Arid and Semi-arid Environments of the World

Abstract

More than one third of the earth’s land surface (ca. 49 million km²) is arid or semi-arid, receiving less than 400 mm annual precipitation, supporting more than 1.2 billion people, or 20% of the world’s population, a population that is now expanding at a far greater rate than the environment can support. The pressure on the land is such that 50 000–70 000 km² of useful productive land is being lost each year through desertification. Furthermore, an estimated 3.8 million km² of the arid and semi-arid lands is also saline; in the Indian subcontinent alone some 400 km² are lost annually to agriculture due to increasing salinity, while in the USA, with its far more sophisticated agriculture, the area lost is 800–1200 km² (Bell 1985; Wickens 1992). The world’s arid lands, the true deserts and the desert margins, are not only hostile to life, but also endangered.