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The onset and cessation of seasonal rainfall over Africa

Dunning, C. M. ORCID:, Black, E. C. L. ORCID: and Allan, R. P. ORCID: (2016) The onset and cessation of seasonal rainfall over Africa. Journal of Geophysical Research: Atmospheres, 121 (19). pp. 11405-11424. ISSN 2169-8996

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To link to this item DOI: 10.1002/2016JD025428


Variation in the seasonal cycle of African rainfall is of key importance for agriculture. Here, an objective method of determining the timing of onset and cessation is, for the first time, extended to the whole of Africa. The method is applied to five observational datasets and the ERA-Interim reanalysis. Compatibility with known physical drivers of African rainfall, consistency with indigenous methods, and generally strong agreement between satellite-based rainfall datasets confirm the method is capturing the correct seasonal progression of African rainfall. The biannual rainfall regime is correctly identified over the coastal region of Ghana and the Ivory Coast. However, the ERA-Interim reanalysis exhibits timing biases over areas with two rainy seasons, and both ERA-Interim and the ARCv2 observational dataset exhibit some inconsistent deviations over West Africa. The method can be used to analyze both seasonal - interannual variability and long-term change. Over East Africa, we find that failure of the rains and subsequent humanitarian disaster is associated with shorter as well as weaker rainy seasons, e.g. on average the long rains were 11 days shorter in 2011. Cessation of the short rains over this region is 7 days later in El Niño and 5 days earlier in La Niña years with only a small change in onset date. The methodology described in this paper is applicable to multiple datasets and to large regions, including those that experience multiple rainy seasons. As such, it provides a means for investigating variability and change in the seasonal cycle over the whole of Africa.

Item Type:Article
Divisions:Interdisciplinary Research Centres (IDRCs) > Walker Institute
Science > School of Mathematical, Physical and Computational Sciences > National Centre for Earth Observation (NCEO)
Science > School of Mathematical, Physical and Computational Sciences > NCAS
Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:66825
Publisher:American Geophysical Union


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