From El Niño to La Niña: Vegetation Response Patterns over East and Southern Africa during the 1997–2000 Period

During the period 1997–2000, the global climate system experienced a transition from the strongest ENSO warm event this century in 1997/98 to a strong cold event in 1999/2000. Normalized difference vegetation index (NDVI) time series data derived from the Advanced Very High Resolution Radiometer (AVHRR) instrument aboard the NOAA polar-orbiting satellite series were analyzed to resolve the land surface response patterns over Africa during this period. The rearrangement of precipitation patterns induced by the change from El Niño to La Niña conditions had significant effects on biomass production in arid and semiarid lands of Africa as revealed by NDVI anomaly patterns, particularly in equatorial East Africa and southern Africa where the ENSO–precipitation linkage is most pronounced. In general, there was a reversal in NDVI response patterns in East (southern) Africa from positive (negative) during the El Niño in 1997/98 to negative (positive) during the La Niña event in 1999/2000. These changes can partially be attributed to east–west reversal in SST gradients in the Pacific Ocean basin but more significantly to the changes in the SST anomaly patterns in the equatorial western Indian Ocean (WIO) off the East African coast and the southern Indian Ocean off the southern African coast.