A REGIONAL HYDRQLOGICAL SOIL MODEL FOR LARGE-SCALE APPLICATIONS: COMPUTATIONAL CONCEPT AND IMPLEMENTATION

A parallelized large-scale regional hydrologic soil model (RHSM) is developed as a tool for large-scale unsaturated zone investigations. It is applied to simulate the temporal and spatial responses of the unsaturated zone and the regional water budget under the forcing of realistic precipitation and evaporation scenarios. The Richards equation is used to describe the flow movement in the vadose zone and is solved using a finite element code. The RHSM provides a way to deal with the enormous discretization demand of unsaturated flow simulation at regional scales. The relatively thin soil cover is modeled vertically by 1D line elements with adequate resolution, whereas the large lateral dimensions are modeled as coarser grid patches, the so-called influence areas. In order to achieve reasonable computation times for a single model run the independence properties of the RHSM are elegantly exploited to realize a relatively uncomplex code parallelization. The parallelized RHSM runs on Linux supported symmetric multiprocessing computers using the message passing interface (MPI). This implementation attains a high performance computation of regional scale hydro-system models. In an application study at the Beerze-Reusel drainage basin (Netherlands), a high resolution of variably saturation distributions and wet front movements are obtained for the anisotropic field using the parallel RHSM. An analysis of the computational speed-up demonstrates the performance gain of the parallel RHSM.