Investigating the Representation of Heatwaves from an Ensemble of Km-scale Regional Climate Simulations within CORDEX-FPS Convection

Abstract Heatwaves (HWs) are high-impact phenomena that stress both societies and ecosystems. Their intensity and frequency are expected to increase in a warmer climate over many regions of the world. While these impacts can be wide ranging, they are potentially influenced by local to regional features such as topography, land-cover, urbanization. Here, we leverage recent advances in the very high resolution modelling required to elucidate the impacts of heatwaves at these fine scales. Further we aim to understand how the new generation of km-scale regional climate models (RCMs) modulates the representation of heatwaves over a well-known climate change hot spot. We analyze an ensemble of 15 convection-permitting regional climate model (CPRCM, ~ 2–4 km grid spacing) simulations and their driving, convection-parameterized regional climate model (RCM, ~ 12–15 km grid spacing) simulations from the CORDEX Flagship Pilot Study on Convection. The focus is on the evaluation experiments (2000–2009) and three subdomains with a range of climatic characteristics. During HWs, and generally in summer season, CPRCMs exhibit warmer and drier conditions than their driving RCMs. Higher maximum temperatures arise due to an altered heat flux partitioning, with daily peaks up to ~ 150 W/m2 larger latent heat in RCMs compared to the CPRCMs. This is driven by a 5–25% lower soil moisture content in the CPRCMs, which is in turn related to longer dry spell length (up to double). It is challenging to ascertain whether these differences represent an improvement. However, a distribution-based maximum temperature evaluation, suggests that this CPRCMs warmer/drier tendency is likely more realistic compared to the RCMs, with ~ 70% of reference sites indicating an added value compared to the driving RCMs. Certainly, CPRCMs enhance dry conditions, with knock-on implications for summer season temperature overestimation, especially over flat terrains. Whether this improved physical representation of HWs also has implications for future changes is under investigation.