Identification of environmental anomaly hot spots in West Africa from time series of NDVI and rainfall

Studies of the impact of human activity on the vegetation dynamics in the Sahelian belt of Africa have been recently re-invigorated by new scientific findings that highlighted the primary role of climate in the drought crises of the 70-80s. Time series of satellite observations allowed identifying regreening of the Sahelian belt that indicate no noteworthy human effect on vegetation dynamics at sub continental scale from 80s to late 90s. However, several regional/local crises related to natural resources occurred in the last decades despite the re-greening thus underlying that more detailed studies are needed. This study contributes to the understanding of climate and human impacts on the vegetation in the Sahelian region in the last decade (1998-2010). The use of time-series of SPOT-VGT NDVI and FEWS-RFE rainfall estimates allowed us to analyze vegetation and rainfall trends and to identify local anomalous situations. Trend analysis has been conducted to map a) areas where vegetation has been significantly decreasing or increasing due to changes in rainfall patterns and b) anomalous hot spot zones where vegetation dynamics could not be fully explained by changes of rainfall patterns. Multi-temporal analysis of Landsat images allows us to evaluate the reliability of the identified trends and to provide an interpretation of some example hot spots. The frequency distribution of the anomalous situations among the land cover class of the GlobCover map shows that, at the regional scale, environmental degradation occurs mainly in herbaceous vegetation covers where pastoral and cropping practices are often critical due to low and very unpredictable rainfall. The results of this study show that even if a general positive re-greening trend due to increased rainfall is evident for the entire Sahel, some local anomalous hot spots exist and can be explained by human factors such as population growth whose level reaches the ecosystem carrying capacity as well as population displacement leading to vegetation recovery.

BOSCHETTI Mirco;  NUTINI Francesco;  BARTHOLOME Etienne;  HOSCILO Agata;  STROPPIANA D.;  BRIVIO Pietro Alessandro; 

2013-02-25

ELSEVIER SCIENCE BV

JRC65577

0924-2716,   

http://www.sciencedirect.com/science/article/pii/S0924271613000099,    https://publications.jrc.ec.europa.eu/repository/handle/JRC65577,   

10.1016/j.isprsjprs.2013.01.003,