Although earth has plenty of water, it is distributed unevenly, and serious water supply problems exist. In regions where freshwater is in short supply, such as deserts, obtaining it becomes critically important. Arid lands, or deserts, are fragile ecosystems in which plant growth is limited by lack of precipitation. Semiarid lands receive more precipitation than deserts but are subject to frequent and prolonged droughts. Forty percent of the world's population lives in arid and semiarid lands, primarily in Asia and Africa.
Droughts are exceptional meteorological events.
Water scarcity can be measured by the number of people per unit of available freshwater. While the symptoms of water scarcity are easy to identify, its causes are not. The first two of these causes relate to the climate, the second two to changes that result from human activity. Jointly or separately, climate and human activity are depriving millions of people of the water they need. Yemen lies in the southwest corner of the Arabian Peninsula, surrounded by the Red Sea from the west, Saudi Arabia from the north, Oman from the east, and the Arabian Sea from the south.