Effect of ambient heat on all-cause mortality in the coastal city of Surat, India

A wealth of information is available on extreme heat and humidity associated with mortality for cities of the developed world, but there is a dearth in the literature for coastal cities of the developing world. The aim of the present study was to assess the effect of ambient heat on all-cause mortality on the urban population of Surat, a coastal city in India. Retrospective analysis of all cause mortality data with temperature and humidity was performed for the summer months (March-May) for the period 2001-12. Student's t-test and correlation coefficient were used to study the relationship between ambient heat and mortality. A total of 36,167 deaths for 961 summer days (2001-12) were analysed. Mean daily mortality was estimated at 37.6 +/- 9.4 for the study period. There is an increase of 11% mortality when the temperature crosses 40 degrees C. However, there is an increase of 3 (9%) deaths per day during danger-level heat-risk days and 6 (18%) deaths per day during high-risk heat days (extreme danger) respectively. Mortality seems to be well correlated with the high temperature (P < 0.001) and high heat index (HI) values (P < 0.001). The effect of extreme heat on mortality is at a peak on day-2 of the maximum temperature. The study concludes that the impact of ambient heat in the increase of all cause mortality is clearly evident and HI is more important than maximum temperature (18% deaths/day versus 11% deaths/day). Therefore, emphasis should be given to develop measures of adaptation towards ambient heat. This analysis may fulfil the needs of policy makers and apply strategies like integrated coastal zone management. Extreme heat-related mortality merits further analysis in order to reduce harmful health effects among Surat's most vulnerable urban population.