An alternative method to characterize the surface urban heat island.

Philippe Martin,Yves Baudouin,Philippe Gachon

doi:10.1007/s00484-014-0902-9

Abstract

An urban heat island (UHI) is a relative measure defined as a metropolitan area that is warmer than the surrounding suburban or rural areas. The UHI nomenclature includes a surface urban heat island (SUHI) definition that describes the land surface temperature (LST) differences between urban and suburban areas. The complexity involved in selecting an urban core and external thermal reference for estimating the magnitude of a UHI led us to develop a new definition of SUHIs that excludes any rural comparison. The thermal reference of these newly defined surface intra-urban heat islands (SIUHIs) is based on various temperature thresholds above the spatial average of LSTs within the city’s administrative limits. A time series of images from Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) from 1984 to 2011 was used to estimate the LST over the warm season in Montreal, Québec, Canada. Different SIUHI categories were analyzed in consideration of the global solar radiation (GSR) conditions that prevailed before each acquisition date of the Landsat images. The results show that the cumulative GSR observed 24 to 48 h prior to the satellite overpass is significantly linked with the occurrence of the highest SIUHI categories (thresholds of +3 to +7 °C above the mean spatial LST within Montreal city). The highest correlation (≈0.8) is obtained between a pixel-based temperature that is 6 °C hotter than the city’s mean LST (SIUHI + 6) after only 24 h of cumulative GSR. SIUHI + 6 can then be used as a thermal threshold that characterizes hotspots within the city. This identification approach can be viewed as a useful criterion or as an initial step toward the development of heat health watch and warning system (HHWWS), especially during the occurrence of severe heat spells across urban areas.

Highlights

Urban city centers tend to have higher solar radiation absorption and greater thermal capacity and conductivity than the surrounding area (Weng 2001)
Two factors led us to propose a new definition for surface urban heat island (SUHI): the complexity of differentiating between what is urban and what is rural and the questionable relevance of using an external rural or non-urban reference to estimate urban heat island (UHI) magnitude
The reference chosen for the newly defined surface intra-urban heat islands (SIUHIs) is the city’s mean land surface temperature (LST) for each of the 12 Landsat images taken during summer days between 1984 and 2011

Summary

Introduction

Urban city centers tend to have higher solar radiation absorption and greater thermal capacity and conductivity than the surrounding area (Weng 2001). These modified thermal conditions can cause the local air and surface temperatures to increase by several degrees Celsius over the simultaneous temperatures of the surrounding rural areas (Oke 1982). These urban heat islands (UHIs) result partly from the physical properties of the urban landscape and partly from the release of heat into the environment by the use of energy for human activities. During hot-weather events, UHIs exacerbate thermal stress on the most vulnerable and atrisk people, those with social or physical vulnerability (Kovats and Hajat 2008; Smargiassi et al 2009)

Objectives

Methods

Findings

Conclusion