Extreme rainfall events in southeastern Africa during the summer

The Pongola-Mtamvuna (PM) water management area in southeastern Africa is a highly biodiverse and sensitive region whose rainfall variability is not well understood. It is prone to drought and the occasional devastating flood events which are studied here for the early (October–December) and late summer rainy seasons (January–March) from 1984 to 2019 using CHIRPS daily rainfall data. Over 60% of the top 50 extreme rainfall events occurred during late summer (January–March) with tropical lows being by far the main contributor. The remainder are more or less equally distributed between mesoscale convective systems, tropical-extratropical cloud bands and cut-off lows, the latter contribute in October and November. There is considerable interannual variability in the numbers of these events during the record some of which is related to ENSO. Two prominent exceptions are the wet El Niño of OND 2006 and the dry La Niña of OND 2011, SST anomalies in the greater Agulhas Current region seem to have played an important role in both cases. Far fewer extreme events occurred from 2002 onwards than in the first two decades. However, 7 of the top 50 events occurred during the multi-year drought of 2007–2018 when almost all the late summers as well as many of the early summers experienced below average rainfall. The dry conditions during this period would have been much worse had 7 of the top 50 extreme events not occurred then, highlighting the importance of extreme rainfall event analysis for the region.