Physically-based modeling of topographic effects on spatial evapotranspiration and soil moisture patterns in complex terrain

Abstract

Simulation with the Soil Water Atmosphere Plant (SWAP) model is performed to quantify the spatial variability of evapotranspiration (ET) and soil moisture content (SMC) caused by topography-induced spatial wind and radiation differences. The field scale SWAP model is applied in a distributed way, i.e. for each grid, assuming linear groundwater table, identical boundary conditions and no lateral flow. Input of spatial wind and solar radiation are obtained with the adapted r.sun model and the meso-scale METRAS PC model based on physical mechanisms respectively. Both potential and actual ET, as well as the individual components of evaporation and transpiration are calculated by the model. The numerical experiments are conducted for grids at two different resolutions (100 m and 1000 m) to evaluate the scale effects. At fine scale, both solar radiation and wind have a strong effect on spatial ET/SMC pattern, whereas at coarse scale, the wind effect dominates. The results show a strong spatial and temporal intra-catchment variability in daily/annual total ET and less variability in soil moisture. The spatial variability in ET is associated with a difference in total amount of runoff generated, which may lead to a significant consequence in catchment water balance, snowmelt and rainfall-runoff generation processes.