Effect Modification of Heat Wave Characteristics and Influence on Variability in Mortality in Northwestern India

摘要

While the relationship between heat waves and health has been studied, questions remain regarding health effects of heat waves that occur in climates with high baseline temperatures, especially under a changing climate. Additionally, questions remain regarding causal inference, and whether prior results for high effects early in season apply universally. Few studies have assessed the relationship between heat waves and health outcomes in India and no study assessed how heat wave characteristics, including intensity, duration and seasonality, influence the health burden associated with heat. Data from city registrars and local meteorological departments were collected (period 2000-2012, varying by community) for 4 communities in Northwestern India. Propensity Score Matching (PSM) was used to obtain attributable mortality and relative risk of mortality in regards to a variety of heat wave definitions (n=13) incorporating heat waves' duration, intensity as well as timing in season. Relative risk of heat waves (risk of mortality comparing a heat wave day to matched a non-heat wave day) ranged from 1.28 [95% CI: 1.11,1.46] in Churu to 1.03 [95% CI: 0.87,1.23] in Idar and Himmatnagar. Some heat wave definitions resulted in a high relative risk of deleterious health effects, however so few days match those criteria that the absolute health burden was small. Heat waves that occurred later in season were much more deleterious to health, contributing to more attributable deaths than early season heat waves. Heat waves have harmful health effects even in places with high baseline temperatures, and the effect of heat waves varied by heat wave definition as well as by health endpoint. Unlike previous studies, heat waves occurring later in season were more harmful across the study area. These findings are critical from a policy perspective, as a tool for policy makers to determine the most important local criteria for declaring a heat wave.