What causes drought?
Drought can have devastating effects on people, animals and plants, though it's part of the natural weather cycle in many areas.
Cracked mud in dry creek bed | © Theo Allofs | Corbis
In popular culture, having a dry spell means going through some type of slump. But when it comes to weather, a dry spell has a particular name — "drought" — and it's no mere slump. Even though most parts of the world naturally experience drought as part of the weather cycle, periods of reduced or no rainfall — lasting weeks, months or even years — can have devastating effects on the people, animals and plants in an affected area.
MSN Weather: How to prepare for drought
Rainfall occurs when water vapor in clouds coalesces into droplets that grow heavy enough to fall at a speed greater than the cloud's rising air current, or updraft, meaning that the droplets reach the ground as precipitation. A number of factors — high pressure systems, reflected sunlight, weather cycles such as El Niño — can interfere with this cycle, resulting in little or no rain. If the interference goes on for long enough, a region will experience drought, which people think about in four ways:
Meteorological drought: How long is the drought, and how dry is it? This isn't a hard-and-fast definition. Areas that experience rainfall year-round (think humid Louisiana) will measure drought differently than regions that naturally go through extended periods of low rainfall (such as the arid Sonoran Desert in Arizona).
Agricultural drought: How does the drought affect a region's agriculture? A crop may be able to survive a drought if the plants got enough rainfall while they germinated. On the other hand, a drought that occurs early in the planting season might lead to reduced or no yields.
Hydrological drought: How does a drought affect a region's watershed? Farmers might feel the effects of low rainfall right away as their crops wither, but it could take much longer for anglers, rafters and hydroelectric companies to notice a river's reduced flow.
Socioeconomic drought: How does a lack of rainfall affect the economy? An area will see socioeconomic disruption if drought interrupts the supply of hydroelectric power, staple crops, fish, drinking water or other resources.
Quick facts about drought
- Drought is expected to become even more common as we start to see more effects of climate change.
- The notorious Dust Bowl of the 1930s was caused by many factors, but an extended drought in the Plains states was the tipping point that led to giant dust storms that blew away topsoil.
- Drought in the Horn of Africa in 1984-85 led to the starvation and death of 750,000 people.
- The drought of the summer of 2012 was one of the worst in U.S. history, affecting more than half of the country.