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Drought Definitions

Agriculture
Agriculture (from Agri Latin for ager ("a field"), and culture, from the Latin cultura "cultivation" in the strict sense of "tillage of the soil". A literal reading of the English word yields "tillage of the soil of a field".) is the production of food, feed, fiber and other goods by the systematic raising of domesticated plants and animals. In modern usage, the word agriculture covers all activities essential to food/feed/fiber production, including all techniques for raising and "processing" livestock. Agriculture is also short for the study of the practice of agriculture — more formally known as agricultural science.
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damage and harm the local economy.

Stages of Drought
As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases. Droughts go through three stages before their ultimate cessation:
1.) Meteorological drought is brought about when there is a prolonged period with less than average precipitation. Meteorological drought usually precedes the other kinds of drought.
2.) Agricultural droughts are droughts that affect crop production or the ecology of the range. This condition can also arise independently from any change in precipitation levels when soil conditions and erosion triggered by poorly planned agricultural endeavors cause a shortfall in water available to the crops. However, in a traditional drought, it is caused by an extended period of below average precipitation.
3.) Hydrological drought is brought about when the water reserves available in sources such as aquifers, lakes and reservoirs falls below the statistical average. Like an agricultural drought, this can be triggered by more than just a loss of rainfall. For instance, Kazakhstan was recently awarded a large amount of money by the World Bank to restore water that had been diverted to other nations from the Aral Sea under Soviet rule. Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out.
Economy
An economy is the system of human activities related to the production, distribution, exchange, and consumption of goods and services of a country or other area.
The composition of a given economy is inseparable from technological evolution, civilization's history and social organization, as well as from Earth's geography and ecology, e.g. ecoregions which represent different agricultural and resource extraction opportunities, among other factors.
Ecosystem
An ecosystem is a natural system consisting of all plants, animals and microorganisms (biotic factors) in an area functioning together with all the non-living physical (abiotic) factors of the environment.

The term ecosystem was coined in 1930 by Roy Clapham, to denote the physical and biological components of an environment considered in relation to each other as a unit. British ecologist Arthur Tansley later refined the term, describing it as the interactive system established between biocoenosis (a group of living creatures) and their biotope (the environment in which they live).
Precipitation
In meteorology, precipitation (also known as hydrometeor) is any product of the condensation of atmospheric water vapor that is deposited on the earth's surface. It occurs when the atmosphere (being a large gaseous solution) becomes saturated with water vapour and the water condenses and falls out of solution (i.e., precipitates). Air becomes saturated via two processes, cooling and adding moisture.

Precipitation that reaches the surface of the earth can occur in many different forms, including rain, freezing rain, drizzle, snow, sleet, and hail. Virga is precipitation that begins falling to the earth but evaporates before reaching the surface. Precipitation is a major component of the hydrologic cycle, and is responsible for depositing most of the fresh water on the planet. Approximately 505,000 km³ of water falls as precipitation each year, 398,000 km³ of it over the oceans. Given the Earth's surface area, that means the globally-averaged annual precipitation is about 1 m, and the average annual precipitation over oceans is about 1.1 m.

Definitions obtained from http://encyclopedia.thefreedictionary.com

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