Future trends in atmospheric circulation patterns over Africa south of the equator

Abstract

The impact of climate change on the frequency of occurrence of atmospheric circulation patterns can have a wide range of consequences ranging from weather extremes to the modification of pollutant transport. This study uses 11 CMIP6 global climate models (GCMs) to investigate the impact of future climate change on the frequency of occurrence of atmospheric circulation patterns, in Africa south of the equator. Here it is shown from the historical analysis that there are statistically significant trends in the frequency of occurrence of some of the classified circulation types (CTs) in the study region. Further, under the SSP5-8.5 and SSP2-4.5 emission scenarios, the historical CTs were reproduced, suggesting that future climate change will not constrain the existence of the CTs. However, for future emission scenarios, the ensemble of the GCMs projects notable changes in the spatial structure of the CTs and statistically significant trends in the frequency of occurrence of most of the CTs, towards the end of the 21st century. The intensity of the projected changes in the spatial structure and linear trends in the frequency of occurrence of the CTs are relatively stronger under the higher emission scenario. As regards changes in synoptic circulations in the study region, the ensemble of the GCMs project, (i) a positive trend in the frequency of occurrence of austral summer dominant CTs associated with atmospheric blocking of the Southern Hemisphere mid-latitude cyclones, adjacent to South Africa; (ii) alternating frequent periods of enhanced (suppressed) anticyclonic circulation at the western branch of the Mascarene high possibly due to a more positive phase of the Southern Annular Mode (warmer southwest Indian Ocean); (iii) possible weakening of the Angola low. The aforementioned changes can be expected to have direct impacts on the regional climates in the study region. HIGHLIGHTS The obliquely rotated principal component analysis, applied in a fuzzy approach, is used to classify atmospheric circulation patterns using reanalysis data, and GCM data sets under the historical experiment and 2 future emission scenarios.; The individual GCMs faithfully simulate the circulation patterns as obtained from ERA5 reanalysis.; The climate models project an increase in the intensity and frequency of occurrence of atmospheric blocking, adjacent to southern Africa.; Climate models project an increase in the frequency of occurrence of two distinct summer circulation types, with one associated with stronger circulation and the other associated with weaker circulation at the western branch of the Mascarene high.;

Keywords

• africa south of the equator
• atmospheric circulation
• climate change
• emission scenarios
• indian ocean
• mascarene high