The Sahara desert is the world’s largest desert, covering over 3,500,000 square miles of Northern Africa. It is actually the size of the United States. Africa is divided into North and Sub-Saharan Africa by the Sahara desert. A band of semiarid savanna called the Shael marks the southern border of the Sahara. South of the Sahel lies the lusher Sudan adn the Congo River Basin. The Sahara mostly consists of rocky hamada, which is a type of desert landscape consisting of largely barren, hard, rocky plateaus, with very little sand.
Thousands of years ago the Sahara was much wetter than it is today. Other than in the Nile Valley where there are a few oases or isolated areas of vegetation in a desert, and in the northern highlands where plants such as olive trees are found to grow, modern day Sahara is not lush in vegetation. Currently, over 2.5 million people live in the Shara. Most in Egypt, Mauritania, Morocco, and Algeria. The dominant ethnicities in the Sahara desert are Berber groups, Arabised Berber groups, and black African ethnicities.
Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan, and Tunisia covers the huge parts of the Sahara. It is once of the three distinct physiographic provinces of the African massive physiographic division.Desert landforms like sand dunes, stone plateaus, gravel plains, dry valleys, salt flats and dune fields of the Sahara are shaped by the wind or sometimes the very occasional rains. There are several deeply dissected mountains, mostly volcanic, that rise from this desert. The highest peak in the Sahara is Emi Koussi, a shield volcano in Northern Chad. Most River and streams in the Sahara are intermittent, with the big exception of the Nile river, of course, which crosses the desert and empties into the Mediterranean. The central part of the Sahara is hyper-arid, with little vegetation. The northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in wadis where moisture collects.
The Sahara climate has undergone huge variations between wet and dry over the last few thousands of years. The Sahara desert was even bigger than it is today during the last glacial period. It extended even more south than it does today. Once all the ice was gone the Sahara dried out, but the drying trend was soon counteracted by the monsoon, which brought rain further north than it does today. Monsoons are due to heating of air over the land during summer. The hot air rises and pull in cool wet air from the ocean, thus causing it to rain. The Sahara was actually wetter when it received more solar insulation in the summer.
Recently, signals are indicating that the Sahara and its surrounding regions are greening due to increase rainfall. Satellites show extensive greening of the Sahel between 1982 and 2002 and in the east and west of the Sahara.