Yasir E. Mohieldeen^1,, Mohammed Mahgoub Hassan²

Numerous studies have established a link between the Normalized Difference Vegetation Index (NDVI) and rainfall. However, the influence of different ecological zones on this relationship over large regions has often been underestimated. In this study, correlation analyses conducted in Sudan and Southern Sudan indicated that, although NDVI and rainfall demonstrate a strong positive annual correlation, NDVI values during dry years are unexpectedly higher than those recorded in wet or normal years for equivalent rainfall amounts. Several researchers have suggested that such findings may be due to a lag between precipitation events and vegetation response. The present study’s analysis of growing seasons further substantiated these seemingly contradictory patterns between rainfall and NDVI dynamics. To clarify these contrasts, we examined seasonal rainfall distribution in conjunction with major ecological zones. The results demonstrated that the north-south movement of the rainfall front between dry and wet years within the Sudano-Sahelian region, which encompasses diverse ecological zones, produces season-specific NDVI-rainfall relationships. Specifically, in dry years, rainfall events tend to shift southward into areas dominated by perennial vegetation types such as woodlands and thickets, where high NDVI values are typical. Conversely, in wet years, rainfall expands northward into semi-desert grasslands, which are characterized by low water use efficiency and correspondingly low NDVI values.

NDVI-Rainfall dynamics, growing season, ecological zonation, Arid & Semi-arid ecosystems, NOAA AVHRR