LOCAL CLIMATE ZONES IAIN STEWART & TIM OKE. Application to heat island studies in tropical regions

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1 LOCAL CLIMATE ZONES Application to heat island studies in tropical regions IAIN STEWART & TIM OKE Department of Geography University of British Columbia Vancouver CANADA

2 LOCAL CLIMATE ZONES Stewart I, Oke T Submitted for publication.

3 LOCAL CLIMATE ZONES (LCZ) Purpose To improve method and consistency in urban heat island studies To standardize the description of city and country landscapes for urban climatologists Approach Divide landscapes into local-scale zones based on surface thermal and structural properties Test the zones for thermal climate differences using observational and numerical modeling data Application Site classification, instrument siting, heat island assessment, urban terrain and climate mapping, settlement planning, climate modeling, weather forecasting, historical temperature analysis

4 Observational support for LCZs Departure from traverse mean (K) Summary UHI datasets from Sweden (1948, 1976), Japan ( ), and Canada ( ). Observations support the divisional structure of the LCZ system. Each LCZ class has a unique thermal climate. Evening traverses in Vancouver, 2010 Temperature patterns are sensitive to surface relief, surface wetness, tree geometry, and weather. Stewart I, Oke T Preprints, 9 th Symposium on Urban Environment.

5 Numerical modeling support for LCZs Heavy industry Departure from group mean DTR (K) Departure from the group mean DTR (K) Summary S. Krayenhoff University of British Columbia Compact highrise Compact midrise Open midrise Large lowrise Highly simplified approach (trees excluded). Urban-surface (TEB) and plant-soil (CAPS) schemes coupled with atmospheric boundary layer model. Open lowrise Sparsely built Lightweight lowrise Low plants Bare soil or sand Daily temperature range (DTR) varies with building height & packing, land cover, and surface wetness. Natural zones more thermally responsive than built-up zones. See Krayenhoff et al., Preprints, 8 th Symposium on the Urban Environment.

6 LCZs and the tropical environment 1. Source areas (wind, surface geometry, boundary layer stability) HONG KONG 2. Zone combinations (mixed landscapes, ephemeral landscapes) Sao Paulo, BRAZIL Tainan, TAIWAN

7 LCZs and the tropical environment 3. Zone communication (datasheets) LCZ 1 in Kuala Lumpur: bird s eye view LCZ COMPACT HIGHRISE 1 DEFINITION Form: Dense and irregular mix of tall buildings to 10s of stories. Buildings close-set, free-standing. Sky view from street level significantly reduced. Streets paved. Buildings of steel, concrete, and glass construction. Little or no pervious ground. High space heating/cooling demand. Heavy traffic flow. Function: Commercial (office buildings, highrise hotels); residential (apartment towers). Location: City core ( downtown, central business district). Periphery (highrise subcentre, highrise sprawl). Correspondence: UCZ1 (Oke, 2004); Dc1 and Dc8 (Ellefsen, 1990/1). ILLUSTRATION High angle Eye level LCZ 1 in Hong Kong: street view PROPERTIES Sky view factor Canyon aspect ratio > Mean building height > 35 m Terrain roughness class Building surface fraction % Impervious surface fraction % Pervious surface fraction < 10 % Surface thermal admittance 1,100 1,800 J m -2 s 1/2 K ,000 1,500 2,000 2,500 Surface albedo Anthropogenic heat flux W m

8 Examples of LCZ application Barranquilla, COLOMBIA Classifying built form Nagpur, INDIA Mapping urban terrain Santiago, CHILE Assessing social inequalities Onitsha, NIGERIA Quantifying UHI magnitude Mid-latitude city Low latitude city

9 Nagpur INDIA 21 N Mapping Urban Terrain Purpose To produce an LCZ map for the city of Nagpur, and to monitor LCZ temperatures using stationary and mobile measurements. LCZ 2: Compact midrise 5 LCZ 5: Open midrise To develop a spatial database of urban form, function, and temperature distribution, and to propose a suitable use for that database in local urban planning. LCZ 9: Sparsely built LCZ 7: Lightweight lowrise Investigators R. Kotharkar, M. Surawar, VNIT (Nagpur) Kotharkar R Pers. comm.

10 Barranquilla COLOMBIA 10 N Alto Prado LCZ 1 Compact highrise San Roque LCZ 2 Compact midrise Sud Occidente LCZ 3 Compact lowrise Miramar LCZ 5 Open midrise Classifying Built Form Purpose To acquire standardized information on built form in Barranquilla, using the LCZ framework. Preliminary findings Eight different LCZs are represented in Barranquilla. Land use and land cover are highly mixed in Barranquilla; classification into LCZs requires use of zone combinations. Investigator K. Villadiego, Universidad de Paul Cézanne (Marseille) Villadiego K Pers. comm.

11 Onitsha NIGERIA 6 N LCZ 2: Compact midrise Quantifying UHI Magnitude Purpose To quantify UHI magnitude through inter-zone temperature differences (DT LCZ ). Findings LCZ 7: Lightweight lowrise Largest UHI magnitudes observed in old core (LCZ 2); smallest magnitudes in shantytown (LCZ 7). Impervious surface fractions of LCZs in Onitsha are lower than midlatitude cities; LCZ classes must be adaptable to developing cities. Investigator I.C. Nduka, Ahmadu Bello University (Onitsha) Nduka IC Research Journal of Environmental and Earth Sciences.

12 Santiago CHILE 33 S Assessing Social Inequalities Purpose To map LCZs in Santiago, observe thermal differences among LCZs, and relate these differences to socioeconomic status of district populations. Findings LCZ morphology reflects thermal and social inequalities in Santiago. High-density districts: high temperatures, high heat stress, low-income populations. Low-density districts: low temperatures, low heat stress, affluent populations. Romero H. et al Revista INVI. Investigators H. Romero et al., Universidad de Chile (Santiago)

13 FINAL REMARKS What does the LCZ system offer to tropical urban climatology? A simple user-friendly classification that does not require significant resources or sophisticated technology A flexible classification that adapts easily to hot, humid, and dry environments A standardized definition of UHI magnitude (DT LCZ ) that enables valid comparisons with midlatitude cities An educational tool for disseminating basic urban climate information A practical tool for linking urban design elements with thermal climate