Advancing heat wave definitions: a policy review towards prioritizing health impacts of extreme heat

Abstract

Approaches to defining a heat wave vary globally. While they are mostly meteorology-centric, there is an increasing need to consider their health implications. Our methodology involved a review of biometeorological indices, followed by a systematic policy search of country-level heat wave definitions to explore the variability of heat protection mechanisms. We analyzed the regional coverage of heat wave definitions and warnings by examining the diversity of variables and threshold limits for 112 countries/territories. We identified the upper-most heat stress limits of biometeorological indices that trigger illness or death. The findings highlight that a large proportion of countries define heat waves based solely on maximum temperature, while only a few countries combine them with minimum temperature and/or humidity. We also find significant geographical variability in the incorporation of temperature limits with most countries in northern latitudes defining heat waves at lower thresholds. We highlight the need for policy reforms towards adjustment of heat warning thresholds to regionally appropriate levels considering rising extreme heat conditions. Given the predominance of maximum temperature-centric approaches, we argue that the focus of heat protection at the policy level must shift beyond projecting heat wave episodes and consider broader heat-health associations beyond mortality.