Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 3 2009 10.5194/bg-6-469-2009 http://www.biogeosciences.net/6/469/2009/ http://www.biogeosciences.net/6/469/2009/bg-6-469-2009.html http://www.biogeosciences.net/6/469/2009/bg-6-469-2009.pdf 469 477 2009-03-26 Disentangling the effects of climate and people on Sahel vegetation dynamics J. W. Seaquist jonathan.seaquist@nateko.lu.se T. Hickler L. Eklundh J. Ardö B. W. Heumann Department of Physical Geography and Ecosystems Analysis, Geobiosphere Science Centre, Lund University, Sölvegatan 12, 223 62, Lund, Sweden Department of Geography, University of North Carolina at Chapel Hill, Saunders Hall, Campus Box 3220, Chapel Hill, NC 27599-3220, USA The Sahel belt of Africa has been the focus of intensive scientific research since the 1960s, spurred on by the chronic vulnerability of its population to recurring drought and the threat of long-term land degradation. But satellite sensors have recently shown that much of the region has experienced significant increases in photosynthetic activity since the early 1980s, thus re-energizing long-standing debates about the role that people play in shaping land surface status, and thus climate at regional scales. In this paper, we test the hypothesis that people have had a measurable impact on vegetation dynamics in the Sahel for the period 1982–2002. We compare potential natural vegetation dynamics predicted by a process-based ecosystem model with satellite-derived greenness observations, and map the agreement between the two across a geographic grid at a spatial resolution of 0.5°. As aggregated data-model agreement is very good, any local differences between the two could be due to human impact. We then relate this agreement metric to state-of-the-art data sets on demographics, pasture, and cropping. 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