Abstract
Abstract. Recently, new soil data maps were developed, which include vertical soil properties like soil type. Implementing those into a multilayer Soil-Vegetation-Atmosphere-Transfer (SVAT) scheme, discontinuities in the water content occur at the interface between dissimilar soils. Therefore, care must be taken in solving the Richards equation for calculating vertical soil water fluxes. We solve a modified form of the mixed (soil water and soil matric potential based) Richards equation by subtracting the equilibrium state of soil matrix potential ψE from the hydraulic potential ψh. The sensitivity of the modified equation is tested under idealized conditions. The paper will show that the modified equation can handle with discontinuities in soil water content at the interface of layered soils.
Highlights
The Richards equation (RE) (Richards, 1931) is commonly used in many Land Surface Models (LSMs) to describe vertical soil water flow in unsaturated zones
If the water table depth (WTD) is below the model domain (3 m and 5 m), fluxes only occur at the interfaces between different soil horizons (Fig. 2)
That below and at saturated layers, huge fluxes occur up to 230 mm h−1. They especially occur at the interfaces between different soil horizons as a result of the influence of different soil properties and this shows that the mixed form of RE is not adequate in simulating water flows in saturated soils
Summary
The Richards equation (RE) (Richards, 1931) is commonly used in many Land Surface Models (LSMs) to describe vertical soil water flow in unsaturated zones It is a combination of mass conservation and Darcy’s law. Zeng and Decker (2008) applied a modified mixed form of RE for unsaturated homogeneous soils, where mass conservation is nearly given We expected, that this combination will lead to better results in modeling water flows in inhomogeneous soils and herefore, implemented this formulation into the LSM model TERRA-ML, which is included in the non-hydrostatic mesoscale weather forecast model COSMO (http://www.cosmo-model.org/) as well as in the regional climate model COSMO-CLM (http: //www.clm-community.eu/). Ahrens: The mixed form of Richards equation and its application in vertical inhomogeneous soils
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