The role of regional circulation features in regulating El Niño climate impacts over southern Africa: a comparison of the 2015/16 drought with previous events

Blamey, Ross, Kolusu, Seshagirirao, Mahalela, P, Todd, Martin and Reason, Chris (2018) The role of regional circulation features in regulating El Niño climate impacts over southern Africa: a comparison of the 2015/16 drought with previous events. International Journal of Climatology. ISSN 1097-0088 (Accepted)

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Abstract

Extremely dry conditions were experienced across most of southern Africa during the austral summer (October-March) of 2015/16, associated with one of the strongest observed El Niño events in the Pacific. Dry conditions peaked in the early austral summer months (October-December) producing the most intense drought in the 116 year historical record, as measured by the intensity of the Standardized Precipitation Index across all spatial scales up to the sub-continental. We estimate the return period of this extreme early summer drought to be greater than 200 years. The interior and eastern parts of South Africa were particularly hard-hit with station data showing rainfall totals being at their lowest since at least 1950. The early summer dry conditions make the 2015/16 event atypical compared to past El Niño events of similar magnitude. We find that key regional circulation patterns, influenced by planetary scale processes, play an important role in modulating the spatial and temporal evolution of the summer rainfall during these El Niño events. Specifically, (i) the Angola Low and the South Indian Ocean High, two dominant low level circulation features that drive moisture convergence to support convective precipitation in the region, were anomalously weakened in early austral summer of 2015/16 resulting in less moisture being transported over the continent, and (ii) the mid-level Botswana High was stronger than in previous El Niño years further producing unfavourable conditions for rainfall through stronger subsidence in the mid- to upper levels over southern Africa.

Item Type: Article
Keywords: Droughts, southern Africa, El Niño, Angola Low, Botswana High, tropical- extratropical connections
Schools and Departments: School of Global Studies > Geography
Research Centres and Groups: Sussex Sustainability Research Programme
Depositing User: Martin Todd
Date Deposited: 16 Apr 2018 15:13
Last Modified: 16 Apr 2018 15:13
URI: http://sro.sussex.ac.uk/id/eprint/75135

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