Methodology for Developing Severity-Duration-Frequency Curves for Drought Assessment in South Africa

Droughts significantly affect food security, economy and livelihoods, necessitating effective water resource planning and management in South Africa. This research aimed to enhance the understanding of droughts by developing Severity–Duration–Frequency (SDF) curves using daily precipitation data. The research also addressed methodological limitations, such as data record length and gap-filling methods. Daily rainfall records from the South African Weather Service (SAWS) and Department of Water and Sanitation (DWS) with at least 30 years data were used in the development of the methodology. The methodology developed in this research used the calculation of drought indices, including the Decile Drought Index (DDI), Percentage of Normal Precipitation (PNP) and Standardised Precipitation Index (SPI), which were evaluated for various timescales (3, 6, 12, 24 and 48 months). Drought periods were identified using the drought indices and thresholds. The best-fit probability distributions between the Gamma, Weibull and Log-normal distributions were used for the calculation of the SPI and to develop SDF curves using frequency analysis. DDI and PNP do not quantify drought severity, making them unsuitable for developing SDF relationships. The developed SDF curves, based on the SPI, provide valuable tools for understanding drought dynamics and supporting decision-making in water resource management. This research highlights the importance of accessible data for prompt drought response to mitigate water shortages and economic losses in South Africa and suggests future research directions, including exploring alternative data sources and the impacts of climate change on droughts.