Modelling the impact of climate variability and land-use changes in the Upper Crocodile River Basin, South Africa

Fynn, Byron Melvin
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Improved understanding of the impacts of climate and land-use changes on water resources in the semi-arid conditions of South Africa is necessary to ensure their sustainability. In this study, the Soil and Water Assessment Tool (SWAT) was applied to the highly urbanisedUpper Crocodile River Basin (UCRB) to evaluate the individual and combined effects of climate and land-use changes on streamflow. The SWAT model was calibrated against six discharge stations from 1998 to 2010 and validated from 2010 to 2016. Successful results regarding the coefficient of determination (R2), percentage bias (PBIAS), and Nash-Sutcliffe efficiency equation (NSE) objective functions against four discharge stations for the calibration and validation periods proved that streamflow predictions were reliable for analysis under climate and land-use changes. The climate change scenarios, reflecting a 1.5 °C temperature increase, and a 20% precipitation decrease, were shown to reduce the antecedent moisture condition of the UCRB. The 5% urban expansion land-use scenario revealed that increasing urbanisation enhanced theimperviousness of the basin. Moreover, in the worst-case scenario, incorporating the climate and land-use changes resulted in a 14% average streamflow decrease in the UCRB. Consequently, the UCRB's predicted climate and human activity changes suggest water availability and quality decreases. Surface water quality will be aggravated as there is less natural water for the dilution of effluent loadings, and groundwater quality may be exacerbated by its connection with surface water in the basin. Therefore, enhanced integrated water management strategies, above those currently considered, is required to ensure the efficient use and sustainability of the UCRB's water resources.
A research report submitted to the School of Geosciences, Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Hydrogeology, 2022