Identifying trends in extreme hydro-meteorological events to assess water-related hazards in urban-rural areas in South Africa

Building resilience in urban-rural areas against hydro-meteorological hazards such as prolonged droughts and floods is crucial for economic development and safeguarding vulnerable people in Africa. Extreme hydro-meteorological events are projected to become more frequent and intense under climate change, leading to human, material, economic and environmental losses and impacts. In particular, southern Africa exhibits pronounced hydro-meteorological extreme events in response to El Niño and La Niña events, with El Niño Southern Oscillation (ENSO) impacts projected to intensify in southern Africa in a warmer world. Two of South Africa’s major river systems have been identified as hot spots of water-related hazards, in the context of major risks of water insecurity and flood disasters in a warmer world.

The Integrated Vaal River System (IVRS), a large, complex water system comprising water resources of different river basins, and several mega-dams within, serves as a water lifeline of the Gauteng Province, the economic hub in South Africa. The IVRS is vulnerable to the occurrence of multi-year droughts. Although a drought so severe that the IVRS can no longer supply the Gauteng Province with water (a ‘day-zero drought’) has never occurred before in the historical record, a four-year drought culminating in the El Niño drought of 2015/2016 resulted in the level of the Vaal Dam falling to about 25% (a dam level below 20% would have implied the presence of a day-zero drought). East of the Lesotho highlands, major rivers such as the Umgeni drain eastwards towards the KwaZulu-Natal coastal plain. These rivers are prone to flooding, especially during La Niña years. In April 2022, South Africa experienced its worst flood disaster when more than 544 people died during flash flooding in the Umgeni, Mlazi and Mbokodweni rivers in the greater Durban area. Present analysis focuses on changes in trends and characteristics of drought and extreme precipitation events in both study regions for the past 40-years using the ERA5-Land reanalysis and observational datasets such as CHIRPS. The ERA5-Land dataset has a spatial resolution of 0.1°x0.1° (~11 km) and goes back to 1950, making it possible to analyse long-term trends of meteorological drought and extreme precipitation. Results will highlight changes in frequency, duration and intensity of hydro-meteorological extreme events.

The research is part of the “Water security in Africa – WASA” programme, project WaRisCo, which deals with water risks and resilience in urban-rural areas in southern Africa and the co-production of hydro-climate services for an adaptive and sustainable disaster risk management.