Resolving regional climate change with global kilometer-scale climate simulations

Accurately assessing regional climate change and its associated risks, particularly over complex terrain and coastal regions, remains challenging due to large uncertainties in conventional global climate models. Kilometer-scale coupled climate modeling offers a promising pathway by explicitly resolving mesoscale atmospheric and oceanic processes, their interactions with large-scale circulation, and air-sea coupling at regional scales. Here, we present global warming simulations conducted with the coupled OpenIFS-FESOM2 climate model (AWI-CM3) at atmospheric resolutions of 31 km (TCo319), 9 km (TCo1279), and 4 km (TCo2559), combined with a variable-resolution ocean mesh ranging from 4 to 25 km. All km-scale-resolution simulations were initialized from the trajectory of the 31 km transient simulation with the same ocean configuration. Compared to 31 km simulations, the km-scale simulations exhibit substantially enhanced regional detail, including mesoscale circulation features such as sea-land breezes, their influence on coastal climate, and a clearer sensitivity of local climate responses to global warming. Our results highlight the potential of cloud-permitting, km-scale coupled modeling to improve projections of regional climate change and extremes, advance understanding of local climate sensitivity, and support climate impact assessments and adaptation strategies.