Spatial Heterogeneity in Heat-Related Mortality in the Valencian Region: Implications for Climate Adaptation Beyond Administrative Boundaries.

The intensification of extreme heat events in the Mediterranean basin poses growing threats to public health, particularly in climate-vulnerable regions like the Valencian Region (eastern Spain). Despite the implementation of provincial and municipal heat prevention plans, their efficacy remains unevaluated, and most studies have focused on provincial capitals, potentially overlooking subregional variability. This study addresses these gaps by quantifying moderate and extreme heat-attributable mortality across 28 thermoclimatic areas (TAs)-a climatic subdivision of the Valencian Region- from 1975 to 2019, using a two-stage time-series analysis of high-resolution temperature and mortality data. Results reveal a distinct coastal-inland gradient, with significantly higher mortality impacts in inland TAs compared to coastal provincial capitals. Areas most impacted by extreme heat are concentrated in interior regions, while coastal capitals exhibit lower risks. These findings underscore the limitations of relying on administrative boundaries for public health surveillance and adaptation planning. The study highlights the value of climatically coherent zones, such as TAs, for improving the spatial resolution of early warning systems and tailoring heat prevention strategies. This scalable methodological framework provides critical insights for enhancing the design of heat adaptation plans not only in Spain but also in other Mediterranean and climate-sensitive regions.