The influence of ENSO on winter rainfall in South Africa

Authors

  • N. Philippon,

    Corresponding author
    1. Centre de Recherches de Climatologie, UMR5210 CNRS, Université de Bourgogne, Bâtiment Sciences Gabriel, 6 blvd Gabriel, 21000 Dijon, France
    • Centre de Recherches de Climatologie, UMR5210 CNRS, Université de Bourgogne, Bâtiment Sciences Gabriel, 6 blvd Gabriel, 21000 Dijon, France.
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  • M. Rouault,

    1. Department of Oceanography, Mare Institute, University of Cape Town, Rondebosch 7701, South Africa
    2. Nansen-Tutu Center for Environmental Research, University of Cape Town, Rondebosch 7701, South Africa
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  • Y. Richard,

    1. Centre de Recherches de Climatologie, UMR5210 CNRS, Université de Bourgogne, Bâtiment Sciences Gabriel, 6 blvd Gabriel, 21000 Dijon, France
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  • A. Favre

    1. Climate Systems Analysis Group, ENGEO department, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
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Abstract

Whereas the impact of ENSO on the African summer rainfall regions is largely documented and still regularly investigated, little is known about its impact on the winter rainfall regions located at the southwestern and northwestern tips of Africa. Yet, these regions are densely inhabited and are net exporters of high-quality agricultural products. Here we analyze the relationship between El Niño Southern Oscillation (ENSO) and South Africa austral winter rainfall using a 682 raingauges daily rainfall database documenting the period 1950–1999. The May, June and July (MJJ) seasonal rainfall amount shows a positive correlation with the Niño3.4 index that becomes significant since the so-called 1976/1977 climate regime shift. Wet spells properties (length, frequency and intensity) at the raingauge scale indicate that high (low) MJJ seasonal rainfall amounts recorded during El Niño (La Niña) events are the result of longer (shorter) wet spells in the Cape Town area and more (less) frequent wet spells north of 33°S. Wet spells with daily rainfall amounts ranging between 10 and 50 mm are also more (less) frequent. Atmospheric dynamics fields during wet spells feature lower (higher) pressure and northwesterly (southerly) wind anomalies in the troposphere over the region. This suggests that rain-bearing systems are deeper (thinner) and larger (smaller) in extent, and located farther north (south) during El Niño (La Niña) events. Copyright © 2011 Royal Meteorological Society

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