International study of temperature, heat and urban mortality: the ‘ISOTHURM’ project

TLDR

This study describes heat‑ and cold‑related mortality in 12 urban populations in low‑ and middle‑income countries, extending knowledge of how diverse, non‑OECD populations respond to temperature extremes. The study aims to identify vulnerability within populations. Daily mortality in the 12 cities was examined with autoregressive Poisson models over 2‑ to 5‑year series, adjusting for seasonality, relative humidity, air pollution, day of week, and public holidays. Most cities showed a U‑shaped temperature‑mortality relationship, with cold‑related increases in all but Ljubljana, Salvador, and Delhi, and heat‑related increases in all but Chiang Mai and Cape Town; temperature thresholds ranged from 15–29 °C for cold and 16–31 °C for heat, with heat thresholds higher in warmer climates and cold thresholds unrelated to climate.

Abstract

Background This study describes heat- and cold-related mortality in 12 urban populations in low- and middle-income countries, thereby extending knowledge of how diverse populations, in non-OECD countries, respond to temperature extremes. Methods The cities were: Delhi, Monterrey, Mexico City, Chiang Mai, Bangkok, Salvador, São Paulo, Santiago, Cape Town, Ljubljana, Bucharest and Sofia. For each city, daily mortality was examined in relation to ambient temperature using autoregressive Poisson models (2- to 5-year series) adjusted for season, relative humidity, air pollution, day of week and public holidays. Results Most cities showed a U-shaped temperature-mortality relationship, with clear evidence of increasing death rates at colder temperatures in all cities except Ljubljana, Salvador and Delhi and with increasing heat in all cities except Chiang Mai and Cape Town. Estimates of the temperature threshold below which cold-related mortality began to increase ranged from 15°C to 29°C; the threshold for heat-related deaths ranged from 16°C to 31°C. Heat thresholds were generally higher in cities with warmer climates, while cold thresholds were unrelated to climate. Conclusions Urban populations, in diverse geographic settings, experience increases in mortality due to both high and low temperatures. The effects of heat and cold vary depending on climate and non-climate factors such as the population disease profile and age structure. Although such populations will undergo some adaptation to increasing temperatures, many are likely to have substantial vulnerability to climate change. Additional research is needed to elucidate vulnerability within populations.