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

Various components of the land surface, their individual hydrological proce sses and the process-oriented models are reviewed in this paper, with the f ocus on their application in global climate models (GCMs). The Biosphere-At mosphere Transfer Scheme (BATS) is examined regarding its performance for t hree different surfaces (crop, forest and grass), with available data from HAPEX-MOBILHY, ABRACOS and Russian data sets. The simulations of the key la nd surface prognostic variables, such as soil moisture and snow cover, are examined in detail because such validation has been lacking. Using the HAPE X-MOBILHY data, the impact of errors in the forcing variables on the uncert ainties in the partitioning of total run-off and evapotranspiration is inve stigated, and the influence of the periodic forcing on soil moisture simula tions is examined. Furthermore, an alternative empirically based approach f or 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 re alism of the overall framework of BATS, its inclusion in a GCM [the Nationa l Center for Atmospheric Research (NCAR) Community Climate Model (CCM)] lea ds to reasonably realistic simulations of surface hydroclimatological varia bles. Further improving surface hydrology in global climate models is depen dent on thorough tests of the available models using the available data, on the collection of long-term, seasonal, high-quality data, both at point an d on larger spatial scales, and on the effective representation of the surf ace types on GCM scales. (C) 1998 Elsevier Science B.V. All rights reserved .