A Drought occurs when there is less than 0.2mm (1/100in) of rainfall in an area over a period of about two weeks. Droughts are usually caused by an area of high pressure that remains in one place for a long period of time. This is called a blocking high. The blocking high will prevent the movement of low-pressure systems into an area, meaning that hot, dry weather will dominate that area, leading to a drought. Parts of Africa, Asia and Central America often experience periods of drought.
A drought is a prolonged period with less-than-average amounts of rain or snow in a particular region. The severity of the drought depends on the amount of time that a region receives below-average precipitation.
For example, a few weeks without rain could stress a farmer’s crops during the growing season. This is called a flash drought. But it could take a much longer dry period to see a full drought that would affect a region’s water supply.
A drought is caused by drier than normal conditions that can eventually lead to water supply problems. Really hot temperatures can make a drought worse by causing moisture to evaporate from the soil. Just because a region is hot and dry doesn’t necessarily mean it is going through a drought. Droughts only occur when an area is abnormally dry. Here’s why:
Rain and snow don’t fall evenly across Earth. Some regions are routinely wet and others are routinely dry. From season to season — and from year to year — the amount of rain or snow in a location can vary.
However, over a period of many years, the average amount of precipitation in a region is fairly consistent. For example, in the deserts of the American Southwest, the average precipitation is less than 3 inches per year. But, the average yearly precipitation in Atlanta is about 50 inches.
When a particular area gets less rain than usual, the soil gets much less moisture, too. The soil starts drying out and plants die. When this pattern continues for several weeks, months or years, the flow of streams and rivers decreases and water levels in lakes, reservoirs and wells fall. Eventually, the unusual dry weather causes water supply issues, and the dry period becomes a drought.
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