Sensitivity of Vegetation (Ndvi) to Climate Over Southern Africa: Relationships With Summer Rainfall and Olr

Relationships between satellite normalised difference vegetation index (NDVI) and outgoing longwave radiation (OLR) data are studied over southern Africa. Analysis of the seasonal cycle confirms an inverse relationship, whereby reduced OLR in summer resulting from increased clouds and rainfall contributes to an increase in the vegetative density and cover. Field-to-field correlations between OLR and NDVI in the period 1982–1993 are significantly negative in late summer (January-April) in a N-S axis south of 20°S. The weather Regimes of early summer, made up of continental troughs, appear less able to influence vegetation than those in the late summer dominated by an anticyclone to the east. Positive (inverted) correlations between OLR and NDVI occur in the 10–15°S ITCZ Region where annual rainfall is > 1 m. Interannual variability of OLR and NDVI are associated with the El Nino Southern Oscillation (ENSO) cycle, driven by warming of the tropical Atlantic and Indian Oceans. Principal components analysis identifies a large area of sympathetic response over the central plateau of southern Africa in OLR, and NDVI. a gridded summer rainfall time series from 1905 exhibits a nearly identical spatial loading pattern, and gives added meaning to satellite results in the 1982–1993 period.