Desertification is devouring more than 20,000 square miles of land worldwide every year. In Africa , more than 2.4 million acres of land (73% of its drylands) are affected by desertification. Just 5,000 years ago the Sahara was covered with grasses and shrubs. Now it consists of basically two sub-climates, a dry subtropical climate in the north and a dry tropical climate in the south. The average rainfall in the subtropical region is approximately 3 inches (76 mm) per year. The temperatures in this kind of region can go below freezing at night and can go over 130 deg. F during the day.
Just like all other dessert climates the topographical features include shallow basins, large oasis depressions, serirs or regs (gravel-covered plains), plateaus, mountains, sand sheets and sand dunes.
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