What is 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.

Types of Drought

Meteorological Drought

Meteorological drought is the amount of dryness and the duration of the dry period. Atmospheric conditions that result in deficiencies of precipitation change from area to area.

Agricultural Drought

Agricultural drought mainly effects food production and farming. Agricultural drought and precipitation shortages bring soil water deficits, reduced ground water or reservoir levels, and so on. Deficient topsoil moisture at planting may stop germination, leading to low plant populations.

Hydrological Drought

Hydrological drought is associated with the effects of periods of precipitation shortages on water supply. Water in hydrologic storage systems such as reservoirs and rivers are often used for multiple purposes such as flood control, irrigation, recreation, navigation, hydropower, and wildlife habitat. Competition for water in these storage systems escalates during drought and conflicts between water users increase significantly.

Socioeconomic Drought

Socioeconomic drought occurs when the demand for an economic good exceeds supply as a result of a weather-related shortfall in water supply.

Causes of Drought

Generally, rainfall is related to the amount of water vapour in the atmosphere, combined with the upward forcing of the air mass containing that water vapour. If either of these are reduced, the result is drought.

Factors include:

Deforestation
El Nino (and other oceanic temperature cycles)
Above average prevalence of high pressure systems
Winds carrying continental, rather than oceanic air masses (ie. reduced water content)
Some speculate that global warming will have a substantial impact on agriculture throughout the world, and especially in developing nations.

Drought Mitigation Strategies

Desalination of sea water for irrigation or consumption.
Drought monitoring - Continuous observation of rainfall levels and comparisons with current usage levels can help prevent man-made drought. For instance, analysis of water usage in Yemen has revealed that their water table (underground water level) is put at grave risk by over-use to fertilize their Khat crop. Careful monitoring of moisture levels can also help predict increased risk for wildfires, using such metrics as the Keetch-Byram Drought Index or Palmer Drought Index.
Land use - Carefully planned crop rotation can help to minimize erosion and allow farmers to plant less water-dependant crops in drier years.
Rainwater harvesting - Collection and storage of rainwater from roofs or other suitable catchments.
Recycled water - Former wastewater (sewage) that has been treated and purified for reuse.
Transvasement - Building canals or redirecting rivers as massive attempts at irrigation in drought-prone areas.
Water restrictions - Water use may be regulated (particularly outdoors). This may involve regulating the use of sprinklers, hoses or buckets on outdoor plants, the washing of motor vehicles or other outdoor hard surfaces (including roofs and paths), topping up of swimming pools, and also the fitting of water conservation devices inside the home (including shower heads, taps and dual flush toilets).
Reduction of Human population and animal pressure.
Cloud seeding - an artificial technique to induce rainfall.