Drought is a non-seasonal climatic condition in which there is a period of moderate to high heat and not enough rainfall to sustain native plant and wildlife. Formally, it may be defined as "a period of abnormally dry weather sufficiently prolonged from the lack of precipitation to cause a serious hydrologic imbalance." .
Droughts can be mild to severe, and the longer a drought continues, the more serious its impact on the environment. Plants and animals die, or animals may travel to other areas in order to survive.
Humans living in drought-stricken areas are particularly vulnerable. Most humans do not live nomadic lifestyles, so they find it difficult to simply move to another area, leaving their established settlements.
Hobbyists may have their stock spoilt by the effects of drought, but this is a small inconvenience compared with the human cost of severe drought.
Severe drought ruins crops, and so can cause rampant starvation and attendant disease which can wipe out entire populations. Even where the effects are less devastating, drought adversely affects the livelihood of farmers and others in the agricultural sectors.
Because water tables can be reduced during droughts, cities and states can place mandatory water-use restrictions in order to conserve as much water as possible to avois endangering its populace. During this time it may be unlawful to water grass or plants, or they may only receive city water on a restricted schedule.
Drought may be quantified with a numerical value that is related to some of the cumulative effects of a prolonged and abnormal moisture deficiency.