a, Significant trends of woody cover (VOD) for 1992–2011, separated by the presence (**) or absence (×) of a significant (P < 0.05, n = 12,845) correlation with cumulative 2-year precipitation during this period. b, Changes in human populations for 1990–2010. The maps in a and b share a clear pattern: in particular, areas with a decrease in woody cover, and no relation to precipitation, coincide with a high population pressure. c, SAR model of the changes in woody cover, precipitation (both 1992–2011) and population (1990–2010). The units are expressed as change in the corresponding unit over the period of analysis.