Heat waves' impacts and responses, answering a call to action

After the 1995 Chicago heat wave, S.A. Changnon assessed the causes of heat related deaths, and issued a call to action. He questioned the local warning system which, based on data from airport weather stations, does not represent the intra-urban temperature variations to which people are exposed. He also pointed to the lack of information concerning both the urban heat islands' delineation and magnitude and the vulnerability of the elderly population to heat stress. These issues are relevant given that climate models for the 21st century predict a year-to-year variability of summer temperatures leading to a significant increase in the occurrence, intensity and duration of heat waves. This study looks at the heat wave impacts in Paris and London over the last decade, particularly in the years 2003, 2006, 2010 and 2013. The methodology includes the analysis of land use and climate data from in-situ and satellite sensors, and public health statistics. The work addresses: 1) the regional processes that allow researchers to predict drought; 2) the spatial and temporal variability of urban surface temperature and related risks of heat-stress and mortality; and 3) the summertime urban climate monitoring and public health surveillance. The results demonstrate: 1) the contribution of urban heat islands to intensifying the heat wave and progressively raising the minimum nocturnal temperature, which is linked to heat-stress and mortality; 2) the influence of night-time temperatures and the local impact of heat exposure and duration on the death of elderly people; 3) the cooling impact of urban parks; and 4) the relevance of radiant surface temperature in assessing heat related stress. The assimilation of remote sensing data into numerical models allows us to anticipate and manage the health impact of extreme heat, and to evaluate appropriate climate responses and adaptation strategies.