Parameterization of hydrological processes for application to regional and mesoscale modeling

Abstract

In this paper, the hydrological module of the biophysical scheme named LAPS (Land-Air Parameterization Scheme) is presented. LAPS is designed as a stand-alone one software package that can also be used as a component of a regional/mesoscale model. It includes three modules for parameterizing hydrological, bare soil and canopy transfer processes. In the hydrological module, the direct loss of liquid water across the scheme domain boundaries is calculated taking into consideration mainly overland flow, sub-surface runoff and vertical drainage through the lower boundary. Moving from the top to the bottom of the soil, the water column has three layers, where the vertical water flow is calculated according to Darcy's law. The physical background of the equations describing the above processes is presented. The performance of the hydrological module of the LAPS scheme has been tested by a one year integration of soil moisture content, over bare soil and a soybean field. The integration over bare soil in the so-called 'no-evaporation' experiment, tested the quality of the runoff and drainage parameterization in the soil column, during the four month-period. During this test, the precipitation was specified as a heavy rain in the first half, and zero in the second part of the 120 days of integration, with the zero evaporation through out the whole period. The validity of the hydrological module of the LAPS scheme was also checked by comparing the simulated values of the bare soil water budget components with observations of the soil column extending to a depth of 1.6 m from data gathered during the HAPEX-MOBILHY experiment.