Heat-Related Mortality: Defining Thermal Markers for a Heat Alert System in Belo Horizonte, MG, Brazil

Abstract

Objective: To estimate daily maximum temperature markers for defining heatwave alert levels in Belo Horizonte.
Methods: A time-series study (2014–2024) was conducted using daily air temperature data from the Pampulha automatic weather station of the National Institute of Meteorology and all-cause mortality data from the Mortality Information System. The association between daily maximum temperature and mortality was estimated using quasi-Poisson regression with distributed lag non-linear models, considering lags from 0 to 21 days and adjusting for long-term trend, seasonality, and day of the week. The minimum mortality temperature was used as the reference for estimating relative risks, and high percentiles of temperature were used to define operational thresholds.
Results: The minimum mortality temperature was 29.3°C. Mortality risk increased progressively at higher percentiles, with relative risks of 1.04 at the 90th percentile, 1.09 at the 95th percentile, 1.17 at the 98th percentile, and 1.26 at the 99th percentile. Four alert levels were proposed by combining maximum temperature thresholds and thermal persistence: level 1 (≥32.0°C), level 2 (≥33.1°C), level 3 (≥34.6°C), and level 4 (≥35.8°C). A higher frequency and intensity of heatwaves were observed in years associated with the El Niño phenomenon.
Conclusion: Alert markers based on high percentiles of maximum temperature combined with thermal persistence produced levels consistent with the increase in mortality risk in the municipality, with potential application in public health surveillance and response.