Approaches to defining a heat wave vary globally. While they are mostly meteorological-centric, 
there is an increasing need to consider their health implications as heat stress experienced by 
humans. 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 serious 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 considering broader heat-health associations beyond mortality by incorporating 
heat stress indices.