Detection of recent changes in Gambia vegetation cover using time series modis ndvi

Abstract

In The Gambia, the vegetation cover has undergone significant changes over the past two decades. To assist policy decision-making, this study seeks to detect trends in changes over the past two decades using a time series of NDVI MODIS images. The methodological approach is based on the calculation of the correlation of Kendall (τ) associated with the p-significance test at the 10 % threshold. The results showed a trend of increasing vegetation productivity during the decade 2000-2009 (98.37% of the study area) in almost all administrative regions. This trend is more significant along the river. In contrast, during the decade 2010-2019, it was noted overall significant downward trend in productivity (44.01% of The Gambia) in all administrative regions except West Coast Region and Banjul, however not significant. The result showed that, over the whole period (2000-2019), 61.86% of the national territory was characterized by a positive trend and 38.14% by a negative trend; and that the significant positive trend percentage is 10%, the significant negative trend percentage is 4%. Significant positive trends are observed much more along the river and central of the Central River Region; significant negative trends are observed mainly in the western part of West Coast Region and Banjul, at the eastern end of the North Bank Region and in the Upper River Region.