The simulation of European heat waves from an ensemble of regional climate models within the EURO-CORDEX project
Abstract
The ability of a large ensemble of regional climate models to accurately simulate heat waves at the regional scale of Europe was evaluated. Within the EURO-CORDEX project, several state-of-the art models were run for a time period of 20 years over Europe.
Eight models were run in high resolution of 12 km, and thirteen models were run at a classical resolution of 50 km. All models were driven by the ERA-Interim re-analysis.
Results, which are compared with daily temperature and precipitation observations (ECA&D and E-OBS data sets), show that the ensemble exhibits a large spread. A preliminary analysis of the sources of spread shows that the simulation of hot temperature is primarily sensitive to the convection and the microphysics schemes.
Most models exhibit overestimation of summer temperature extremes in Mediterranean regions and an underestimation over Scandinavia. The simulated heat wave events were found to be too persistent, but a higher resolution reduced this deficiency.
The amplitude of events as well as the variability beyond the 90th percentile threshold were found to be too strong in almost all simulations and increasing resolution did not generally improve this deficiency. Resolution increase was also shown to induce large-scale 90th percentile warming or cooling for some models, with beneficial or detrimental effects on the overall biases.
The drivers of such regional differences were shown to be linked to changes in precipitation due to resolution changes, affecting the energy partitioning. Finally, the inter-annual sequence of hot summers over central/southern Europe was found to be fairly well simulated in most experiments despite an overestimation of the number of hot days and of the variability.
Despite some improvements, especially along coastlines, the analyses conducted here did not allow us to generally conclude that a higher resolution is clearly beneficial for a correct representation of heat waves by regional climate models.