Treatment of soil, vegetation and snow in land surface models: A test of the Biosphere-Atmosphere Transfer Scheme with the HAPEX-MOBILHY, ABRACOS and Russian data

Various components of the land surface, their individual hydrological processes and the process-oriented models are reviewed in this paper, with the focus on their application in global climate models (GCMs). The Biosphere-Atmosphere Transfer Scheme (BATS) is examined regarding its performance for three different surfaces (crop, forest and grass), with available data from HAPEX-MOBILHY, ABRACOS and Russian data sets. The simulations of the key land surface prognostic variables, such as soil moisture and snow cover, are examined in detail because such validation has been lacking. Using the HAPEX-MOBILHY data, the impact of errors in the forcing variables on the uncertainties in the partitioning of total run-off and evapotranspiration is investigated, and the influence of the periodic forcing on soil moisture simulations is examined. Furthermore, an alternative empirically based approach for the soil evaporation efficiency is tested. The current framework of BATS soil hydrology, vegetation and snow schemes adequately reproduces observed soil moisture profiles for the three surfaces considered, and captures the seasonal evolution of snow mass. The simulations can be enhanced when site-specific information on surface parameters is available. Because of the realism of the overall framework of BATS, its inclusion in a GCM the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM)] leads to reasonably realistic simulations of surface hydroclimatological variables. Further improving surface hydrology in global climate models is dependent oh thorough tests of the available models using the available data, on the collection of long-term, seasonal, high-quality data, both at point and on larger spatial scales, and on the effective representation of the surface types on GCM scales.