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A drought is a climate event marked by a prolonged period of decreased rainfall. Droughts are in fact part of the natural climate cycle in many regions of the world, but they can still be extremely disruptive, especially when the impact of the drought is increased by human activities. Drought conditions are of interest socially, politically, economically, and environmentally, and at any given time, several regions of the world are often experiencing dry conditions.
In a simple meteorological drought, rainfall is lower than average, or lower than expected, for a period of several months. This can deepen into a hydrologic situation, in which overall water supplies are low and conflicts over water resources may emerge, in which case an agricultural drought, in which crops and livestock suffer, may also emerge.
Droughts can be accompanied with major climate changes, such as an increase in average temperatures, or unusually high winds. The hot, dry weather can contribute to desertification, and it can also lead to dust storms and wildfires. Arguments over natural resources can become extremely fraught during drought conditions, as for example when two nations go to war over a shared water source on the border, or when people migrate en masse to find land which is not suffering from drought.
A number of changes can occur in the natural environment during a drought. Algae tends to proliferate in water sources because of the elevated temperatures and decreased water supply, and the algae blooms can choke out fish species and make animals sick. The landscape may also change radically as plants, trees, and shrubs die from lack of water, and hardy opportunistic species move in to eke out a living. This can also change the animal demographics in the natural environment, with drought-sensitive animals disappearing along with fragile plants.
When regions or nations suspect that drought conditions are emerging, they often take steps to reduce the impact and raise awareness. Citizens may be asked to be more careful about their water usage, for example, and arrangements can be made to ship in water from other locations to keep water supplies stable. Appeals may also be made for international aid in the form of water supplies, food to replace damaged crops, and peacekeeping troops to deal with outbreaks of violence over scarce resources.
Recovery can take some time, even as rainfall starts to return to normal levels. The snowpack usually shrinks radically, decreasing the supply of stored water, and the land may need careful tending to recover as plants and animals re-establish themselves. The social chaos which severe droughts can cause may also have long lasting repercussions.