ABSTRACT
ABSTRACT: The implementation of the UNCCD needs the identification of areas that record declining productivity of the vegetation over long-time periods. In this scope, we analyze the state of the vegetation productivity using 1982-1999 time series of NOAA-AVHRR NDVI data and compare it to rainfall data. For this, 354 rain gauges data distributed from yearly average isohyets 100 to 900 mm in five countries of West Africa are analyzed. We use for trends analysis, the ratio between integrated vegetation index (iNDVI) during the growing period (June to October) and the May to October sum of rainfall (RR). This ratio is a proxy of the Rain Use Efficiency is the widely accepted. Overall, 91% and 94% of RR and iNDVI data recorded positive trends over the 1982-1999 periods. Most stations in the Sahel were stable for the iNDVI/RR (49.5%). However, 37.8% showed strong to very strong negative change in the iNDVI/RR ratio, while only 1.3% showed positive trend. These strong negative trends recorded in more than 1/3 of the analyzed stations may reflect ongoing desertification processes in the Sahel and could be a starting point for the identification of hot-spots areas to determine where to take action within the National Action Programs (NAP) or Sub-Regional Action Programs (SRAP) to combat desertification.
