Excess Heat and Excess Deaths: Application of Heat-Health Metrics to Assess Mortality Risk in the Limpopo Province of South Africa

Extreme heat and humidity are increasing globally, with direct implications for heat-related mortality. This study examined associations between daily natural-death counts and heat exposure in the five district municipalities of Limpopo Province, South Africa, where isolated surges in excess deaths were detected by mortality surveillance in November 2023 and December 2024. We combined spatially averaged district-level meteorological observations from 1 January 1991 to 20 July 2025 with daily mortality data from 1 January 2022 to 10 May 2025 and analysed the Excess Heat Factor (EHF) and apparent temperature (AT) in calendar-matched case-crossover models of observed death counts for all ages and ages 60 yrs and older. EHF entered the models as its positive part in local severity units. The analysis showed that absolute humidity, maximum temperature, minimum temperature and diurnal temperature range increased across districts, with the fastest proportional increases in the extreme exposure categories. At provincial level, for all ages, each severity unit of lag 0–1 EHF was associated with a mortality rate ratio of 1.191 (95% confidence interval, CI: 1.168–1.214) and extreme heatwave days carried rate ratios of 1.830 (95% CI: 1.652–2.027). Each interquartile-range increase in AT was associated with rate ratios of 1.074 (95% CI: 1.061–1.088). The EHF–mortality association was present in every district and heterogeneous in magnitude ranging from 1.092 (1.036–1.151) to 1.231 (1.169–1.296) across the districts, whereas the AT association was small and spatially uniform once EHF was included in the model. For both EHF and AT (and combined), the association with mortality was ubiquitously amplified in all models, in all districts for the 60-yrs-and-older age class. A proposed EHF-based warning was tested retrospectively and showed that both mortality surges were preceded by “warning-level” EHF alerts in every district. A district-specific, severity-based EHF alert scheme, evaluated here against the 2022–2025 mortality series, could improve municipal heat-health warning systems in Limpopo and provides a template for similar analyses elsewhere in South Africa.