Evolution climatique et canicule en milieu urbain : apport de la télédétection à l'anticipation et à la gestion de l'impact sanitaire

rapport finalSummer warming trends in Western Europe are increasing the incidence, intensity and duration of heat waves. These are especially deadly in cities owing to surface properties, anthropogenic heat and pollutants. In August 2003, for nine consecutive days, the Paris metropolitan area experienced an extreme heat wave that caused 4,867 heatrelated deaths. A time series of 84 satellite thermal images, from July 21 to August 21 2003 was used to analyze surface temperature variations and the associated heat stress. Satellite observations indicate significant surface temperature gradients and contrasted daytime / nighttime urban heat island patterns. The relatively small temperature amplitude in reference to a normal summer confirms the impact of high minimum temperatures on the heat wave process, lack of nighttime relief and on the subsequent heat stress and mortality. Maps of temperature thresholds and areas most vulnerable to heat stress were delineated. Thermal indices were produced at the addresses of 482 case studies and were integrated into a regression model to estimate the risk factors of mortality for elderly people during the heat wave. Thermal indices for minimum, maximum, mean surface temperatures and diurnal amplitude were tested on the day of death and 1, 2, 6 or 13 days preceding. Results from the linear regression analysis were statistically significant for minimum temperatures. For an increase of 0.5°C, the death risk can be twice as high. A summertime satellite surveillance is being developed to inform the public and authorities about extreme surface temperatures and related heat stress. This analysis demonstrates the relevance of satellite remote sensing in monitoring heat waves in megacities, in estimating the health impact and implementing alert systems and public health strategies