Mumbai (India) Dehli (India) Shanghai (China) Kolkata (India) Jakarta (Indonesia) Buenos Aires (Argentina) Dhaka (Bangladesh) Los Angeles (USA) Karachi (Pakistan) Rio de Janeiro (Brazil) Osaka-Kobe (Japan) Cairo (Egypt) Lagos (Nigeria) Beijing (China) Manila (Philippines) Moscow (Russian Federation) (UN 2001) Definition: Mega cities comprises 10 Mill. people 1975: 3 MC 2005: 20 MC 2015: 22 MC (4 > 20 Mill.)

20 MLH: General Description? Source: Stull, MLH - Public Event Meeting June 9th, 2011 Modena/Italy

21 Mixing-Layer-Height: Processes MLH / UHI Project PhD Investigations - Richard Foreman - Definitions: interaction city - surroundings 21

22 MLH: Impact & Determination needs measurements over a certain height range in-situ measurements impossible continuous observations desirable instantaneous vertical profiles Necessity for remote sensing of MLH Validation of numerical simulations (MLH as a diagnostic variable) Comparing profile (temperature, humidity, wind, TKE, air pollutants) Updating parameterisation (e.g. turbulence) Necessity for Determination of MLH 22

23 Mixing-Layer-Height: Impact 26 MLH Space for Diluation of Pollutants 23