 In a longer term cycle, the gradual reduction in annual precipitation, coupled with a growing population, had begun a cycle in which increased use of arable land along the southern edge of the Sahara increased the rate of desertification, which in turn increased the use of the remaining arable land.Drought from the mid-1970s to early 1980s led to massive immigration from northern Darfur and Chad into the central farming belt.In 1983 and 1984, the rains failed.