The trends in heatwaves and associated synoptic conditions across the upper Limpopo Basin of Botswana and South Africa

This paper evaluates the interannual variability and trends in heat extremes across the Limpopo River Basin in Southern Africa, with a specific focus on heatwaves and their associated synoptic conditions. Extreme weather events pose a considerable threat to livelihood, health, agriculture, and economy due to their severe impacts. The purpose of this research is to strengthen the understanding of heatwaves' trends and their associated synoptic states in a highly climate-vulnerable region of Southern Africa. This should help inform scientists, decision-makers, and stakeholders about the risks of heatwaves and raise public health awareness. In the analysis of heat extremes, a statistical tool called RClimDex developed by the Expert Team on Climate Change Detection and Indices performed a statistical analysis of climate indices at individual stations. RClimDex tool enabled for the definition, detection, and analysis of heat extremes in a standardized way, making it possible to compare results of various places and obtain coherent climate trends. Thereafter, the Self-organising Maps methodology was employed to investigate and visualize the synoptic systems associated with the observed regional heatwaves during austral summer. The trend analysis of heat extremes revealed a warming local climate, with increases in the duration of heatwaves and increases in the percentage number of extreme hot days and nights. It was detected that heatwaves were characterised mostly by a dominant and blocking South Indian high-pressure system co-existing with a mid-latitude cyclone. Single-occurring high-pressure systems such as the South Indian High or South Atlantic High were also found to be characteristic of heatwaves. Interestingly, the associated synoptic systems’ interannual trends were not corresponding to the observed increases in the duration of heatwaves, and this finding directs areas of further research to understand other contributing factors to the observed trends in heatwaves.