Spatial Variability of Summer Temperature and Related All-cause Mortality from 2006 to 2015 for Indian Cities: A Time Series Analysis

Abundant literature is available on an extremely high temperature associated with mortality for cities of the developed world, but there is a dearth in the literature for coastal, desert and dry cities of the developing world, especially for India. We examined all-cause mortality and extreme high temperature in three Indian cities representing coastal, desert and dry areas for summer months (March to June) from 2006 to 2015. We obtained the data on temperature and all-cause mortality for ten years for the summer months. The city-specific effect of ambient heat on all-cause mortality was assessed through time series ordinary least square linear regression model. A total of 75,571, 122,117 and 53,042 deaths for 1,203, 1,220 and 1,180 summer days from 2006 to 2015 were analysed with ambient temperature for Jaipur, Hyderabad and Surat, respectively. There were 994 (27.6%) out of 3,603 summer days having temperature ≥40°C and 2,495 (69.3%) out of 3,602 summer days having feel temperature/heat index (HI) of ≥41°C. According to the Indian Meteorological Department (IMD) criteria for the heatwave, Surat has the maximum number of 75 days with a maximum temperature of ≥40°C, whereas Hyderabad has only 4 days and Jaipur faced 35 days with a maximum temperature of ≥45°C during the study period. The per-day mean all-cause mortality increased to 39% and 11% for Jaipur and Hyderabad, respectively, at ≥45°C and 20% for the coastal city of Surat at ≥40°C as per IMD heatwave criteria. A time-series linear regression model shows that adjusted R-squared is 0.593, 0.629 and 0.348, which explained the variation of 59.3%, 62.9% and 34.8% for all-cause mortality (dependent variable) by independent variables (maximum temperature, humidity and HI) for Jaipur, Hyderabad and Surat, respectively. The maximum temperature threshold (cut-off) for all-cause mortality for Jaipur, Hyderabad and Surat is 42°C, 41°C and 40°C, respectively. The impact of ambient heat in the rise of all-cause mortality for all study sites was evident. Hence, findings support the efforts for reducing the public health burden of high ambient temperature through developing and implementing city-specific heat action plans.