Mise en évidence de la résilience de la végétation sahélienne par télédétection basse résolution au Niger à la suite d’épisodes de sécheresse

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 (82,5%) recorded increasing rainfall while only 78,9% experienced increasing in integrated vegetation index (iNDVI). However, the combination of the two variables through the ratio iNDVI/RR shows a widespread reduction of the rain-use efficiency with highly significant trend for the stations grouped by bioclimatic area (p<10-6) during the studied period (1981-1999). These negative trends suggest a progressive diminution of the vegetation productivity as highlighted by the lowering of the iNDVI/RR ratio. This situation suggested a consistently environmental degradation and that desertification processes continued during the last two decades over most of the Sahelian belt of Niger.

Keywords

• iNDVI
• rainfall
• desertification
• Niger
• Sahel