Heat Exposure Definitions in Temperature-Mortality Studies: Towards a Harmonisation Framework

We reviewed how heat exposure is defined using thresholds and reference temperatures derived from the temperature-mortality exposure-response curve in time-series and case-crossover studies using distributed lag non-linear models and propose a harmonisation framework relevant to climate change research and heat disaster preparedness.

The rapid review identified variation across studies in heat thresholds and reference temperatures, affecting the comparability of estimates. A case study in Spain illustrates how the minimum mortality temperature (MMT) approach estimates overall heat-related mortality and its contributions from moderate and extreme heat, whereas the percentile-based approach estimates excessive heat mortality that could potentially be prevented by protective measures operating above the heat threshold. Differences in heat thresholds and reference temperatures make findings harder to compare across studies and complicate risk communication. Explicit reporting of these two components and their relevance to the research question and intended application would improve interpretation and translation to public health action.