Mortality rate and relative strain index in Buenos Aires city.

Thermal stress may seriously affect human health to the extent of provoking death in those human groups at high risk such as little children and elderly persons. This research studies the climatology of the relative strain index (RSI) in the city of Buenos Aires (Argentina). It is observed that the conditions at 1400 hours local time on more than 75% of summer days cause discomfort, though only on 25% of days are physiological failure levels reached. The nocturnal RSI values show 75% of nights to be comfortable, bringing relief and allowing physiological recuperation. Comparison between the RSI frequency distributions of different decades by the application of the Kolmogorov-Smirnov test shows a possible urban heat-island effect that increases nocturnal RSI values. The relationship between the RSI and the daily number of interments is also analysed. Because of the large number of different causes of mortality, only about 10% of the variance of the daily number of interments can be explained by the RSI value at 1400 hours local time 1 or 2 days before. Comparison of mortality figures with these RSI values shows deaths to be at a minimum for the interval 0.0-0.1 (the RSI comfort range), slightly increasing for negative values that could represent unexpected Summer cold waves. For values of RSI over 0.2 the increment is more abrupt, indicating an impact of a thermal strain on mortality. The relationship between the joint occurrence of the 1400 hour and 0200 hour (local time) RSI values and mortality shows a clear impact of prolonged exposure to uncomfortable conditions.