Effects of land surface inhomogeneity on convection-permitting WRF simulations over central Europe

This sensitivity study investigates the impact of the spatial scales of land use, soil moisture and orography patterns on land–atmosphere exchange fluxes, domain-wide averages and meteorologic conditions in convection-permitting RCM simulations. We perform five WRF RCM simulations, each with the same 3 km resolution atmospheric setup but different combinations of coarsely resolved (12 km) land use and soil type, initial soil moisture and orography for the heat-wave summer 2003 over central Europe. Our results indicate that a coarser-resolved orography significantly alters the flow over and around mountain ridges such as the Alps and impact the large-scale flow pattern. The smoothed mountain ridges result in weaker Fohn effects and in enhanced locally generated convective precipitation patterns, peaking earlier in the afternoon. In comparison, the impact of a coarser-resolved land use is smaller and mainly related to changes in the overall spatial fraction of a land use, rather than to the loss of heterogeneity of the different land use types on the scale analyzed here. Albeit, even small changes in the initial soil moisture (both spatial averages and local differences) have a higher potential to affect the overall simulation results, although this might also depend on the land surface model. Overall, effects induced by the coarsely resolved land surface properties are small compared to the differences between simulations with 3 km and 12 km grid spacings of the atmosphere.