12.5
The relationship between southern Africa Rainfall and ENSO events
Washington Zhakata, University of Witwatersrand, Johannesburg, South Africa
This paper examines the annual rainfall over southern Africa during 11 ENSO events within the period 1950 to 1995. During four of these, unusually wet conditions prevailed in some parts of southern Africa whilst the rest of the subcontinent received normal rains. The other seven events were characterised by below normal rainfall. A comparison of the interannual rainfall variations with ENSO, based on sea surface temperature patterns in the Pacific, shows an excellent correspondence. An ENSO classification scheme of Fu et al., also showed good comparison with the southern Africa rainfall anomalies during the ENSO events. Type 1 years, with large positive temperature anomalies east of the date line and lasting well into winter, are invariably events that inhibit southern Africa rainfall, causing serious rainfall deficits. Normal years coincide with type 3 year, with weak anomalies confined to the eastern Pacific, whilst type 2 ENSO events, which are characterised by moderate warming over a broad sector may also be associated with below normal rainfall, but not drought conditions.
This study also shows that the response to ENSO is regionally specific. Although throughout southern Africa most years with extremely wet conditions are non-ENSO years, the tendency for an ENSO event to decrease rainfall is greatest in central southern Africa, where 7 of 11 events produced well below normal rainfall. The wettest years are generally associated with the cooling of the eastern Pacific waters. The pattern is more complex in coastal areas where the ENSO signal is very weak. The reasons for the geographical pattern of response become apparent when the seasonality and causes of rainfall in the various regions are evaluated.
Session 12, Regional Issues: Africa
Wednesday, 26 March 2003, 1:30 PM-5:15 PM
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