Is land surface processes representation a possible weak link in current Regional Climate Models
The representation of land surface processes and fluxes in climate models critically affects the simulation of near surface climate over land. Here we present an evaluation ofCOSMO CLM2, a model which couples theCOSMO CLM Regional Climate Model to the Community Land Model (CLM4.0) CLM4.0 provides a more detailed representation of land processes compared to the native land surface scheme in COSMO CLM.Weperform historical reanalysis driven simulations over Europe with COSMO CLM2 following the EURO CORDEX intercomparison protocol.Wethen evaluate simulations performed withCOSMO CLM2, the standard COSMO CLM and other EUROCORDEXRCMs against various observational datasets of temperature, precipitation and surface fluxes. Overall, the results indicate thatCOSMO CLM2 outperforms both the standard COSMOCLMand the other EURO CORDEX models in simulating sensible, latent and surface radiative fluxes as well as 2 meter temperature across different seasons and regions. The performance improvement is particularly strong for turbulent fluxes and for daily maximum temperatures and more modest for daily minimum temperature, suggesting that land surface processes affect daytime even more than nighttime conditions.COSMO CLM2 also alleviates a long standing issue of overestimation of interannual summer temperature variability present in most EURO CORDEX RCMs. Finally, we show that several factors contribute to these improvements, including the representation of evapotranspiration, radiative fluxes and ground heat flux. Overall, these results demonstrate that land processes represent a key area of development to tackle current deficiencies in RCMs.