Distinguishing southern Africa precipitation response by strength of El Niño events and implications for decision-making
December–February precipitation in southern Africa during recent El Nino events is studied by distinguishing circulation and precipitation responses during strong and moderate-to-weak events. We find that while both strong and moderate-to-weak El Nino events tend to dry southern Africa, the pattern and magnitude of precipitation anomalies in the region are different, with strong El Nino events resulting in rainfall deficits often less than −0.88 standardized units and deficits of only about half that for the moderate-to-weak case. Additionally, the likelihood of southern Africa receiving less than climatologic precipitation is approximately 80% for strong El Nino events compared to just over 60% for moderate-to-weak El Nino. Strong El Nino events are found to substantially disrupt onshore moisture transports from the Indian Ocean and increase geopotential heights within the Angola Low. Since El Nino is the most predictable component of the climate system that influences southern Africa precipitation, the information provided by this assessment of the likelihood of dry conditions can serve to benefit early warning systems.