Variability and impacts of hydrometeorological variables on surface water resources in Mokolo river catchment, South Africa

Abstract South Africa’s water resources are increasingly threatened by climate variability and climate change, particularly in semi-arid regions such as the Mokolo River Catchment in Limpopo Province. This study analyzed 30 years (1990–2020) of monthly rainfall, temperature, and streamflow data to assess variability and trends using the Modified Mann-Kendall and Sequential Mann-Kendall tests. Results revealed a statistically significant decreasing trend in rainfall ( p < 0.05) across all seven monitoring stations and a significantly increasing trend in temperature ( p < 0.05). Temperature variability was moderate (CV = 19.7%), while rainfall and streamflow exhibited much higher variability, with coefficients of variation exceeding 130% and 350%, respectively. The highest recorded streamflow (133.8 m 3 /s) at Station A4H005 occurred in February 1996, corresponding with peak rainfall, highlighting the direct relationship between rainfall and runoff. Streamflow at Station A4H010 showed a significant decreasing trend ( p < 0.05), whereas other stations exhibited mixed trends, likely influenced by local land use and geomorphology. The 1992/1993 drought reflected markedly low flows across all stations. The results reveal rainfall as the primary driver of hydrological responses in the catchment, although rising temperatures intensify evapotranspiration losses, further stressing water resources. The findings advocate for integrated, climate-resilient water management strategies to ensure the sustainability of the Mokolo River’s vital services.