Abstract
This study investigates the synergistic effects of climate and land use change on heat index extremes in the Gediz River Basin (Mediterranean region), with emphasis on risk mapping and assessment. The research advances beyond conventional approaches by jointly evaluating the contributions of climate dynamics and land use transformations to the heat index, a critical indicator of thermal stress. To capture land use influences, land surface temperature values were statistically adjusted for air temperature and then classified into risk groups, which were integrated with heat index-based health risk categories. Using land surface temperature, air temperature, relative humidity, and land use data, composite risk maps were developed for the baseline (1960–2024), near-future (2050–2075), and far-future (2075–2100) periods. Findings reveal that under baseline conditions, the basin already faced moderate to high vulnerability (Extreme Caution-EC+ to Danger-D++). Projections under the RCP 8.5 scenario indicate a progressive intensification of risk, with the entire basin surpassing the D++threshold by the far future, underscoring the dominant role of climate change. Land use changes, driven by urban expansion, deforestation, and agricultural intensification, further exacerbate localized risks, though their effect remains secondary to climate change. These results highlight the urgency of adaptive strategies that couple climate change mitigation with sustainable land and urban planning.