Understanding the impact of climate change on agricultural nonpoint source (NPS) pollution is crucial for developing effective adaptation strategies and reducing vulnerabilities where such challenges exist. This study evaluated the impact of precipitation and temperature variations on Total Inorganic Nitrogen (TIN), Total Inorganic Phosphorus (TIP), and sediment loads in the Sand River Catchment (SRC) using the Soil and Water Assessment Tool plus (SWAT+). One-way analysis of variance (ANOVA) was used to determine the significance (p < 0.05) of the relationships (R²) between precipitation and temperature on sediment, TIN, and TIP loads in the SRC. SWAT+ calibration and validation demonstrated that the statistical indices (NSE and R² ≥ 0.72; −17.30 ≤ PBIAS ≤ 14.74) fell within an acceptable range. Results indicated a significant influence of average monthly precipitation (p < 0.0001) and temperature (p ≤ 0.004) on sediment, TIN, and TIP loads. In addition, a decrease in average annual precipitation led to a decline in sediment, TIN, and TIP loads (R² ≥ 0.55), with the average annual temperature increasing in the same period (R² ≤ 0.23). This study confirms that climate change contributes to agricultural NPS pollution in the SRC and highlights the need to employ suitable adaptation strategies for pollution control in the catchment.

Climate-induced drought increasingly threatens water security in semi-arid regions, as rising temperatures become the primary driver of hydro-climatic variability. This study assessed long-term drought dynamics in the Nzhelele River Catchment (NRC), through Mann–Kendall (MK) trend analysis, Sen’s slope estimation, and the Standardized Precipitation Evapotranspiration Index (SPEI) for the period from October 1994 to September 2024. Aggregated in situ weather station data and 0.25° × 0.25° gridded climate node (GCN) datasets were used to quantify trends in mean annual temperature, potential evapotranspiration (PET), and precipitation. The results revealed a statistically significant warming trend of 0.037 °C/yr. and an increase in PET at an average of 6.343 mm/yr., while precipitation showed a weak, non-significant decline (–0.568 mm/yr.). SPEI analysis identified recurrent severe droughts between 2003 and 2009; 2010–2013; 2014–2016; and 2018–2020, with the 2014–2016 period as the most extreme climatic stress. Gridded SPEI aligns closely with station-derived SPEI across all accumulation scales (R² = 0.76–0.87; p-value < 0.001), supporting the use of ERA5-based climate products for drought monitoring in data-scarce regions. Due to the limited number of in situ stations and spatial averaging inherent in gridded datasets, the results provide an approximate representation of hydro-climatic conditions across the catchment. Overall, the findings indicate a shift toward temperature-driven drought regimes, growing climate risks to water availability, and the need for climate-resilient water resource planning.

The intensified use of chemical fertilisers, coupled with unmanaged agricultural land, results in nonpoint source (NPS) pollution of surface water resources through runoff. This study aimed to evaluate the effectiveness of Best Management Practices (BMPs), including grassed waterways (GWW) and vegetative filter strips (VFS), and their combination in reducing sediment, total inorganic phosphorus (TIP), and total inorganic nitrogen (TIN) loads in a catchment under semi-arid conditions. Furthermore, the study sought to compare the performance of these BMPs when implemented at the catchment level versus the sub-catchment level. The Soil and Water Assessment Tool (SWAT+) was used to simulate annual TIN, TIP, and sediment loads under various scenarios (base, GWW, VFS, and GWW + VFS) in the Sand River Catchment (SRC). A percentage reduction equation was applied to determine the load reductions achieved in each scenario. Calibration and validation of the SWAT+ model showed good performance, with R² and NSE values above 0.72 indicating strong correlation, and PBIAS values (− 17.30 to 14.74) within acceptable limits, confirming model reliability. The simulated results have revealed a lower reduction in sediment, TIP, and TIN loads using VFS at sub-catchment and catchment levels (27/23%, 23/20%, and 30/25%, respectively), compared to GWW (47/38%, 35/31%, and 43/31%, respectively). VFS + GWW exceedingly reduced sediment, TIP, and TIN loads at the sub-catchment level as compared to the catchment level (70/58%, 66/56%, and 71/62%, respectively). The study concludes that implementing BMPs at the sub-catchment level can be one of the most effective management strategies for NPS pollution in the SRC.