No 58 : THE IMPACT OF GLOBAL WARMING :Extreme Dry

Extreme Dry

While some regions are likely to get wetter as the world warms, other regions that are already on the dry side are likely to get drier.

Global warming affects evapotranspiration—the movement of water into the atmosphere from land and water surfaces and plants due to evaporation and transpiration— which is expected to lead to:

• Increased drought in dry areas. In drier regions, evapotranspiration may produce periods of drought—defined as below-normal levels of rivers, lakes, and groundwater, and lack of enough soil moisture in agricultural areas. Precipitation has declined in the tropics and subtropics since 1970. Southern Africa, the Sahel region of Africa, southern Asia, the Mediterranean, and the U.S. Southwest, for example, are getting drier. Even areas that remain relatively wet can experience long, dry conditions between extreme precipitation events.
• Expansion of dry areas. Scientists expect the amount of land affected by drought to grow by mid-century—and water resources in affected areas to decline as much as 30 percent. These changes occur partly because of an expanding atmospheric circulation pattern known as the Hadley Cell—in which warm air in the tropics rises, loses moisture to tropical thunderstorms, and descends in the subtropics as dry air. As jet streams continue to shift to higher latitudes, and storm patterns shift along with them, semi-arid and desert areas are expected to expand.

Tweet