Drought

Introduction

Drought occurs when weather conditions are unusually dry over a period of time. Drought can occur in all climatic regions of the world, but tends to be worse and more frequent in semiarid places. The main consequence of a drought is a water shortage, which may soon have an adverse effect on human activities and well-being. Crop damage is one obvious early impact of a drought, leading to poverty and famine in vulnerable parts of the world like Africa.

Meteorologists can try to predict drought by monitoring rainfall and analyzing weather patterns. Water conservation measures may offset some of the harmful effects of a drought. It appears that droughts are becoming more widespread and more frequent, probably because of the effects of global warming. The existence of drought should focus attention on water as a precious resource that should never be wasted.

Historical Background and Scientific Foundations

The hydrological cycle is a natural process where water is recycled and purified. It evaporates into the air from lakes, rivers, or the ocean and eventually falls back down as precipitation in the form of rain or snow. Any disturbance of the hydrological cycle may lead to a period of reduced, or no, precipitation known as a drought. Precipitation depends on water vapor being carried by wind from a water source. But if these moisture-containing winds are replaced by dry winds, or become part of an anticyclone system, then the weather becomes dry and the sky persistently cloudless, setting the scene for a drought.

A drought may be short-lived or it may last for many years. A drought lasting for less than 14 days is generally known as a dry spell. Droughts tend to be cyclical. In the United States, they tend to occur every 22 years, with the midwestern states being most severely affected. The famous drought of 1933–1935, known as the Dust Bowl, affected 50 million acres in the Great Plains area bringing disaster to farmers through failed crops. This drought followed more than a decade of wind-driven soil erosion in the region, driven by intense agricultural cultivation and loss of natural windbreaks. In 1970 there was a severe drought in California lasting around 18 months. Temperatures soared and wildfires broke out in the dry conditions, causing millions of dollars worth of damage.

Drought can be defined in four different ways. Meteorological drought refers to how much precipitation has departed from its normal level for that region. In absolute terms, a drought in a particularly wet region would not be defined as such in a dry region. An agricultural drought occurs when the amount of water in the soil is no longer adequate to meet the needs of a particular crop. There is therefore a great deal of value in planting drought-resistant crops in drought-prone regions. Hydrological drought occurs when the surface and subsurface water supplies fall below what would normally be expected. A socioeconomic drought is one that has a clear impact on human activity, causing economic losses, health problems, or social unrest.

Impacts and Issues

The impact of a drought depends on how severe the lack of precipitation is, how long it lasts, and the size of the area affected. Droughts tend to be worse in semiarid places and those affected by human-made activity. Natural ecosystems often survive a drought through their adaptation to local dry conditions whereas domestic animals and introduced crops do not.

WORDS TO KNOW

DRY SPELL: A short period of drought, usually lasting less than 14 days.

HYDROLOGIC CYCLE: The overall process of evaporation, vertical and horizontal transport of vapor, condensation, precipitation, and the flow of water from continents to oceans.

RESERVOIR: The collection of naturally occurring fluids in the porosity of a subsurface rock formation.

Water is essential to life and most human economic and social activities. Drought causes crop damage, hunger, and disease through decreasing water supplies. It can also cause soil erosion, desertification, and the spread of forest fires. Drought is sometimes a factor in war. For instance, Arab pastoralists and African farmers co-existed peacefully in the Sudan until water scarcity created tensions. This is a factor in the genocide in the Darfur region.

Global warming appears to be increasing the frequency of drought and will do so in the future. Researchers for the National Center for Atmospheric Research say that the percentage of Earth’s land area affected by serious drought has more than doubled since the 1970s. To offset the impact of drought, water conservation must become a top priority.

See Also Desertification; Deserts; Precipitation; Surface Water; Water Conservation; Water Resources; Water Supply and Demand

BIBLIOGRAPHY

Books

Cunningham, W.P., and A. Cunningham. Environmental Science: A Global Concern. New York: McGraw-Hill International Edition, 2008.

Web Sites

National Weather Service Forecast Office. “What Is Meant by the Term Drought? http://www.wrh.noaa.gov/fgz/science/drought.hph?wfo=fgz (accessed February 22, 2008).

Think Quest. “Drought.” http://library.thinkquest.org/16132/html/drought.html (accessed February 22, 2008).

The University Corporation for Atmospheric Research. “Drought’s Growing Reach: NCAR Study Points to Global Warming as Key Factor.” January 10, 2005. http://www.ucar.edu/news/releases/2005/drought_research.shtml (accessed February 22, 2008).