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Extreme rainfall occurred over the South African east coast during 10–12 April 2022, leading to over 500 deaths and massive damage. This study seeks to understand a key feature, namely the progression of the rainfall maxima from the northern KwaZulu-Natal (KZN) coast during the night of 10–11 April by ~550 km to the Eastern Cape coast about 48 h later. The large-scale circulation was dominated by a cut-off low over the South African interior with a strong ridging anticyclone southeast of the country in the South Indian Ocean. Satellite, rain gauge, and ERA5 reanalysis are used to show that the timing and location of the heaviest rainfall are closely tied to, firstly, the formation of a Mesoscale Convective System (MCS) at ~0300UTC April 11 on the northern KZN coast which tracked south and then offshore, and secondly, a meso-trough which formed a coastal meso-low by ~2100 UTC April 11. The meso-low tracked south over the warm waters of the Agulhas Current before strengthening into Subtropical Depression Issa. Mesoscale interaction between the MCS and coastal meso-low determined the positioning and timing of the strongest onshore low-level jet, moisture convergence and uplift, and hence the progression of the heavy rainfall down the coast. Such mesoscale interaction has not previously been documented in southern Africa or the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

The Okavango River Basin (ORB) is a highly sensitive and biodiverse region in southern Africa whose climate, vegetation and river discharge characteristics are not well understood. This study investigated relationships between rainfall, temperature, Normalized Difference Vegetation Index (NDVI) and river discharge over the region as well as their trends and interannual variability. It is found that spatial patterns of NDVI are closely related to those of rainfall, but less so with temperature at monthly and seasonal time scales. The relationships between NDVI and rainfall/temperature differ north of 18.9°S where rainfall is higher than to its south. Typically, there are lags of 1–2‐months between NDVI and either rainfall or temperature. Also, there are large areas across the region that show significant warming trends in all seasons as well as wetting (mainly in the north). This increasing trend in surface temperature may act to worsen the impacts of extreme events such as severe drought and fire in the region. There is also pronounced interannual variability with significant correlations found with El Niño‐Southern Oscillation (ENSO), the subtropical South Indian Ocean Dipole and the Botswana High for rainfall and temperature, and for NDVI with ENSO. For the Southern Annular Mode, significant correlations were found with rainfall and temperature only in December and April. On longer time scales, focus was also placed on the wet 2006–2013 period relative to much drier 1999–2005 epoch for October–December. The wetter conditions during 2006–2013 appear related to La Niña Modoki conditions and warmer sea surface temperature near Angola as well as regional circulation differences. [ABSTRACT FROM AUTHOR]

There are at least two types of ridging South Atlantic Ocean high pressure systems in the South African domain. Type-N events occur north of 40°S and Type-S occur south of this latitude line. This study shows that there is no evidence of surface downstream development in terms of the evolution of eddy kinetic energy and associated ageostrophic geopotential fluxes for both types of ridging high events. Rather, for these systems downstream development is an upper level process. The baroclinic waves associated with the ridging develop from baroclinic instability, by converting eddy available potential energy to eddy kinetic energy. The bulk of the conversion is located at the upstream end of the waves. The downstream trough, which is the part of the wave that influences upward motion over South Africa, develops from the transport of eddy kinetic energy across the trough axis by means of ageostrophic geopotential fluxes. These fluxes are stronger for Type-S events. The absence of downstream development at the surface and the presence of it aloft demonstrates that there are differences in the underlying dynamics in the evolutions of these systems in the vertical. The evolution of eddy kinetic energy associated with baroclinic waves that occur during the ridging events is different from what has been observed for cut-off low pressure systems in the South African domain. [ABSTRACT FROM AUTHOR]