Future Changes in Extreme Heat Events and Their Impacts on Mortality Using Kilometer-Scale Global Climate Simulations

Extreme heat events pose significant threats to global public health, yet their future impacts remain uncertain due to the coarse spatial resolution of current climate models. This study investigates the effect of horizontal resolution of heatwave projections and related mortality risks using the coupled Earth system model OpenIFS-FESOM2 (AWI-CM3) with atmospheric resolutions of 9 km (TCo1279; HR) and 31 km (TCo319; MR).

Model validation based on the Spherical Convolutional Wasserstein Distance (SCWD) shows that the HR simulation more accurately captures observed temperature patterns over North America, Europe, and Australia. While both simulations accurately capture the heatwave distributions, the HR simulation shows improved agreement with observations. The HR simulation projects a substantial increase in heatwave frequency and duration toward the late 21st century. In densely populated regions such as Europe and East Asia, heatwave frequency and spatial extent are projected to increase rapidly, with prolonged events exceeding 100 days by the 2090s. Assessments of heatwave-related mortality risk consistently indicate substantial future increases, with broadly similar spatial distributions across both simulations. However, city-level discrepancies emerge due to variations in model resolution, highlighting the superior performance of high-resolution simulations in detecting and projecting heatwaves at the urban scale.