On the Relative Impacts of Enso and Iodzm on Southern African Rainfall

An investigates the October to December rainfall variability over the mainland region of southeastern Africa in relation to El Nio Southern Oscillation (ENSO) and the Indian Ocean Dipole/Zonal Mode (IODZM) for the period 1950 to 1999 revealed that the north-south aligned areas of the eastern SADC are located in different co-variability regions. This meridionally aligned dipole rainfall anomaly configuration is captured only in the dominant principal component making it possible for the opposing rainfall anomalies of the two regions to have a common trigger. However, ENSO which has typically been invoked as the main cause for significant rainfall variability over this region cannot adequately explain this dipole rainfall anomaly pattern. The analyses strongly indicate that the positive IODZM phase events lead to a rainfall dipole such that floods occur over the north east of the region (around Tanzania) at the same time as droughts over the south east of the region (Zimbabwe, northern South Africa). Contrary to conventional knowledge, the ENSO association to this dipole rainfall anomaly pattern is not robust but appears to be the result of the well known ENSO-IODZM connection