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A drought is a period of drier-than-normal conditions.Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, and O. Zolina, 2021: Water Cycle Changes . In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Masson-Delmotte,. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1055–1210, doi:10.1017/9781009157896.010. A drought can last for days, months or years. Drought often has large impacts on the and agriculture of affected regions, and causes harm to the local economy. Living With Drought Australian Drought and Climate Change . Retrieved June 7th 2007. Annual dry seasons in the tropics significantly increase the chances of a drought developing, with subsequent increased wildfire risks. 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 , more and larger wildfires, loss of biodiversity.
Economic impacts of drought result due to negative disruptions to agriculture and livestock farming (causing Food security), forestry, public Water supply, river navigation (due to e.g.: lower water levels), electric power supply (by affecting hydropower systems) and impacts on human health.
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. Drought can also lead to increased air pollution due to increased dust concentrations and . Prolonged droughts have caused 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 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.
According to National Integrated Drought Information System, a multi-agency partnership, drought is generally defined as "a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage". The National Weather Service office of the NOAA defines drought as "a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area".
Drought is a complex phenomenon − relating to the absence of water − which is difficult to monitor and define. By the early 1980s, over 150 definitions of "drought" had already been published. The range of definitions reflects differences in regions, needs, and disciplinary approaches.
The different categories of droughts have different causes but similar effects:
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.
Careful monitoring of moisture levels can also help predict increased risk for wildfires.
Precipitation can be divided into three categories, based on whether it falls as liquid water, liquid water that freezes on contact with the surface, or ice.
Droughts occur mainly in areas where normal levels of rainfall are, in themselves, low. If these factors do not support precipitation volumes sufficiently to reach the surface over a sufficient time, the result is a drought. Drought can be triggered by a high level of reflected sunlight and above average prevalence of high , carrying continental, rather than oceanic air masses, and ridges of high pressure areas aloft can prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Once a region is within drought, feedback mechanisms such as local arid air, hot conditions which can promote warm core ridging, and minimal evapotranspiration can worsen drought conditions.
Conversely, during El Niño events, drier and hotter weather occurs in parts of the Amazon River Basin, Colombia, and Central America. Winters during the El Niño are warmer and drier than average conditions in the Northwest, northern Midwest, and northern Mideast United States, so those regions experience reduced snowfalls. Conditions are also drier than normal from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, and Botswana. Direct effects of El Niño resulting in drier conditions occur in parts of Southeast Asia and Northern Australia, increasing , worsening haze, and decreasing air quality dramatically. Drier-than-normal conditions are also in general observed in Queensland, inland Victoria, inland New South Wales, and eastern Tasmania from June to August. As warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, it causes extensive drought in the western Pacific. Singapore experienced the driest February in 2014 since records began in 1869, with only 6.3 mm of rain falling in the month and temperatures hitting as high as 35 °C on 26 February. The years 1968 and 2005 had the next driest Februaries, when 8.4 mm of rain fell.
The IPCC Sixth Assessment Report also pointed out that "Warming over land drives an increase in atmospheric evaporative demand and in the severity of drought events"Douville, H., K. Raghavan, J. Renwick, R.P. Allan, P.A. Arias, M. Barlow, R. Cerezo-Mota, A. Cherchi, T.Y. Gan, J. Gergis, D. Jiang, A. Khan, W. Pokam Mba, D. Rosenfeld, J. Tierney, and O. Zolina, 2021: Chapter 8: Water Cycle Changes. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change Masson-Delmotte,. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1055–1210, doi:10.1017/9781009157896.010. and "Increased atmospheric evaporative demand increases plant water stress, leading to agricultural and ecological drought".Caretta, M.A., A. Mukherji, M. Arfanuzzaman, R.A. Betts, A. Gelfan, Y. Hirabayashi, T.K. Lissner, J. Liu, E. Lopez Gunn, R. Morgan, S. Mwanga, and S. Supratid, 2022: Chapter 4: Water. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change H.-O.. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 551–712, doi:10.1017/9781009325844.006.
There is a rise of compound warm-season droughts in Europe that are concurrent with an increase in potential evapotranspiration.
One can divide the impacts of droughts and water shortages into three groups: environmental, economic and social (including health).
Economic losses as a result of droughts include lower agricultural, forests, game and fishing output, higher food-production costs, lower energy-production levels in hydro plants, losses caused by depleted water tourism and transport revenue, problems with water supply for the Energy industry and for technological processes in metallurgy, mining, the chemical, paper, wood, foodstuff industries etc., disruption of Water supply for municipal economies.
Further examples of common environmental and economic consequences of drought include:
Water stress affects plant development and quality in a variety of ways: firstly drought can cause poor germination and impaired seedling development. At the same time plant growth relies on cellular division, cell enlargement, and differentiation. Drought stress impairs mitosis and cell elongation via loss of turgor pressure which results in poor growth. Development of leaves is also dependent upon turgor pressure, concentration of nutrients, and carbon assimilates all of which are reduced by drought conditions, thus drought stress lead to a decrease in leaf size and number. Plant height, biomass, leaf size and stem girth has been shown to decrease in maize under water limiting conditions. Crop yield is also negatively effected by drought stress, the reduction in crop yield results from a decrease in photosynthetic rate, changes in leaf development, and altered allocation of resources all due to drought stress. Crop plants exposed to drought stress suffer from reductions in leaf water potential and transpiration rate. Water-use efficiency increases in crops such as wheat while decreasing in others, such as potatoes.
Plants need water for the uptake of nutrients from the soil, and for the transport of nutrients throughout the plant: drought conditions limit these functions leading to stunted growth. Drought stress also causes a decrease in photosynthetic activity in plants due to the reduction of photosynthetic tissues, stomatal closure, and reduced performance of photosynthetic machinery. This reduction in photosynthetic activity contributes to the reduction in plant growth and yields. Another factor influencing reduced plant growth and yields include the allocation of resources; following drought stress plants will allocate more resources to roots to aid in water uptake increasing root growth and reducing the growth of other plant parts while decreasing yields.
There are negative effects on the health of people who are directly exposed to this phenomenon (excessive ). Droughts can also cause limitations of water supplies, increased water pollution levels, high food-costs, stress caused by failed harvests, water scarcity, etc. Reduced water quality can occur because lower water-flows reduce dilution of pollutants and increase contamination of remaining water sources.Mosley LM (2014). Drought impacts on the water quality of freshwater systems; review and integration. Earth-Science Reviewss. .10. Mosley LM, Zammit B, Leyden E, Heneker TM, Hipsey MR, Skinner D, and Aldridge KT (2012). The Impact of Extreme Low Flows on the Water Quality of the Lower Murray River and Lakes (South Australia). Water Resources Management 26: 3923–3946.
This explains why droughts and water scarcity operate as a factor which increases the gap between developed and developing countries.
Effects vary according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they do not have alternative food-sources. Areas with populations that depend on water sources as a major food-source are more vulnerable to famine. Further examples of social and health consequences include:
High levels of microcystin appeared in San Francisco Bay Area salt-water shellfish and fresh-water supplies throughout the state of California in 2016.
Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, , pale yellow or buff, windblown (Aeolian) sediment. It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces. Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world. Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.
By far the largest part of Australia is desert or semi-arid lands commonly known as the outback. A 2005 study by Australian and American researchers investigated the desertification of the interior, and suggested that one explanation was related to human settlers who arrived about 50,000 years ago. Regular burning by these settlers could have prevented from reaching interior Australia. Sensitivity of the Australian Monsoon to insolation and vegetation: Implications for human impact on continental moisture balance , Geological Society of America In June 2008 it became known that an expert panel had warned of long term, maybe irreversible, severe ecological damage for the whole Murray-Darling basin if it did not receive sufficient water by October 2008. Australian rivers 'face disaster' , BBC News Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008. Australia faces worse, more frequent droughts: study , Reuters Australian environmentalist Tim Flannery, predicted that unless it made drastic changes, Perth in Western Australia could become the world's first ghost town, an abandoned city with no more water to sustain its population. Metropolis strives to meet its thirst , BBC News The long Australian Millennial drought broke in 2010.
The Eastern African region experiences the impacts of climate change in different forms. For instance, below-average rainfall occurred for six consecutive rainy seasons in the Horn of Africa during the period 2020–2023 leading to the third longest and most widespread drought on record with dire implications for food security (see Horn of Africa drought (2020–present)). Conversely, other parts experienced extreme floods, e.g., the 2020 East Africa floods in Ethiopia, Rwanda, Kenya, Burundi, and Uganda, and the 2022 floods in South Sudan.
A key feature in the region is the heterogeneous distribution of hydrologic extremes in space and time. For instance, El Niño can cause droughts in one part of the region and floods in the other. This is also a common situation within a country, e.g., in Ethiopia. The recent years with consecutive droughts followed by floods are a testament to the need to better forecast these kinds of events and their impacts.
/ref> Drought in India affecting the Ganges is of particular concern, as it provides drinking water and agricultural irrigation for more than 500 million people. In 2025, the UN warned that retreating glaciers could threaten the food and water supply of 2 billion people worldwide.
See also:
Strategies for drought protection or mitigation include:
Droughts can be scientifically explained in terms of physical mechanisms, which underlie natural disasters and are influenced by human impact on the environment. 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. 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.
Historically, rituals have been used in an attempt to prevent or avert drought. Rainmaking rituals have ranged from dances to scapegoating to . Many ancient practices are now a matter of folklore while others may still be practiced.
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. 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.
Some historical droughts include:
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