Long-term trends and changes in rainfall magnitude and duration in a semi-arid catchment, South Africa

The study investigated long-term trends and changes in rainfall magnitude and duration in a semi-arid catchment. It is crucial to determine changes in rainfall to support efforts to adapt to climate change in highly vulnerable semi-arid areas. Trends for long-term seasonal and annual rainfall magnitude and duration were determined using Mann-Kendall (MK) and quantile regression (QR) methods. Sen's slope was used to determine the magnitude of change in rainfall. Correlation analysis was conducted to determine the influence of altitude and land-use change in rainfall trends. There were dominant non-statistically significant decreasing trends for annual, seasonal rainfall magnitude, and rainfall duration. Trends from QR at low (0.1 and 0.2) and high (0.7 and 0.9) quantiles mostly deviated from those of MK. There were weak and variable correlations of long-term rainfall trends with altitude and land-use change. Land-use change and topography may therefore not adequately explain the variations of trends. Further studies are essential to understand the interaction of environmental various factors and their influence on rainfall trends. Variations of trends will impact future water resource availability and allocation. It is important to consider the deviations when developing climate change adaptation measures and ensure improved decision-making.