Impacts of Land Management on Water Resources in the Crocodile River Catchment, Mpumalanga

Abstract

Land use/land cover (LULC) have a “cause and effect” relationship with the hydrology of catchment areas. The Crocodile River Catchment (CRC) has been reported to be fully utilised and at its limit. Due to its ecological and socio-economic importance, it is therefore imperative to quantify the changes in the river’s water resources. Using remote sensing (RS), QSWAT and Quantum GIS (QGIS) this study analysed and evaluated the long-term effects of LULC changes on the hydrology of the CRC between 1981 and 2020. LULC was classified into 8 major classes (cultivation land, forest plantation, water, grassland, built-up areas, bush/savannah and natural forest) for 1980/81, 2000/01 and 2020 to demonstrate the changes in land-use for the past 40 years. The study found that natural forests and grassland decreased by 12.8% and 1%, respectively. There was an increase in cultivated lands, forest plantations and built-up by 2.5%, 3.1% and 2.3%, respectively. Built-up areas, cultivated lands and forest plantations were identified as the major land-use activities and the hotspots for these were further mapped and analysed per quaternary catchment. The overall NDVI value for all LULC ranged between -0.3 and 0.9. The LULC maps were used as input data to the QSWAT model to evaluate LULC impacts on water resources. The model performance evaluation showed an NSE value between 0.41 to 0.79, PBIAS -4.44 to 44.7 and RSR 0.54 to 0.75 between simulated and the observed streamflow. For this study, these findings on model performance showed acceptable results. The results further showed a decreasing trend in streamflow from1981-2020. The decreasing trends were attributed to the increase in forest plantation and cultivation with built-up areas found to have minimum impacts on the catchment’s hydrological response because they occupied a small percentage of the catchment. The distribution of ET and surface runoff also varied with the LULC, however, climate was shown to have an influence on streamflow and the distribution of LULC in the catchment area, thus affecting the hydrological regime.