The Changing Climate of Africa Part III: Southern Africa

Most of South Africa’s climate is dominated by semi-permanent high pressure cells controlling the major upper-air circulation patterns. Through the combined effects of a stable relatively persistent South Atlantic anticyclone and the cold Benguela current, the west coast experiences arid conditions. While the South Atlantic high pressure cell exhibits small irregular longitudinal fluctuations, the South Indian oceanic anticyclone moves substantially eastward in summer and shifts westward towards the east coast in winter. These differences in stable anticyclonic control produce a decline in precipitation from east to west. Recent studies have established a strong correlation between rainfall anomalies in parts of the southern Africa summer rainfall zone since 1820 and extreme high and low phases of the Southern Oscillation. High phases of the latter, cold event summers, broadly correlate with above average rainfall; while low phases, warm event summers, are associated with drought in southern Africa. Dry as opposed to wet conditions over Southern Africa result from weakening of the tropical easterlies and strengthening of expansion equatorwards of westerlies.