The Sahelian zone borders the southern Sahara. Vegetation—scattered grasses, shrubs, and trees—increases in density towards the southern margin. Annual rainfall is 200–400 mm, but unreliable. Severe droughts bring losses of livestock, crop failures, and famine. See Glob. Env. Change (2001) 11, 1, special Sahel issue. The work by D. Hummel, M. Doevenspeck, and S. Samimi (2001) micle (Migration, Climate & Environment) working paper #1 is a superb resource on climate change, environment, and migration in the Sahel.