It might make folks feel better for awhile, provide cooling, and make the vegetation perk up. Likewise, a single rainstorm will not break the drought, but it may provide temporary relief.Ī light to moderate shower will probably only provide cosmetic relief. A single dose of medicine can alleviate symptoms of illness, but it usually takes a sustained program of medication to cure an illness. A good analogy might be how medicine and illness relate to each other. Rainfall in any form will provide some drought relief. Why doesn't a drought go away when it rains? During cool, cloudy weather, evapotranspiration rates may be small enough to offset periods of below-normal precipitation and a drought may be less severe or may not develop at all (Moreland, 1993). When evapotranspiration rates are large, soils can lose moisture and dry conditions can develop. Sunlight, humidity, temperature, and wind affect the rate of evapotranspiration. The total amount of water returned to the air by these processes is called evapotranspiration. Plant roots draw some of the moisture from the soil and return it to the air through a process called transpiration. Some rain returns to the air as water vapor when water evaporates from water surfaces and from moist soil. Water levels in wells may not reflect a shortage of rainfall for a year or more after a drought begins (Moreland, 1993).ĭoes a shortage of rain mean that a drought will occur?Ī period of below-normal rainfall does not necessarily result in drought conditions. The effects of a drought on flow in streams and reservoirs may not be noticed for several weeks or months. Within a short period of time, the amount of moisture in soils can begin to decrease. The first evidence of drought usually is seen in records of rainfall. That extended dry period produced the "Dust Bowl" of the 1930's when dust storms destroyed crops and farms. In Missouri, the drought lasted from 1930 to 1941. In California, the drought extended from 1928 to 1937. During the 1930's, most of the United States was much drier than normal. Dry periods can last for 10 years or more. The end of a drought can occur as gradually as it began. Several weeks, months, or even years may pass before people know that a drought is occurring. The beginning of a drought is difficult to determine. If dry weather persists and water-supply problems develop, the dry period can become a drought (Moreland, 1993). When rainfall is less than normal for several weeks, months, or years, the flow of streams and rivers declines, water levels in lakes and reservoirs fall, and the depth to water in wells increases. When little or no rain falls, soils can dry out and plants can die. Even if the total amount of rainfall for a year is about average, rainfall shortages can occur during a period when moisture is critically needed for plant growth, such as in the early summer. In Georgia, most of the yearly precipitation falls during winter, early spring, and in July. The amount of rain and snow also varies with the seasons. In contrast, the average yearly precipitation in Atlanta is about 50 inches. In the deserts of the Southwest, the average precipitation is less than 3 inches per year. The amount of precipitation at a particular location varies from year to year, but over a period of years, the average amount is fairly constant. Precipitation (rain or snow) falls in uneven patterns across the country. To a hydrologist, a drought is an extended period of decreased precipitation and streamflow.Ī drought is a period of drier-than-normal conditions that results in water-related problems. To a water manager, a drought is a deficiency in water supply that affects water availability and water quality. To a meteorologist, a drought is a prolonged period when precipitation is less than normal. To a farmer, a drought is a period of moisture deficiency that affects the crops under cultivation-even two weeks without rainfall can stress many crops during certain periods of the growing cycle. The word "drought" has various meanings, depending on a person's perspective. Droughts do not have the immediate effects of floods, but sustained droughts can cause economic stress throughout an area. While it is relatively easy to define what a hurricane or earthquake is, defining a drought is more subjective. (Credit: Alan Cressler, USGS) What is a drought?
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