The influence of ENSO on South Africa winter rainfall

Nathalie Philippon (1) , Mathieu Rouault (2) , Yves Richard (1) , Alice Favre (3)

1 CRC - Centre de Recherches de Climatologie
2 Department of Oceanography [Cape Town]
3 CSAG - Climate Systems Analysis Group [Cape Town]

We analysed 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 mid 70's. 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 and larger (thinner and smaller), and located further north (south) during El Niño (La Niña) events.

Mots clés: winter rainfall; western South Africa; ENSO; intra-seasonal variability; wet spells

Domaines: Climatologie; Milieux et Changements globaux

Nathalie Philippon, Mathieu Rouault, Yves Richard, Alice Favre. The influence of ENSO on South Africa winter rainfall. International Journal of Climatology, 2011, pp.DOI: 10.1002/joc.3403. ⟨hal-00552940⟩