Between desertification and re-greening of the Sahel region : diagnosis of remote sensing data and field observations
type: Dataset
description: The Sahel region is characterized by a strong bioclimatic gradient and is very sensitive to climatic fluctuations and especially to rainfall variability. Two successive and particularly severe droughts occurred in the 1970's and in the 1980's over the whole Sahel region, which had dramatic impact on the populations and their resources. The theory of a Sahel suffering from desertification was then refueled, as well as the view of a Sahara desert marching rapidly through the rest of the African continent. The analysis of the first remote sensing observations suitable for vegetation monitoring (available since the 1980's) proved to be at odds with these desertification assessments. Indeed, the satellite vegetation indices and particularly the NDVI evidenced strong positive trends, meaning that a significant increase in vegetation productivity occurred at the regional scale. This phenomenon was called "re-greening". However, no regional validation of such trends was possible due to the scarcity of field observations of vegetation. The objective of this work is to evaluate whether re-greening is actually happening over the Sahel or if some degradation trends of Sahelian ecosystems can be detected as well, using both field observations of vegetation and long-term NDVI data (GIMMS-3g NDVI). Within the framework of the AMMA-Catch observatory and of previous field programs, we now have almost 30 years of field observations in the Gourma region in Mali (1984-2011) and almost 20 years in the Fakara region in south-western Niger (1994-2011). The comparison of these two data sources (GIMMS-3g NDVI and vegetation productivity measured on the field) evidences strong re-greening patterns over the pastoral Gourma as well as an increase in vegetation productivity measured on the field. In contrast, the Fakara region in south-western Niger reveals decreasing trends for both variables. The consistency of satellite and field data confirms that NDVI can be used as a reliable tool for mon…
issued: 2026-05-07T00:20:30.493086
language: fr
modified: 2026-05-07T00:20:30.493091
contact point: Organization
  fn: CCSD
keyword: afrique
keyword: desertification
keyword: gimms-3g
keyword: infoeu-reposemanticsdoctoralthesis
keyword: modis
keyword: ndvi
keyword: physphysphys-geo-phphysics-physicsphysics-physicsgeophysics-physicsgeo-ph
keyword: productivite
keyword: reverdissement
keyword: rue
keyword: sahel
keyword: satellite
keyword: sdemcgenvironmental-sciencesglobal-changes
keyword: sdustugpsciences-of-the-universe-physicsearth-sciencesgeophysics-physicsgeo-ph
keyword: teledetection
keyword: theses
keyword: vegetation
landing page: https://theses.hal.science/tel-00944267

Between desertification and re-greening of the Sahel region : diagnosis of remote sensing data and field observations
type: Distribution
format: HTML
issued: 2026-05-07T00:20:30.514302
modified: 2026-05-07T00:20:30.465314
access URL: https://theses.hal.science/tel-00944267

test_moissonnage_selune
type: Agent