A tale of five cities: heat waves, cold spells and mortality risk in urban India

Abstract

Background: Temperature extremes as a consequence of changing climate are known to have large morbidity and mortality impacts. Studies assessing mortality risk due to heat waves and cold spells are largely absent in urban India. Addressing this gap is critical in developing adaptation measures to protect the health of vulnerable populations in urban India. Methods: Daily all-cause mortality, temperature and humidity data were collected for five cities – Ahmedabad, Bangalore, Hyderabad, Mumbai and Shimla spanning 2005 - 2012. We developed Poisson regression models to study ‘the main temperature effect’ as well as ‘additional impacts’ of sustained high and low temperatures (i.e. heat and cold waves) on all-cause mortality risk. Results: We find large heterogeneity among mortality risks across urban areas. Typically, risks increase with intensity of heat (cold) waves. Populations in hotter environments may be more susceptible to cold related impacts and vice-versa. Across urban areas the main temperature effect captures most of the mortality risk. We find that ‘additional impacts’ due to sustained temperatures (heat and cold waves) is not significant. Conclusions: This is one of the first multi-city studies to examine mortality risk due to heat and cold waves in Indian cities that are spread across climatic regions and topographies. Our findings highlight the need for developing planned adaptation measures in Indian cities to minimize health impacts.