Question 1: Desertification in Niger, the Sahel Figure 1 is a resource-booklet figure showing annual rainfall at Tahoua, Niger. The Sahel is a fragile semi-...

(a) Any two valid physical factors: naturally thin or nutrient-poor soils; high temperatures causing high evaporation; strong dry-season winds that remove exposed topsoil; sparse natural vegetation; occasional intense rainstorms that cause runoff and erosion. (b) For example, overgrazing by cattle, goats or sheep removes plant cover; bare soil is then exposed to erosion. Fuelwood collection or clearing land for cultivation are also valid activities if linked to loss of vegetation. (c) Rainfall fell from 350 mm in 1980 to 280 mm in 1990; it fell further to a low of 240 mm in 2000; rainfall then rose to 300 mm by 2010; however, 2010 rainfall was still 50 mm below the 1980 value. (d) Prolonged low or unreliable rainfall reduces plant growth and can kill grasses, shrubs and crops. With less vegetation, roots no longer bind the soil and there is less leaf cover to protect it. A growing population may cultivate marginal land, keep too many livestock, or cut trees for fuel. These activities remove vegetation faster than it can regenerate, especially during drought. The exposed soil is baked hard by high temperatures, so rainfall infiltrates less easily. When intense rain does fall, it runs over the surface, washing away fertile topsoil; wind can also blow away dry fine material. Soil moisture, organic matter and fertility decline, crop yields fall, and farmers may clear or graze even more land. This positive feedback can turn productive semi-arid land into degraded desert-like land: desertification.