By the early 1980s researchers had published over 150 definitions of drought
Drought sounds simple, yet by the early 1980s more than 150 definitions were in print. The UN climate panel now settles for drier than normal. The trouble is that dryness can strike the sky, the rivers, the soil or the economy, and each shortage unfolds on its own timetable.
The IPCC's latest assessment frames drought as a moisture deficit compared with the usual water supply for a given place and season. American agencies add consequences: a shortfall of rain over a season or more that leaves too little water, or a moisture deficit harming people, animals or plants across a large area. The variety reflects different regions, needs and scientific disciplines.
Scientists sort droughts by where in the water cycle the gap appears. Meteorological drought is simply a long spell of below-average rain, and it usually comes first. Hydrological drought shows up later, as aquifers, lakes and reservoirs sink below normal; because it involves stored water being used faster than it refills, water management can make it better or worse. Agricultural or ecological drought stresses plants through evaporation and dry soil. Some add socioeconomic drought, when a weather-driven water shortfall pushes demand for a good past supply. Human diversion counts too: around 2007 the World Bank gave Kazakhstan substantial funds to restore water taken from the Aral Sea under Soviet rule.
The damage spreads widely. Wetlands dry out, wildfires grow larger and more frequent, and biodiversity suffers. Farms and herds fail, raising food insecurity, while forestry, drinking water, river shipping and hydropower all take hits. People face heat stress, expensive food, anxiety over lost harvests and dirtier air from dust and smoke. Long droughts have driven mass migrations and humanitarian emergencies. Heat waves make things worse by speeding evaporation from soil and plants, turning forests into fuel.
Drought recurs in most climates, but climate change is making it harsher and less predictable. In 2005 parts of the Amazon basin suffered their worst drought in a century. Australia's long Millennium drought ended in 2010, and the Horn of Africa drought of 2020 to 2022 outlasted and outdid the severe one of 2010 to 2011. Over history, people have blamed droughts on nature, on human actions or on supernatural forces.
Source: Drought
