The Torne-Kalix PILPS 2(e) experiment as a test bed for modifications to the ECMWF land surface scheme

Results from two land surface models participating in the PILPS 2(e) experiment [the default European Centre for Medium-Range Weather Forecasts (ECMWF) scheme and a modified version labeled MECMWF] are examined. Modifications are implemented in the parameterization of snow sublimation, albedo ageing, surface runoff, and soil hydraulical coefficients. Results of a third run, SECMWF, in which the snow changes were incorporated but the runoff and soil changes were not, were also included in the analysis. Comparison of the model results to observed catchment averaged discharge and the hydrological balance inferred from it showed a pronounced improvement of the annually averaged partitioning of precipitation over evaporation and runoff. The changes were mainly a result of a reduced snow sublimation by an increased aerodynamical resistance. Comparison to measured discharge from individual calibration basins revealed that the surface runoff parameterization resulted in improved temporal dynamics of discharge from the mountainous Abisko catchment, but it deteriorated results from the low Lansjärve basin. This was not only due to a miscalibration of the surface runoff parameterization, but probably requires an appropriate estimation of deep bottom drainage. Local calibration of soil hydrology appears mandatory for obtaining a better temporal characterization of discharge. For the basin simulations considered, annual averaged runoff is fairly insensitive to the partitioning of runoff over a surface component and a deep drainage term.