Inter-comparison of two land-surface schemes applied on different scales and their feedbacks while coupled with a regional climate model

Abstract

Abstract. Feedback effects between the land surface and the atmosphere are an important issue in modelling the climate system. Therefore, in order to take land surface heterogeneity adequately into account, a representation of the land surface in sufficient spatial resolution is necessary. In order to analyze the impact of different land surface models on the atmosphere, we analyzed the differences of two physically based land surface models, which evolved from different disciplinary backgrounds, both fully coupled with the regional climate model MM5, providing the atmospheric drivers. While the NOAH-LSM originally was developed for atmosphere applications, PROMET is primarily used as a hydrological land surface model. Both use different physical approaches and different spatial resolutions of 45 km (NOAH) and 1 km (PROMET) respectively, to represent the land surface processes. The parameterization of soil and plant properties in terms of phenological behaviour and water-stress is treated with a higher level of detail in PROMET. Used with same atmospheric drivers over a four-year period for Central Europe, the model differences have strong impacts on simulated evapotranspiration and soil moisture both spatially and temporally. Regions with high proportion of impervious surfaces show the highest differences in simulated evapotranspiration (up to 30 %). Further, PROMET simulations show lower evapotranspiration rates e.g. in the Po Valley, caused mainly by a higher level of vegetation water stress. In order to study feedback effects, PROMET was then bilaterally coupled with MM5. The feedbacks result in increasing near surface air temperature and decreasing precipitation especially in Southern Europe and are a result of regional self-amplification effects due to decreasing soil moisture and increasing vegetation water stress.