Drought

Posted by Craig Clarke

on Dec 19, 2011

by Paul Engleman The Rotarian -- December 2011

A drought is an extended period during which a region experiences a deficit in its water supply. Unlike a desert, which is an area known for having little rainfall, a region experiencing drought is undergoing a temporary climatic condition.

Droughts can be hydrological, when water levels in a region’s lakes and reservoirs are low, and meteorological, when precipitation is below what’s considered normal for an area. Severe droughts can be agricultural, when dry conditions affect crop production and the natural distribution of local species.

The National Drought Mitigation Center at the University of Nebraska, Lincoln, maintains a U.S. Drought Monitor, which rates drought conditions according to four levels of intensity: moderate, severe, extreme, and exceptional. The monitor uses the term abnormally dry to identify areas that are not yet in drought or that are recovering from drought. In July, the center reported that the percentage of contiguous U.S. land area experiencing exceptional drought was the highest in the country’s history.

The U.S. National Weather Service recognizes three categories of drought: dry spell, with less than 0.03 inch of precipitation for at least 15 consecutive days; partial drought, when the average daily precipitation is 0.008 inch or less over 29 days; and absolute drought, with no measurable precipitation for at least 15 days.

The most infamous drought in the United States was the Dust Bowl of the 1930s. It covered nearly 50 million acres in parts of Colorado, Kansas, New Mexico, Oklahoma, and Texas, and drove thousands of farmers to abandon their land.

The deadliest drought in recorded history occurred in China, from 1876 to 1879. It was so severe that most crops and livestock died, resulting in a loss of food production that affected more than 600,000 square miles and nine provinces. The estimated death toll from the subsequent famine was nine million.

Although droughts can happen in any part of the world, some regions are regarded as drought-prone, including Africa, the Middle East, Asia, Australia, and parts of South America. The main cause of drought is a lack of atmospheric water vapor, which results in low precipitation. This atmospheric condition can stem from shifting winds and dry, high-pressure zones. Drought can also be caused by deforestation, which inhibits moisture retention in soil.

East Africa is experiencing its worst drought in 60 years, with no rainfall for more than a year in an area stretching from Kenya through Somalia and into Ethiopia. The result has been widespread famine: The UN Office for the Coordination of Humanitarian Affairs reports that more than 12.4 million people are in need of help. The current forecast is for below-average precipitation in the next rainfall season, increasing the likelihood that emergency conditions will continue well into next year.