# title
HYDROLOGY, FLOODS AND DROUGHTS | Deserts and Desertification

# abstract
2015 Elsevier Ltd. All rights reserved. Deserts cover about 35% of the land surface area of the world and are typically located between and astride the Tropic of Cancer (35 N) and the Tropic of Capricorn (35 S). About 20% of the world's population resides in this geographic region. The location of this global arid zone is primarily the result of the semi-permanent high-pressure cells that dominate this region along with such other factors as rain-shadow effects, continentality or remoteness from moisture sources, upwelling of cold currents that suppress the development of precipitation, and the nature and direction of the prevailing winds. Most deserts exhibit a combination of the above factors. Desertification refers to land degradation in the global arid zone owing to a series of complex climatic, biophysical, and anthropogenic factors and became a major global topic during the severe drought of the Sahel region in northern Africa in the 1970s. Desertification has been erroneously represented as the irreversible march of the desert and is now believed to result primarily from the degradation of arid ecosystems largely because of human induced factors along with natural climatic oscillations and drought cycles.