With few exceptions, human activities in the Sahara are totally dependent on the availability of water. Only in oases, where water is at or near the surface, can humans make a permanent home. Oases are scattered throughout much of the Sahara; many are situated along wadis and in the highlands, where rainfall is somewhat greater than in the rest of the desert. Some consist of small groves of palm trees, while others are large areas suitable for cultivation. Most of the Sahara's people live in oases and are engaged in agriculture. Dates, figs, and other fruits are the leading commercial crops. Wheat, barley, and a variety of vegetables are raised for local use. Crops are grown mainly by irrigation.
There are also many nomads who spend part of the year in the desert and the remainder either in the mountains or in an oasis. They live chiefly by herding sheep, goats, and camels, and by trading between oases and the cities on the desert fringe. Their number has been greatly reduced since the 1960's because of increasing aridity in and along the margins of the desert.