Introduction to dryland environments

Abstract

Exploration and awareness of drylands Drylands, simply defined, are areas where potential evaporative water loss balances or exceeds the meager annual rainfall; a shortage of water inherently plagues these regions. The drylands comprise one-third of the global land surface; they support 14% of the world’s inhabitants and a significant share of world agriculture. The climates of the drylands attracted little attention until the 1970s, when the combination of recurrent drought and intense land use demonstrated both the fragility and the importance of these ecosystems. The effects of climatic fluctuations and human-induced pressures have been especially adverse in semi-arid lands: agricultural regions of the American Midwest and Central Asia, India, the African Sahel, and much of southern Africa regularly have to contend with severe and often persistent drought. In the Sahel unusually dry conditions prevailed from the late 1960s until the turn of the twenty-first century. In some dryland regions climatic fluctuations and human mismanagement have interacted to initiate the process of desertification, a long-term degradation of the environment. Concern for the future is enhanced by the expansion of development into drylands as population growth continues, and by the prospect of global and regional climatic change. More unsettling are claims that human activities, including land use, may induce climatic change. Initially, knowledge about the world’s drylands was achieved in the context of exploration and exploitation, rather than scientific inquiry. German geographers such as Passarge (1904) and Jaeger (1921) wrote extensively about Namibia and South Africa. Missionaries such as Moffat and Livingstone (Fig. 1.1) kept detailed diaries that chronicled year-to-year environmental events at mission stations. French geographers and explorers, such as Capot-Rey (1953), Monod (1958), and Tilho (1911), vastly expanded our geographical knowledge of the Sahara. Huntington (1907) and Hedin (1904–5) journeyed into the Gobi Desert and other Asian regions. Powell (1875) and Gilbert (1975) surveyed the American West. Their journals included information on climate and weather, but the focus was on description, not physical processes. The field of meteorology was likewise slow to focus on dryland climates, understand their dynamics, or put them into a global context.