Human-environment relationships in drylands, with a focus on the West African Sahel

The study of human-environment relationships in drylands, a topic that has engaged scientists for many decades, has captured new interest since satellite observations of land cover change over time became widely available. Particularly interpretations of the nature, extent and causation of desertification---or land degradation in drylands---have been influenced by the availability of more and more extensive time series of satellite observations.; This dissertation reviews some three decades of debate on the problem of desertification by examining advances in four disciplinary contexts in which these debates have evolved: our understanding of climate, ecology, social and political processes. Changes over time in these contexts have significantly influenced the direction of the desertification debate and created some controversy.; The respective roles that climate and human factors might have played in causing or sustaining environmental changes are then explored at the example of the West African Sahel region. Linear regression of time series of remotely sensed vegetation greenness data against rainfall data reveals where and to which extent trends in vegetation greenness are determined by rainfall, and, conversely, where other factors are likely to have played a significant role. While the results of the remote sensing study point to areas in which the impact of human factors is likely to have modified the simple rainfall-vegetation connection, claims of widespread human-induced desertification at a regional scale are challenged.