Drought
A drought is a period of drier-than-normal conditions.[1]: 1157 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.[2][3] Annual dry seasons in the tropics significantly increase the chances of a drought developing, with subsequent increased wildfire risks.[4] Heat waves can significantly worsen drought conditions by increasing evapotranspiration.[5] This dries out forests and other vegetation, and increases the amount of fuel for wildfires.[4][6]
For other uses, see Drought (disambiguation).
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.[7][8]
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.[9][10] Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008.[11] 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.[12][13] 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.[14]
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.
Several indices have been defined to quantify and monitor drought at different spatial and temporal scales. A key property of drought indices is their spatial comparability, and they must be statistically robust.[22] Drought indices include:[22]
High-resolution drought information helps to better assess the spatial and temporal changes and variability in drought duration, severity, and magnitude at a much finer scale. This supports the development of site-specific adaptation measures.[22]
The application of multiple indices using different datasets helps to better manage and monitor droughts than using a single dataset, This is particularly the case in regions of the world where not enough data is available such as Africa and South America. Using a single dataset can be limiting, as it may not capture the full spectrum of drought characteristics and impacts.[22]
Careful monitoring of moisture levels can also help predict increased risk for wildfires.
Droughts in particular countries:
See also:
Agriculturally, people can effectively mitigate much of the impact of drought through irrigation and crop rotation. Failure to develop adequate drought mitigation strategies carries a grave human cost in the modern era, exacerbated by ever-increasing population densities.
Strategies for drought protection or mitigation include:
When water is scarce due to droughts, there are a range of options for people to access other sources of water, such as wastewater reuse, rainwater harvesting and stormwater recovery, or seawater desalination.
Throughout history, humans have usually viewed droughts as disasters due to the impact on food availability and the rest of society. Drought is among the earliest documented climatic events, present in the Epic of Gilgamesh and tied to the Biblical story of Joseph's arrival in and the later Exodus from ancient Egypt.[102] Hunter-gatherer migrations in 9,500 BC Chile have been linked to the phenomenon,[103] as has the exodus of early humans out of Africa and into the rest of the world around 135,000 years ago.[104]
Droughts can be scientifically explained in terms of physical mechanisms, which underlie natural disasters and are influenced by human impact on the environment.[105]
Beliefs about drought are further shaped by cultural factors including local knowledge, perceptions, values, beliefs and religion. In some places and times, droughts have been interpreted as the work of supernatural forces.[106] Globally, people in many societies have been more likely to explain natural events like drought, famine and disease in terms of the supernatural than they are to explain social phenomena like war, murder, and theft.[107][108]
Historically, rituals have been used in an attempt to prevent or avert drought. Rainmaking rituals have ranged from dances to scapegoating to human sacrifices. Many ancient practices are now a matter of folklore while others may still be practiced.[109]
In areas where people have limited understanding of the scientific basis of drought, beliefs about drought continue to reflect indigenous beliefs in the power of spirits and Christian philosophies that see drought as a divine punishment. Such beliefs can influence people's thinking and affect their resilience and ability to adapt to stress and respond to crises.[106] In the case of Creationism, curricula sometimes give religious explanations of natural phenomena rather than scientific ones. Teaching explicitly denies evolution, that human agency is affecting climate, and that climate change is occurring.[110]
Some historical droughts include:
