7 - Surface Temperatures in the Urban Environment

Abstract

Climate change increases the frequency, intensity, and duration of heat waves. Here we demonstrate the application of satellite thermal-infrared sensing to monitor urban heat waves, observe the spatial variation of land surface temperature (LST) over the diurnal cycle, and estimate the risk of heat-related mortality for elderly people. The work is based on a time series of 84 NOAA-AVHRR satellite images sensed during the August 2003 heat wave, which caused 4867 excess deaths in Paris and 616 excess deaths in London. In both cities, the thermal images reveal: (1) contrast between the downtown heat island during the night and multiple hot spots in industrial areas during the day; (2) the contribution of the heat wave, which enhances the heat island and further delays night cooling; (3) the relationship between LST and surface land use/physical properties; and (4) the consistent cooling effect of vegetation. In Paris, the highest nighttime LSTs matched the highest excess mortality ratio. The LSTs were sampled at the addresses of 482 elderly people (deceased/controls) to produce thermal indicators that were integrated into a regression model. Results show the relative impact of heat exposure on the elderly population at given locations and the time lag between heat exposure and death. They indicate the predominance of nighttime temperature, with a 0.5°C increment that doubles the risk of death, in the temperature range of the heat-wave episode. The results underline the relevance of satellite monitoring of extreme heat events for contingency planning and public health decision making, and implementing climate change adaptation and mitigation strategies.