period of unusually low precipitation.
A drought is a period of drier-than-normal conditions. A drought can last for days, months or years. Drought often has large impacts on the ecosystems and agriculture of affected regions, and causes harm to the local economy. Annual dry seasons in the tropics significantly increase the chances of a drought developing, with subsequent increased wildfire risks. Heat waves can significantly worsen drought conditions by increasing evapotranspiration. This dries out forests and other vegetation, and increases the amount of fuel for wildfires.
Drought is a recurring feature of the climate in most parts of the world, becoming more extreme and less predictable due to climate change, which dendrochronological studies date back to 1900. There are three kinds of drought effects, environmental, economic and social. Environmental effects include the drying of wetlands, more and larger wildfires, loss of biodiversity.
Economic impacts include disruption of water supplies for people, less agricultural productivity and therefore more expensive food production. Another impact is shortages of water for irrigation or hydropower. Social and health costs include the negative effect on the health of people directly exposed to this phenomenon (excessive heat waves), high food costs, stress caused by failed harvests, water scarcity, etc. Prolonged droughts have caused mass migrations and humanitarian crisis.
Examples for regions with increased drought risks are the Amazon basin, Australia, the Sahel region and India. For example, in 2005, parts of the Amazon basin experienced the worst drought in 100 years. Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. The long Australian Millennial drought broke in 2010. The 2020–2022 Horn of Africa drought has surpassed the horrific drought in 2010–2011 in both duration and severity. More than 150 districts in India are drought vulnerable, mostly concentrated in the state of Rajasthan, Gujarat, Madhya Pradesh and its adjoining Chhattisgarh, Uttar Pradesh, northern Karnataka and adjoining Maharashtra of the country.
Throughout history, humans have usually viewed droughts as disasters due to the impact on food availability and the rest of society. People have viewed drought as a natural disaster or as something influenced by human activity, or as a result of supernatural forces.