What do kilometre-scale global simulations add to our understanding of heatwaves?

Heatwaves are a major threat worldwide, and improving their predictability and assessing their future changes are key priorities in climate research. Heatwave development arises from an interplay between large-scale atmospheric circulation, which governs persistent synoptic conditions, and smaller-scale mesoscale processes that modulate local temperature extremes. Current global climate models exhibit well-documented biases in the representation of persistent large-scale circulation patterns, such as atmospheric blocking, and are additionally unable to explicitly resolve mesoscale processes that contribute to heatwave intensity and persistence. Regional climate models can better represent some of these smaller-scale processes but remain limited in spatial coverage. Recent advances in computational capacity have enabled kilometre-scale global climate simulations, opening new opportunities to investigate heatwaves and their multi-scale drivers within a consistent global modelling framework.

Here, we analyse global kilometre-scale simulations from the EXCLAIM project using the Icosahedral Nonhydrostatic (ICON) climate model. The primary experiment consists of a global 2.5 km atmosphere-only simulation with explicit convection and prescribed daily sea surface temperatures. Companion simulations at 10 km resolution, employing both convection-permitting and convection-parameterized configurations, allow for a systematic assessment of the impacts of horizontal resolution and convection representation.

Using ICON output, we evaluate heatwave characteristics such as frequency and persistence, and examine their relationship with the associated large-scale circulation patterns. In particular, we assess the sensitivity of heatwave statistics to model resolution and convection representation. We further analyse how the well-established link between midlatitude anticyclonic blocking and heatwaves is represented across resolutions, and explore the extent to which mesoscale processes modify heatwave characteristics beyond the large-scale circulation control.

Our results provide first insights into the added value and remaining challenges of storm-resolving global climate models for understanding heatwaves, their multi-scale drivers, and their representation in a warming climate.