Intra-urban variation of mortality as a function of high ambient temperatures

BACKGROUND. Little attention has been paid to how heat-related health effects vary with the micro-urban variation of outdoor temperatures. Here we explore whether persons living in warmer urban places – in micro-urban heat islands, are at a higher risk of mortality during hot summer days. METHODS. Data used include 1) daily mortality for Montreal (Canada) for the summers 1990-2003, 2) daily mean ambient outdoor temperatures at the local International Airport and, 3) a single thermal surface image (Landsat-7/ETM+, infra-red wave lengths). A city-wide temperature vs daily mortality function was established on the basis of a case-crossover design; this function was stratified according to the surface temperature at decedents' place of residence. RESULTS. The risk of death during the warm season in areas with higher surface temperatures was greater than in areas with lower surface temperatures. Furthermore, in areas with higher surface temperatures, the risk of death was also greater for those who lived in low-value dwellings. CONCLUSIONS. Our study suggests that cooling centers and other social measures designed to protect public health from extreme heat should be located in priority in micro-heat islands, particularly those in areas of poverty.