Changes in rainfall extremes over Southern Africa over the 20th and 21st centuries simulated by a high-resolution regional climate model and their connection to the Agulhas Current System

Abstract. In Southern Africa, precipitation is a crucial variable that is closely linked to agriculture and water supply. Additionally, extreme precipitation leads to devastating flooding, and heavy rainfall events pose a significant threat to the population in this region. Here, we analyse historical and scenario-based climate simulations, focusing on the spatial patterns of extreme precipitation and its projected future changes. We also investigate whether the Agulhas Current, a major regional oceanic current system, influences the frequency or intensity of extreme precipitation.

For this purpose, we analyse high-resolution simulations with the regional atmospheric model CCLM, conducted with a higher resolution (16 km x 16 km) than that normally used in the CORDEX project. One simulation is driven by meteorological reanalysis, whereas other simulations are driven by global coupled simulations that regionally resolve the Agulhas Current, its leakage and retroflection. The simulations cover the last few decades and the 21st century.

During the present period, the regional simulations indicate the strongest precipitation over Madagascar, the Mozambique Channel, and the adjacent mainland. Extreme rainfall events are most intense in Madagascar's mountainous regions, the Drakensberg, and the African Great Lakes. The extremes are generally stronger in the Summer Rainfall Zone than in the Winter Rainfall Zone. This climatological pattern agrees with available observations.

In the scenario simulation, extreme events are projected to intensify along the South African coast. In KwaZulu-Natal province, the heaviest future rainfall event is twice as strong as the strongest extreme simulated in the historical period and the recently observed disastrous extreme event in April 2022.

The simulations do not reveal a discernible impact of variations in the Agulhas Current System on strong rainfall events along the South African coast.