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

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posted on 2023-06-09, 12:52 authored by R C Blamey, Seshu Kolusu, P Mahalela, Martin ToddMartin Todd, C J C Reason
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.

Funding

GROFUTURES: Groundwater Futures in Sub-Saharan Africa; G1702; NERC-NATURAL ENVIRONMENT RESEARCH COUNCIL; NE/M008207/1

DRiSL: The Drought Risk Finance Science Laboratory; G2314; NERC-NATURAL ENVIRONMENT RESEARCH COUNCIL; NE/R014272/1

Uncertainty reduction in Models For Understanding deveLopment Applications (UMFULA); G1671; NERC-NATURAL ENVIRONMENT RESEARCH COUNCIL; NE/M020258/1

Towards Forecast-based Preparedness Action (ForPAc): Probabilistic forecasts information for defensible preparedness decision-making and action; G2043; NERC-NATURAL ENVIRONMENT RESEARCH COUNCIL; NE/P000673/1

History

Publication status

  • Published

File Version

  • Accepted version

Journal

International Journal of Climatology

ISSN

1097-0088

Publisher

Royal Meteorological Society

Issue

11

Volume

38

Page range

4276-4295

Department affiliated with

  • Geography Publications

Research groups affiliated with

  • Sussex Sustainability Research Programme Publications

Full text available

  • Yes

Peer reviewed?

  • Yes

Legacy Posted Date

2018-04-16

First Open Access (FOA) Date

2019-07-13

First Compliant Deposit (FCD) Date

2018-04-16

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