Simulating Root Water Uptake from a Heterogeneous Vegetative Cover

Abstract

A small body of knowledge exists on the root water uptake (RWU) and evapotranspiration in humid environments having a mixture of natural vegetative cover. In this paper, we assess the impacts of atmospheric conditions and land cover on RWU from a natural vegetative cover. An intensive field investigation was carried out to monitor water table fluctuations along two flow transects comprising an upland grass area and a lowland riparian zone. Calibration and validation of the soil hydraulic parameters using the two-dimensional variably saturated ground water flow model, HYDRUS-2D, confirms the reliability of the model to simulate satisfactorily the large-scale daily fluctuation of RWU. Simulation results revealed that the actual RWU during the wet season is about 40% higher than RWU in the dry season due to high water table levels and temperatures prevailing throughout the wet season. Simulation results using HYDRUS-2D, which was modified to accommodate variable surface boundary conditions and heterogeneous root distribution, showed that the RWU from the riparian zone was 38 and 56% higher than RWU from the pasture land during the dry and wet seasons, respectively.