1. Geographic Extent and Characteristics of the World’s Arid Zones and Their Peoples

Arid lands are a vital part of the earth’s human and physical environments. Human population is thin except in Indian arid zone, which is one of the most densely populated arid zones of the world. Arid land ecosystems play a major role in global biophysical processes by reflecting and absorbing solar radiation and maintaining the balance of atmospheric constituents. Water scarcity is the predominant feature of arid lands. In hyperarid, arid and semiarid regions, water is scarce most of the time, and human settlements may cluster around rare sources of water such as rivers, springs, wells and oases. These arid lands are also characterized by persistent water scarcity, frequent drought, high climatic variability and various forms of land degradation, including desertification and loss of biodiversity. These areas occupy 41% area of the earth’s land surface and are home to roughly 2.5 billion people who rely directly on arid land ecosystem services for their livelihoods and support 50% of the world’s livestock where 44% of the world’s food is grown. As per the aridity index, there are four categories of arid lands, hyperarid, arid, semiarid and dry subhumid regions. Livelihood sustainability in these regions is threatened by a complex and interrelated range of social, economic and environmental changes that present significant challenges to researchers, policymakers and, above all, rural land users. The present chapter provides an introductory overview of arid lands of the world, its distribution, causes of aridity, inhabitants and various types of land uses for livelihood.