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date: 20 September 2017

Climate of Southern Africa

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Climate Science. Please check back later for the full article.

Southern Africa extends from the equator to about 34oS and is essentially a narrow peninsula-like landmass surrounded on three sides by oceans. Its termination in the mid-ocean subtropics has important consequences for regional climate, since it allows the strongest western boundary current in the world ocean (warm Agulhas Current) to be in close proximity to an intense eastern boundary upwelling current (cold Benguela Current). Unlike other western boundary currents, the Agulhas retroflects south of the landmass and flows back into the South Indian Ocean, thereby leading to a large area of anomalously warm water south of South Africa that may influence storm development. Two other rather unique regional ocean features imprint on the climate of southern Africa—the Angola-Benguela Frontal Zone (ABFZ) and the Seychelles-Chagos thermocline ridge (SCTR). The former is important for the development of Benguela Niños and flood events over southwestern Africa, while the SCTR influences Madden-Julian oscillation and tropical cyclone activity in the western Indian Ocean.

In addition to Benguela Niños, southern African climate is strongly impacted by El Niño Southern Oscillation (ENSO) and to a lesser extent the Southern Annular Mode (SAM) and sea surface temperature (SST) dipole events in the Indian and South Atlantic Oceans. The regional land-sea distribution leads to a highly variable climate, on a range of scales, which is still not well understood due to its complexity and its sensitivity to a number of different drivers. Strong and variable gradients exist not only in the neighboring oceans, but also in several aspects of the landmass, and these all influence the regional climate and its interactions with climate modes of variability.

Much of the interior of southern Africa consists of a plateau, on the order of 1–1.5 km high, and a narrow coastal belt that is particularly mountainous in South Africa, leading to sharp topographic gradients. This topography is able to influence the track and development of many weather systems, leading to marked gradients in rainfall and vegetation across southern Africa. The presence of the large island of Madagascar, itself a region of strong topographic and rainfall gradients, has consequences for the climate of the mainland by reducing the impact of the moist trade winds on the Mozambican coast and the likelihood of tropical cyclone landfall there. It is also likely that at least some of the relativity aridity of the Limpopo region in northern South Africa and southern Zimbabwe results from the location of Madagascar in the southwestern Indian Ocean.

While leading to challenges in understanding its climate variability and change, the complex geography of southern Africa offers a very useful test bed for improving the global models used in many institutions for climate prediction. Thus, research into the relative shortcomings of these models in the southern African region may lead not only to better understanding of southern African climate, but also to enhanced capability to predict it globally.