A new approach to modelling streamflow reductions resulting from commercial afforestation in South Africa

Abstract

Synopsis The Department of Water Mfairs and Forestry has, for some time, needed a comprehensive tool to incorporate the impacts of commercial afforestation on water resources into water use authorisation and allocation processes. Simulation modelling on a national scale, using the ACRU model, was identified as one possible solution. However, in order to establish confidence in the national simulation results, it was necessary to first verify model output against reliable observed data from process studies and long-term catchment afforestation experiments. In the verification phase, long term reductions in streamflow resulting from afforestation were satisfactorily simulated for five research catchments. Some problems were experienced with catchments in the Western Cape, with verifications on shorter duration experiments and the simulation of specific evaporative processes. Modelling oflow flows was less successful than for total flows. In the second phase (the generation of the national database), simulat...