Soil moisture dynamics in the Velen drainage basin (Sweden) were analyzed in order to assess the degree of and the reasons for spatial variation in basin behaviour. The main tool was a modified version of the soil moisture accounting routine in the conceptual runoff model HBV, optimized against neutron probe field data. Simulated soil moisture dynamics, interception and percolation rates agreed well with measurements and other calculations. Integration of simulated evapotranspiration from sites with different characteristics agreed well with water balance computations for the area. It was shown that unsaturated flow through macropores probably occurred after heavy rainstorms. During spring, evapotranspiration was limited to values below the potential (Penmans equation) even at times when no soil moisture deficit existed. Soil moisture differences between forest and grassland (including a deforested site) were, during summer, mainly attributed to differences in the root distribution with depth. The effect of interception on the total evapotranspiration rates was only significant during periods when transpiration demands were low. Soil moisture differences between forest sites were mainly attributed to topography but variations in soil characteristics and root distribution had to be considered, especially during dry periods.

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