Landscape Representation and the Rural - Urban Divide in Urban Heat Island Literature Iain Stewart and Tim Oke

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1 Landscape Representation and the Rural - Urban Divide in Urban Heat Island Literature Iain Stewart and Tim Oke Department of Geography University of British Columbia Vancouver, Canada

2 Outline Defining the urban heat island (UHI) Problems and concerns with urban and rural station designations Suggestions and possible solutions for re-defining UHI intensity 2

3 Defining the Urban Heat Island UHI OBSERVATION (Oke 1995) AIR SURFACE SUB- SURFACE UBL UCL GROUND DATA COLLECTION REMOTE DATA COLLECTION MOBILE SENSOR FIXED SENSOR UHI = Tu - Tr STATIONARY UNITS URBAN CANOPY LAYER (Oke 1976) 'URBAN' 'RURAL' 'URBAN' 'RURAL' 0km1km2km (Stewart 2000) 3

4 Problems with Urban-Rural Station Designations Background Urban and rural stations provide a simple and conventional method for measuring UHI magnitude Climate literature is overwhelmed with empirical UHI studies, dating from Luke Howard s (1833) temperature observations in London Problem Defining stations as urban and rural is NOT intuitively clear Standardized and universally recognized measures of UHI intensity have not been established Inter-city comparisons and generalizations of UHI are problematic 4

5 Problems with Urban-Rural Station Designations Specific Concerns Urban and rural are subjective terms that are open to variable interpretation Selection of urban/rural sites may be influenced by personal or cultural biases 'URBAN' 'RURAL' 0km1km2km Describing stations as urban and rural does not convey the local and microscale exposure characteristics of those sites 5

6 Problems with Urban-Rural Station Designations Sites representing T(urban) and T(rural) in UHI literature URBAN RURAL URBAN AND RURAL street canyons agriculture academies airports building rooftops plantations schools housing estates paddy fields universities railyards, shipyards potato fields meteorology institutes hospitals, parking lots wheat fields weather observatories golf courses fruit farms botanical gardens city parks villages We aim to measure the same phenomenon (i.e., UHI intensity), but our means of achieving that aim are scattered across different surfaces types and exposures 6

7 Problems with Urban-Rural Station Designations URBAN SITES RURAL SITES Goteborg SWEDEN (Eliasson, 1994) Uppsala SWEDEN (Taesler, 1981) HONG KONG (Giridharan et al., 2005) Wroclaw POLAND (Szymanowski, 2005) 7

8 Problems with Urban-Rural Station Designations?????? Phoenix USA Vienna AUSTRIA Szeged HUNGARY Vancouver CANADA 8

9 Problems with Urban-Rural Station Designations Specific Concerns Urban rural divide is an outdated and overly simplistic concept for universal landscape classification Regina: city-based urbanism Guangzhou: region-based urbanism Complex landscapes surrounding large cities are difficult to describe as either urban o rural; in fact, they are neither urban no rural 9

10 Suggestions and Possible Solutions for Re-defining UHI Magnitude Problem Summary Urban-rural station designations are inconsistent, ambiguous, and misleading Urban climatology lacks a comparative framework for defining and observing UHI intensity in the canopy layer 10

11 Suggestions and Possible Solutions for Re-defining UHI Magnitude Suggestion Provision of metadata (Oke 2004; Peterson 2003) Classifying stations only as urban or rural is not good enough! We need detailed information about micro- and localscale site character sky view, surface cover and roughness, soil moisture, artificial heat, physical terrain But metadata alone don t constitute a framework 11

12 Suggestions and Possible Solutions for Re-defining UHI Magnitude Possible Solution A new landscape classification scheme that includes objective and climatologically significant measures of thermal climate impact (i.e., metadata) captures in general the range of landscapes in city regions around the world gives standardized surface types for assessing UHI intensity 12

13 Suggestions and Possible Solutions for Re-defining UHI Magnitude Previous Attempts at Landscape Classification: Based on land use (Auer, 1978) building geometry (Ellefsen, 1990/1) surface roughness (Davenport et al., 2000) surface cover, geometry, and roughness (Oke, 2004) 13

14 METADATA CLIMATE ZONE CLASSIFICATION Urban Climate Zones (Oke 2004) UHI TYPOLOGY Guangzhou, CHINA sky view impervious cover surface roughness soil moisture albedo artificial heat Artificial Disturbance minimal moderate maximum ZONE a b c d e Agricultural Climate Zones f g h i j Bioclimatic Zones k l m n Yuma, ARIZONA UHI magnitude T(zone a-f) UHI magnitude T(zone c-o) ZONE o 14

15 Conclusions The urban-rural divide is distracting us from recognizing the surface types and temperatures that actually determine UHI intensity. A new landscape classification scheme will discourage unsubstantiated inter-city comparisons of UHI intensity. The framework will reduce variability in the landscapes sampled for UHI observation; it will bring organization to the existing UHI literature; and it will improve communication of UHI results. 15