The 1950-1998 warm ENSO events and regional implications to river flow variability in Southern Africa

Abstract

The variability of annual river runoff and its possible association with the 1950-1998 seasonal El Niño/Southern Oscillation (ENSO) is investigated in 502 rivers gauged in 9 countries of the Southern African region. We found some evidence of possible links between available surface water resources in terms of mean annual runoff and warm ENSO events. This was revealed by the existence of strong and nearly-strong positive linear correlation between annual discharges and the warm seasonal ENSO indices explained by the sea level pressure (SLP) data. Of the 502 rivers we considered, 150 rivers exhibit strong positive correlation
between the December to February quarter ENSO indices and the annual runoff – with 25% of the variance in annual runoff being accounted for by the warm ENSO events. A relatively weaker positive correlation also occurred in 174 rivers we
considered. The strong positive correlation occurs in parts of Zambia, Namibia, Mozambique and the lowveld in South Africa. In these parts of Southern Africa, there is evidence of a general decline in annual runoff after the mid-1970s compared to the period before it. These revelations are explored and are found to be partly explained by the high frequency of drought-related warm ENSO phenomena that occurred during the same period.

Water SA Vol.32 (4) 2006: pp.459-463