An equivalent cross-sectional basis for semidistributed hydrological modeling

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The computational effort associated with physically based distributed hydrological models is one of their major limitations that restrict their application in soil moisture and land surface flux simulation problems for large catchments. In this work, a new approach for reducing the computational effort associated with such models is investigated. This approach involves the formation of equivalent cross sections, designed in a manner that ensures comparable accuracy in simulating the hydrological fluxes as a fully distributed simulation. Single or multiple equivalent cross sections are formulated in each Strahler's first-order subbasin on the basis of topographic and physiographic variables representing the entire or part of the subbasin. An unsaturated soil moisture movement model based on a two-dimensional solution of the Richards' equation is used for simulating the soil moisture and hydrologic fluxes. The equivalent cross-section approach and the model are validated against observed soil moisture data in a semiarid catchment and found consistent. The results indicate that the equivalent cross-section approach is an efficient alternative for reducing the computational time of distributed hydrological modeling while maintaining reasonable accuracy in simulating hydrologic fluxes, in particular dominant fluxes such as transpiration and soil evaporation in semiarid catchments.