Mise en évidence des zones touchées par la désertification par télédétection à basse résolution au Niger

Abstract

In order to identify areas where desertification may have occurred over the last two decades, 109 stations located in three bioclimatic zones of Niger are analyzed. Time series of remote sensing data are well suited to this task. Here, we use time series of NOAA AVHRR normalized difference vegetation index (NDVI) data and rainfall data. In this study, trend analysis is used to identify areas within the biomes from 1981 to 1999 in Niger with apparent land degradation in semi-arid areas. It appears that most of Niger (98%) recorded increasing rainfall while only 76% experienced increasing maximum NDVI. However, the combination of the two variables through the ratio shows a widespread reduction of the rain-use efficiency with non-significant trends for the stations located in northern Sahel (p=0.52), highly significant trends for those located in central Sahel (p=0.00009) and significant trends in southern Sahel (p=0.041). Overall, 75.3% of the sample recorded a significant reduction of the NDVIMax/RR ratio. Only one station out of four (24.7%) presented a stability of the ratio. These negative trends suggest a progressive diminution of the vegetation productivity as highlighted by the lowering of the NDVIMax/RR ratio. This situation suggests consistent environmental degradation and that desertification processes continued during the last two decades over most of the Sahelian belt of Niger.

Keywords

• desertification
• NDVI
• rainfall
• Sahel