This chapter examines current and future global drought conditions in the context of climate change, highlighting their climatic and other human-drivers. Drawing on original data analysis by the OECD and recent scientific literature, the chapter demonstrates how climate change is intensifying drought frequency and severity and shows how human development has exacerbated this risk in recent decades.
Global Drought Outlook
Trends, Impacts and Policies to Adapt to a Drier World
Abstract
Over the past decade, many regions of the world have faced extreme drought events that have caused severe economic and social consequences. The ongoing megadrought affecting Mexico and the United States – which has persisted for more than twenty years – is likely the most severe in 1 200 years (Williams, Cook and Smerdon, 2022[1]). In 2021, drought conditions in California caused economic costs of USD 1.1 billion for the agricultural sector alone (i.e. 2% of the sector’s annual revenues) (Public Policy Institute of California, 2022[2]). In 2022, a third of Europe’s territory experienced one of the worst droughts in the continent’s history, which, combined with an abnormally hot summer, cost more than EUR 40 billion (EEA, 2023[3]). In the same year, the Rhine River (Germany) reached its lowest depth in thirty years, forcing ships to operate at only 25-35% of their loading capacity (European Space Agency, 2022[4]). In the Horn of Africa, the region’s worst drought in forty years left 23 million people suffering severe hunger in 2023 (World Food Programme, 2023[5]). Overall, while droughts accounted for only 6% of all natural disasters that occurred between 1970 and 2019, they caused 34% of all disaster-related deaths, mostly due to famine in African countries (World Meteorological Organization (WMO), 2021[6]). Additionally, since 2010, over 3 million people have been displaced within their country to escape droughts (Internal Displacement Monitoring Centre, 2024[7]).
Climate change is set to worsen drought conditions, exacerbating other human pressures such as unsustainable land and water use. By increasing both temperature and precipitation variability, climate change facilitates periods of precipitation deficit and higher evaporation rates, leading to decreases in soil moisture, river flows, and groundwater levels (Vicente-Serrano et al., 2022[8]). The Intergovernmental Panel on Climate Change (IPCC) estimates that, under a +4°C warming scenario, average drought frequency and intensity may increase up to sevenfold in many regions compared to pre-industrial times (IPCC, 2021[9]). The causal link between climate change and specific drought events is increasingly demonstrated. For example, estimates suggest that climate change made the 2022 Northern Hemisphere drought twenty times more likely (Schumacher et al., 2022[10]) and has intensified the ongoing megadrought in North America by 42% (Williams, Cook and Smerdon, 2022[1]). These changes will compound existing pressures on water resources, such as increased water withdrawal for human consumption, industrial cooling, and irrigation, exacerbating the risk of water scarcity.
This chapter sheds light on the growing risk of drought in the context of climate change, showing the links between drought events and water availability and highlighting how human activities and climate change are intensifying drought risks. It includes existing scientific evidence and new analysis of various drought indicators by the OECD (see Annex B) to explore historical and future global trends in drought exposure in the context of climate change. The chapter outlines the key factors contributing to increasing drought risks, followed by an in-depth overview of how climate change is expected to exacerbate these conditions in the future.
2.2.1. What is drought?
Droughts are periods characterised by a significant hydrological imbalance in water sources or reservoirs, typically marked by "drier-than-normal" weather conditions. These periods are primarily driven by low rainfall and can be further intensified by high temperatures or strong wind, which accelerate water evaporation, as well as human activities (e.g. land or water use) (IPCC, 2022[11]). This imbalance affects various components of the water cycle, including soil moisture, surface water (e.g. lakes and rivers) levels, and groundwater reserves. The complexity of these interactions has led to numerous definitions of drought (Dracup, Lee and Paulson, 1980[12]; Wilhite and Glantz, 1985[13]), each emphasising an abnormal water deficit across different contexts and timescales.
Droughts are usually classified based on their main drivers and impacts (Figure 2.1):
Meteorological drought refers to a prolonged period of low precipitation.
Agricultural (or ecological) drought refers to a condition where soil moisture is insufficient to meet the needs of crops and vegetation.
Hydrological drought occurs when surface or groundwater water levels drop below average over a prolonged period.
How to read this figure: This figure should be read from left to right, with “+” or “–” symbols indicating the effect of the elements at the base of the arrow on those at the arrow’s head. Blue arrows represent the cascading effects of reduced precipitation and snow cover, orange arrows show the impact of rising temperatures, brown arrows indicate the effects of increased evaporation and evapotranspiration, and grey arrows represents the effect of radiation, wind, and CO₂ levels. For example, an increase in temperature reduces snowpack (–) and enhances evaporation and evapotranspiration (+). In turn, greater evaporation and evapotranspiration decrease soil moisture (agricultural drought) and surface water levels (hydrological drought).
Source: Author’s own, based on IPCC (2021[9]).
While interlinked, droughts are distinct from water scarcity, aridity, and desertification. In fact, droughts are characterised by below-average water or precipitation levels, while water scarcity refers to an imbalance between water supply and demand (IPCC, 2022[11]). Water scarcity can thus arise independently of drought conditions, such as when water extraction surpasses the renewable supply, or as a result of water pollution and infrastructure failures. Drought and aridity differ in their temporal nature. Whereas drought is a temporary phenomenon, aridity is a permanent climatic feature of regions with low rainfall and high evaporative demand, such as deserts. Desertification, on the other hand, refers to the process of land degradation in arid regions, driven not only by droughts but also by unsustainable human activities such as agricultural expansion, deforestation, and urbanisation (UNCCD, 2022[14]).
2.2.2. Observed changes in drought conditions
The share of global land exposed to droughts has significantly increased over the past decades, doubling between 1900 and 2020 (Figure 2.2). Regional observations show similar trends. For example, in Europe, drought-affected areas have expanded from the traditionally affected southern regions to encompass eastern and central parts of the continent (Joint Research Center, 2023[15]). In 2023, nearly half (48%) of the global land area experienced at least one month of extreme drought, the second-largest extent observed since 1951 (Romanello et al., 2024[16]).
Note: Areas identified as affected by drought in a given year are those where the Standardised Precipitation Evapotranspiration Index (SPEI) value falls below -1 (Jain et al., 2015[17]). The analysis represented in this figure excludes the Sahara Desert, the Gobi Desert, the Arabic Peninsula, and polar regions. The trend line shown in the figure is derived from a linear regression analysis of the annual proportion of global land affected by droughts over time.
Source: Author’s own, based on data from Beguería et al. (2023[18]).
Since the beginning of the 21st century, the frequency and intensity of drought events have increased in all continents. Around 40% of global land experienced an increase in both the average number of droughts and in their average intensity between the periods 1950-2000 and 2000-2020 (Figure 2.3 a and b). Extreme drought events – defined as years when the Standardised Precipitation Evapotranspiration1 Index (SPEI) value is less than or equal to -2 – have also become more frequent and severe in many regions over the last two decades compared to 1950-2000 (Figure 2.3 c and d) (Jain et al., 2015[17]). Hotspots of increased drought frequency and intensity include the Western United States, South America, Southern and Eastern Europe, Southern Australia, Northern and Southern Africa, and Russia. Between 2000 and 2020, several of these regions experienced drought events with unprecedented intensities compared to the 1950-2000 period (Jain et al., 2015[17]) (Figure 2.3 d). OECD countries are not spared from these worsening drought conditions. In 27 of the 38 OECD member countries, at least 50% of the national territory has experienced an increase in drought frequency, while in 24 countries, at least 50% of the land has seen an increase in drought intensity (see Table A.A.1 in Annex A).
Change in the average number of drought events ((a) and (c)) and their intensity ((b) and (d)) in the period 2000-2020 compared to 1950-2000
How to read this figure: Graph (a) shows that South of France has experienced more than three time more drought events in the period 2000-2020 than in the period 1950-2000, while Northern Mexico experienced a decrease in the number of droughts over the same periods. Graph (b) shows that, in most of Northern Africa, the average intensity of all drought events (average SPEI values below -1) occurring during the period 2000-2020 was more than 50% more intense than the average of those occurring during the period 1950-2000. Graph (c) shows that Eastern interior Australia has experienced over three times more extreme drought events in the period 2000-2020 than in the period 1950-2000, while Indonesia experienced a decrease in the number of extreme droughts over the same periods. Graph (d) shows that, in most of Brazil, the most extreme event (event with the lowest SPEI value) during the period 2000-2020 was more than 50% more intense than the most severe event recorded during the period 1950-2000.
Note: Drought events are defined as years in which the average annual SPEI value falls below -1 (Jain et al., 2015[17]). Drought frequency (a and c) is calculated as the number of drought events occurring at each location during the two periods, divided by the duration (in years) of each period. Drought intensity (b) represents the average SPEI value of drought events at each location for each period. Panel (d) shows the change in the maximum intensity of extreme drought events, calculated as the ratio of the lowest SPEI value during 2000-2020 to the lowest SPEI value during 1950-2000 at each location. A drought year is considered as extreme if the annual SPEI value is below or equal to -2, based on the drought severity classification from Jain et al. (2015[17]).
Source: Author’s own, based on data from Copernicus Climate Change Service (2022[19]).
2.2.3. Observed trends in freshwater availability
The primary concern related to droughts lies in their impacts on freshwater availability, as most of the economic, environmental and social impacts of drought are linked to freshwater scarcity (see Chapter 3). This section examines trends in freshwater quantity across major surface and groundwater reservoirs – including soils, rivers, glaciers, and aquifers – as well as the impacts of drought on freshwater quality.
Trends in soil moisture
Decreasing levels of soil moisture due to drought have become a critical concern, with agricultural drought conditions affecting one-third of the global land area between 1980 and 2023. During this period, 37% of the world's soils experienced significant drying, while less than 6% of the global land surface saw a significant increase in average soil water content (Figure 2.4). Among OECD countries, over half reported that at least 20% of their territory experienced significantly drier soils over the same period. In contrast, only ten OECD countries experienced an overall increase in soil moisture. In particular, Figure 2.4 shows that Colombia, Estonia, France, Korea, Latvia, Lithuania, Luxembourg, and Mexico were particularly affected by decreasing soil moisture, with more than 60% of their land experiencing significant soil drying over the last forty years. It is important to note, however, that these annual averages can mask substantial seasonal fluctuations, which may be even more severe and concerning, especially when drying trends are observed during the growing season (see Chapter 3).
Percentage of land area that experienced significant change in average soil moisture over the period 1980-2023
Note: The direction and statistical significance of changes in soil moisture are determined using a linear regression analysis, where annual average soil moisture (dependent variable) is regressed on the year (independent variable) for each location over the period 1980-2023. Statistical significance is assessed at a 10% level (p < 0.1). The percentage of a country's surface area experiencing significantly drier or wetter conditions is calculated as the ratio of grid cells (0.1° x 0.1° resolution) within the country showing a significant decrease or increase in average annual soil moisture to the total number of grid cells in that country.
Source: Author’s own, based on data from Copernicus Climate Change Service (2022[19]).
Trends in river flows
Decreasing average river flows have been observed in many regions of the world in recent decades. An analysis of global river streamflow trends shows that most rivers in Southern Europe, South Africa, Southern New Zealand, and Southern and Eastern Australia experienced decreases in average streamflow between 1951 and 2010 (Gudmundsson et al., 2019[20]; Amirthanathan, 2023[21]; Zhang, 2016[22]). In particular, 90% of rivers in Europe’s Mediterranean region experienced declining average stream flows between 1950 and 2013 (Masseroni et al., 2021[23]), driven by climate change, revegetation, and increased water extraction for irrigation (Vicente‐Serrano et al., 2019[24]). Recent data from over 1 000 river flow monitoring stations in Australia confirm these trends, with an increase in the annual average number of low-flow days – defined as daily flow below the 5th percentile of the monitored period – between 1980-2000 and 2000-2020 (Figure 2.5).
Average annual number of low-flow days across 1 174 river monitoring stations between the periods 1980-2000 and 2000-2020
Note: Low-flow days are defined as days on which the average daily river flow is below the 5th percentile of the mean daily flow recorded at a given station over its entire monitoring period. The monitoring period varies by station but includes at least the period 1980-2020. Only river stations with fewer than five missing values for both the 1980-2000 and 2000-2020 periods are included in this analysis.
Source: Author’s own, based on data from Chen et al. (2023[25]).
Trends in groundwater levels
The majority of monitored groundwater table levels have also shown widespread declines in recent decades. A recent analysis of aquifers that supply over 75% of global water withdrawals found that 62% of monitored stations reported declining average water levels between 2000 and 2020. This decline is even more pronounced in non-OECD countries, where 73% of monitored stations recorded declining water levels, compared to 60% in OECD countries. In addition, 30% of these global monitored aquifers experienced faster declines in water levels during 2000-2020 compared to earlier periods (Jasechko et al., 2024[26]). However, these trends vary regionally within each country. For example, while most of the monitored stations in Florida indicated groundwater replenishment between 2000 and 2020, the majority of stations in Northern Texas, California, and Kansas showed consistent declines in water levels (Figure 2.6).
Note: Each dot represents a single groundwater monitoring station. Alaska and Hawaii are excluded from the analysis.
Source: Author’s own, based on data from Jasechko et al. (2024[26]).
Trends in glacier depletion
Glacier depletion has significantly accelerated, with rising local temperatures and reduced snowfall driving faster melting and reducing annual replenishment. Between 2000 and 2020, glacier melt rates doubled, leading to widespread glacier retreat and threatening long-term water supply for many regions, as glaciers store around 70% of Earth’s freshwater (Hugonnet et al., 2021[27]; Li et al., 2022[28]; Bhattacharya et al., 2021[29]). This accelerated melting has temporarily alleviated declines in river and groundwater levels in some drought-affected regions. For example, between 2010 and 2020, glacier melt in the Argentinian and Chilean Andes contributed up to 8% of local river flows during the driest months, partially offsetting the effects of the "megadrought" that has affected the region since 2010 (Dussaillant et al., 2019[30]). However, this mitigation is unlikely to continue, given the rapid and ongoing loss of glacier mass (see Section 2.3.1).
2.2.4. Observed trends in compound and consecutive climate events
The observed increase in duration and frequency of extreme climate events amplifies the likelihood of droughts occurring concurrently or in succession with other extreme events. Globally, compound and consecutive weather events, such as heatwaves and droughts, have already become more common due to climate change, and this risk will continue to rise in the future as climate change intensifies (IPCC, 2023[31]).
Droughts can increase the likelihood and intensity of floods, particularly when dry conditions reduce soil absorption capacity. The occurrence of successive flood and drought events has increased in recent decades (Matano et al., 2023[32]). Prolonged droughts cause soil contraction, reducing water infiltration and increasing runoff (Matanó et al., 2024[33]), which can trigger landslides and flash floods when heavy rainfall occurs (Robinson, Vahedifard and AghaKouchak, 2017[34]). This is illustrated by the trends observed between 1980 and 2015, with 24% of global floods occurring during or immediately after drought periods (Matanó et al., 2024[33]). This pattern is particularly evident in South Africa and Mozambique, where river floods have been strongly correlated with preceding prolonged drought conditions (Franchi et al., 2024[35]).
Increasing drought severity and duration also heighten global wildfire risk. Droughts are a primary driver of extreme wildfires (OECD, 2023[36]), as demonstrated in studies linking droughts to large-scale fires in Türkiye and Mexico (Ertugrul et al., 2021[37]; Marín et al., 2018[38]). Some of the most devastating wildfires in recent history – including the 2018 Camp Fire in the United States (Hawkins et al., 2022[39]), the 2017 wildfires in Portugal and Chile (OECD, 2023[36]), and the 2020 wildfires in Arctic Siberia (Ciavarella et al., 2021[40]) – were fuelled by exceptionally dry conditions. In turn, forests exposed to wildfires become more susceptible to subsequent drought, raising concerns about their long-term sustainability in a changing climate. For example, forests affected by extreme wildfires tend to lose their ability to retain water, which makes them more sensitive to water shortages than mature forests (OECD, 2023[36]; Le Roux et al., 2022[41]).
Finally, climate change is set to drastically increase the frequency of compound drought and heatwave events. Low soil moisture exacerbates heatwaves through land-atmosphere feedback mechanisms, creating a self-reinforcing cycle of drought and extreme heat (Matanó et al., 2024[33]). The global frequency of these compound drought and heatwave events may increase tenfold by the end of the century (Yin et al., 2023[42]). The concurrence of these events is also particularly concerning as heatwaves significantly escalate water consumption, further compounding water scarcity issues (Cárdenas Belleza, Bierkens and van Vliet, 2023[43]).
While droughts are natural phenomena driven by natural weather and climate variations, recent trends indicate they are increasingly driven by climate change and other anthropogenic factors. This section examines how shifting precipitation patterns, rising temperatures, and other non-climatic drivers have shaped and will continue to shape the occurrence and intensity of drought events.
2.3.1. Climatic drivers of drought
Climate change amplifies drought risk through various interconnected drivers, including altered precipitation patterns and rising temperatures. A growing body of research increasingly provides evidence linking climate change to the intensification and frequency of drought events, quantifying how much more likely they become due to human-induced warming. For example, the 2022 droughts in the northern hemisphere were five to twenty times more likely and the ongoing drought in eastern Africa at least one hundred times more likely because of climate change (Schumacher, 2022[44]; Kimutai, 2023[45]).
Changing precipitation patterns
Climate change primarily influences drought occurrence by increasing annual and seasonal precipitation variability, which can lead to precipitation deficits in some regions. Since 1950, the inter-annual variability of average inland precipitation has increased considerably. Between 1950 and 2020, global maximum and minimum annual precipitation levels exceeded those recorded between 1900 and 1950 by a factor of six and five respectively, with extreme values up to three times higher (or lower) than those observed in the first half of the 20th century (Figure 2.8 a). There is broad scientific consensus that climate change has also altered interannual precipitation patterns. For example, France and Germany have experienced up to a 30% increase in average winter precipitation since pre-industrial times, coupled with an average 10% decrease in summer rainfall. Australia, on the other hand, has experienced reduced winter precipitation and increased summer rainfall (IPCC, 2022[46]).
Extreme precipitation patterns, driven by climate change, are also worsening drought risk. Heavy rainfall following prolonged dry periods can prevent effective water infiltration into the soil, worsening both agricultural and hydrological drought risks. Torrential rains, particularly on bare or compacted soils, can form a hard crust on the soil surface, leading to excessive runoff and preventing water infiltration into the soil. This process can reduce groundwater storage, soil moisture, and overall water availability (Eekhout et al., 2018[47]). As a result, even in areas experiencing episodic increases in precipitation, water availability may continue to decline.
Changes in precipitation patterns are not evenly distributed across the globe. While average global precipitation increased between 2000 and 2022 compared to 1950-2000, many areas experienced significant decreases in rainfall. For example, regions such as the Mediterranean, the Western United States, parts of South America, most of the African continent, the Middle East, and Eastern Australia all saw up to a 20% reduction in annual average precipitation during the period 2000-2020 compared to the previous fifty years (Figure 2.7).
Change in average annual precipitation (mm/year) between the periods 1950-2000 and 2000-2020
Source: Author’s own, based on data from Copernicus Climate Change Service (2022[19]).
Additionally, extreme precipitation deficits2 are also becoming more frequent in many regions due to climate change. Between 2000 and 2020, about 20% of global land experienced at least twice as many extreme annual precipitation deficit events compared to the previous fifty years (Figure 2.9). Combined with widespread increases in extreme temperatures, this trend has made regions such as South America, the western United States, northern East Africa, the Mediterranean, eastern Russia and eastern Australia particularly prone to drought.
As illustrated in Figure 2.1, reduced precipitation leads to declines in river flow, soil moisture, and aquifer recharge (Taylor et al., 2012[48]). Between 2000 and 2020, precipitation deficits alone accounted for 25% of flash agricultural drought (Zeng et al., 2023[49]). Similarly, 80% of aquifers with declining water levels over the same period were linked to below-average precipitation (Jasechko et al., 2024[26]).
Beyond total rainfall amounts, the timing of precipitation is equally critical in defining drought risk. For example, winter precipitation plays a crucial role in aquifer recharge, as less abundant vegetation allows for more water to infiltrate the ground. Conversely, reduced winter precipitation limits snowpack storage in mountainous regions, increasing summer drought risk by reducing available meltwater (Han et al., 2024[50]).
Rising atmospheric temperatures
The increase in global temperatures due to climate change is a key driver of higher evaporation rates, i.e. the transfer of liquid water from soil, rivers, and lakes into the atmosphere, which in turn amplify drought risk. Globally, continental surface temperatures have risen steadily since 1965, reaching an average of 1.8°C above pre-industrial levels by 2023 (IPCC, 2022[51]) (Figure 2.8 b). This warming trend is closely linked to the rising evaporation rates observed between 1980 and 2020 (Figure 2.8 b). In particular, heatwaves are an increasingly significant driver of flash droughts – i.e. a rapid-onset drought that develops over a short period –, with abnormally high temperatures having caused 50% more drought events during 2000-2020 compared to 1981-2000 (Zeng et al., 2023[49]). The effect of rising atmospheric temperatures is further compounded by solar radiation as well as wind, which further accelerates this process by disrupting the balance between atmospheric humidity and surface water (Vicente‐Serrano et al., 2019[52]).
Note: The precipitation anomaly is calculated as the difference between total annual precipitation and the average annual precipitation for the period 1901-2000. The temperature anomaly is calculated as the difference between the global inland average annual temperature and the global inland average temperature of pre-industrial times (1980-1900). Annual temperature anomalies are derived from the average of four datasets: Berkeley Earth, GISTEMPv4 (NASA), HadCRUT5 (Met Office Hadley Centre), and NOAAGlobalTemp v6.0 (NOAA). Annual potential evaporation values represent the global inland average evaporation, calculated at a 0.1° x 0.1° resolution. Potential evaporation refers to the maximum amount of water that could evaporate from a given surface (e.g. soil, rivers, lakes) assuming an unlimited supply of water.
Source: Author’s own, based on data from Blunden, Boyer and Bartow-Gillies (2023[53]) (Precipitation); (Rohde and Hausfather, 2020[54]; Lenssen et al., 2019[55]; Morice et al., 2021[56]; Huang et al., 2024[57]) (Temperature); (Copernicus Climate Change Service, 2022[19]) (Potential evaporation).
In parallel, rising atmospheric temperatures affect plant transpiration, i.e. the release of water vapour from plants during photosynthesis. Transpiration rates depend on atmospheric temperature, as well as on vegetation type and atmospheric gas concentrations, particularly carbon dioxide (CO2) and ozone. Higher CO2 concentrations affect plant photosynthesis by reducing stomatal openings and increasing leaf surface area, which can alter evapotranspiration rates (Skinner et al., 2017[58]; Swann et al., 2016[59]). Similarly, higher ozone concentrations can reduce plant transpiration, potentially mitigating drought risk (Arnold et al., 2018[60]).
Rising temperatures under climate change also disrupt the balance between solid and liquid freshwater, affecting both seasonal and long-term water availability. In mountainous regions, warmer temperatures reduce snowfall, increasing the proportion of rainfall and thus causing earlier snowmelt. This shift can deplete water reserves, leading to reduced water supplies during drier periods. In addition, global warming accelerates glacier melt and retreat. This poses a long-term threat to freshwater availability, as it reduces the ability of glaciers to sustain river flows and water supplies over time.
Change in the frequency of extreme annual precipitation deficit (a) and extremely hot year occurrence (b) between the period 2000-2020 and 1950-2000
How to read this figure: Graph (a) shows that the Western United States experienced two to more than three times as many extreme precipitation deficit events on average during 2000-2020 compared to 1950-2000. In contrast, the United Kingdom saw a decline in the average number of extreme precipitation deficit episodes over the same period. Graph (b) shows that the global average number of extremely hot years more than tripled during 2000-2000 compared to1950-2000, except in some areas of South America, Australia, India, Mozambique, Botswana, and Zimbabwe.
Note: (a) A year is considered as experiencing an extreme precipitation deficit if its total annual precipitation falls below the 10th percentile of the annual precipitation distribution for that location during the 1950-2000 period. (b) A year is considered as extremely warm if its annual average temperature exceeds the 90th percentile of the annual average temperature distribution for that location during the 1950–2000 period.
Source: Author’s own, based on data from Copernicus Climate Change Service (2022[19]).
2.3.2. Anthropogenic (non-climatic) drivers of drought
In addition to climate change, human activities such as water withdrawal and land-use changes are other key drivers of growing drought risk. This section explores how growing volumes of water withdrawals – primarily for irrigation – and large-scale changes in land use due to deforestation, agricultural practices, and urbanisation – have exacerbated drought conditions in many regions and are expected to continue doing so in the future (Figure 2.10).
How to read this figure: The blue arrows represent water flows, with the direction of the arrow indicating the flow direction. The ‘+’ and ‘-’ symbols show the effects of specific activities or phenomena (shown in black) on water availability at the source. For example, evapotranspiration from forests contributes to cloud formation over land, so afforestation increases evapotranspiration and cloud formation, while deforestation reduces water flow to the atmosphere. Similarly, precipitation enhances soil moisture, replenishes groundwater and raises surface water levels, while water abstraction for industrial and domestic purposes reduces both surface and groundwater levels.
Source: Author’s own.
Water withdrawals
Water withdrawals significantly influence the occurrence and severity of drought events. By extracting water from surface and underground reserves, water withdrawals slow the replenishment of water bodies and reduce the availability of water during dry periods. Water extraction for irrigation plays a particularly large role in amplifying the severity and duration of drought, due to the large volumes usually extracted.3 According to recent estimates, water pumping makes river droughts up to thirty times more severe and extends drought duration by ten times (Van Loon et al., 2022[61]; Ketchum et al., 2023[62]). Global expansion of irrigation in areas of high agricultural intensity explains much of the observed changes in groundwater levels (Scanlon et al., 2023[63]). For example, the shift from surface to groundwater irrigation in the High Plains region of the United States has been associated with significant declines in aquifer levels (Scanlon et al., 2021[64]).
Growing water withdrawals are closely linked to the expansion of irrigated agriculture as well as to climate change. Between 2001 and 2020, the surface of irrigated areas in OECD countries grew by 4% (Figure 2.11). This, together with the growing need for irrigation due increasingly dry conditions in many regions, has led to a 20% rise in water withdrawals for agricultural purposes (Figure 2.11).
Relative change in the total area of agricultural land equipped for irrigation (solid brown line) and total agriculture water withdrawal (blue dotted line) in OECD countries (2001-2020)
Note: Ireland and Luxembourg are not covered in this analysis due to their very limited area of irrigated land.
Source: Author’s own, based on data from FAO (2024[65]) (Surface of irrigation-equipped land) and FAO (2024[66]) (Total agriculture water withdrawal).
Excessive water abstraction for irrigation also degrades water quality, making drought episodes even more severe. Many aquifers and rivers worldwide have experienced higher salinity and pollutant concentrations during drought, partly due to increased water use for irrigation. For example, nitrate concentrations in California's Central Valley’s monitored wells exceeded regulatory thresholds four to five times more frequently during drought periods, due to increased water pumping for agricultural purposes (Levy et al., 2021[67]). Similarly, water withdrawals for irrigation during the Millennium Drought in Australia (1997-2009) and the 2000-2001 and 2007-2009 droughts in Florida exacerbated water salinity- reaching record levels that exceeded regulatory thresholds – threatening water use for irrigation and drinking supplies for millions of people (Murray–Darling Basin Authority, 2023[68]; Haque, 2023[69]).
Water withdrawal is expected to increase in the future, further exacerbating drought conditions. By the middle of the century, global water withdrawal volumes are projected to increase by 20-30% compared to 2020 (Boretti and Rosa, 2019[70]). These trends will be driven by increased water demand in key sectors (e.g. water use in the manufacturing sector is projected to grow by 400% by 2050 (Boretti and Rosa, 2019[70])) as well as by rising temperatures and worsening droughts and heatwaves under climate change, which are likely to increase water demand for irrigation, energy production, and other uses (Labbe et al 2023; Wang et al 2016). Under a high-emission scenario (RCP 8.5), water demand for irrigation is projected to increase sharply in many dry regions, for example in the Pacific Southwest of the United States (Warziniack et al., 2022[71]). At the same time, in some European areas, drinking water consumption may increase by up to 10% on hot days (Fiorillo et al., 2021[72]; Dimkić, 2020[73]).
Land-use and land-cover changes
Land-cover changes such as deforestation are key factors contributing to drought occurrence. Forest and vegetation dynamics play a significant role in shaping the water cycle, affecting precipitation and runoff patterns at both the local and global level. For example, deforestation reduces evapotranspiration and – when performed on a large scale – can inhibit cloud cover, reducing precipitation and thus exacerbating drought conditions (The Global Commission on the Economics of Water, 2023[74]; Perugini et al., 2017[75]; Smith, Baker and Spracklen, 2023[76]). In the Amazon rainforest, deforestation has been associated with 4% of the increase in drought intensity observed between 2001 and 2014 (Staal et al., 2020[77]). Overall, a 1% reduction in tropical forest area is estimated to reduce rainfall by about 0.25 millimetres per month within a 200 kilometre radius around the deforested area (Smith, Baker and Spracklen, 2023[76]). Conversely, reforesting 14% of Europe’s surface could lead to an 8% increase in average annual precipitation (Baker, 2021[78]; Meier et al., 2021[79]). However, when not carefully planned, afforestation can sometimes exacerbate local drought risk by reducing surface runoff and decreasing river flow downstream. For instance, intensive afforestation in the Pyrenees is estimated to reduce river streamflow by up to 50% during dry periods (Vicente‐Serrano et al., 2021[80]).
In some agricultural areas, unsustainable agricultural practices have also diminished soil water infiltration and retention capacity, exacerbating drought risk. For example, the expansion of water-intensive crops, such as maize, have contributed to major declines in soil moisture in areas like Northern China (Liu et al., 2015[81]). Similarly, the continued use of traditional tillage practices has accelerated evapotranspiration and soil erosion, further affecting soil moisture. The use of heavy machinery has also been associated with reduced water infiltration and soil water retention capacity, with negative impacts on groundwater recharge (Chyba, 2014[82]; El-Beltagi et al., 2022[83]).
Finally, soil sealing driven by urbanisation and other land-use changes also contributes to worsening drought conditions. Throughout the 21st century, the pace of soil sealing has accelerated, with sealed surfaces increasing on average by 50% in OECD countries and nearly doubling globally (Figure 2.12). The surface area of inland waters, an important freshwater reservoir, also decreased in several OECD countries, such as Australia (-15%) and Belgium (-8%). During the same period, wetland areas in OECD countries declined by 18% on average, with losses peaking at 50% in Chile and between 20 to 30% in Canada, Mexico, and the United States4 (Figure 2.12). The loss of such critical ecosystems, coupled with the artificialisation of riverbanks, have been associated with reductions in groundwater recharge, in addition to other ecological impacts such as loss of biodiversity, disruption of natural habitats, and diminished carbon sequestration capacity.
Percentage change in land cover type between 2000 and 2020
Note: Iceland is excluded from the figure as the data show no change in land cover.
Source: Authors’ own, based on data from Tesnière, Maes and Haščič (2024[84]).
In the context of climate change, drought patterns will continue to evolve, affecting the frequency, duration, and severity of drought events. Rising temperatures and shifting precipitation trends will continue to disrupt soil moisture, groundwater levels, and river flows, with varying impacts across regions. At the same time, more people and land will be exposed to drought. Finally, climate change is projected to heighten the likelihood of compound and consecutive climate events, such as flash droughts and heatwaves. The following sections explore these evolving trends under different warming scenarios.
2.4.1. Growing drought frequency, duration, and intensity
The observed trends in rising atmospheric temperatures and shifting precipitation patterns due to climate change are expected to persist in the future. Global warming is projected to reach between 1.8°C and 4°C by 2100 compared to pre-industrial levels under low-emission (SSP1-2.6) and high-emission (SSP5-8.5) scenarios, respectively (IPCC, 2021[9]) (see Box 2.1 for more details on these scenarios). Global average precipitation is estimated to increase by 1-2% for every additional degree of global warming (Trenberth et al., 2007[85]). However, these changes are projected to vary significantly across regions. Most notably, areas such as Latin America, the Mediterranean, Southern Africa, the Middle East, parts of Australia, and China are projected to experience notable decreases in average annual rainfall by 2050 and 2100 (Figure 2.13). Additionally, parts of South America, the Mediterranean, and Southern Africa could experience up to a fourfold increase in extreme low-rainfall episodes by the end of the century (compared to pre-industrial levels) across all climate scenarios (Cook et al., 2020[86]). At the same time, the frequency and intensity of extreme heat events is projected to rise sharply. By the end of the century, extreme heat events are projected to be 14 times more likely under a low-emission scenario (SSP1-2.6) and nearly 40 times more likely under a high-emission scenario (SSP3-7.0). The average intensity of these heatwaves could increase by up to 5°C compared to 1850-1900 levels (IPCC, 2021[9]).
Average annual precipitation anomaly (mm/year) and temperature anomaly (°C) for 2000, 2050, and 2100 under a moderate-emission scenario (SSP2-4.5), relative to the 1850–1949 baseline
Note: The values shown are the averages of the annual median gridded anomalies projected by the model ensemble for the periods 2000-2020 (2000), 2036-2064 (2050), and 2071-2099 (2100).
Source: Author’s own, based on data from Cook et al. (2020[86]).
To project future climate outcomes, the IPCC’s Sixth Assessment Report introduced five scenarios – known as SSP-RCP – that combine socioeconomic development pathways with different greenhouse gas concentration trajectories. These scenarios serve as inputs for the Sixth Coupled Model Intercomparison Project (CMIP6), which models future greenhouse gas emissions and associated climate change projections until 2100. The SSP-RCP framework combines two major scenario systems:
The Shared Socioeconomic Pathways (SSPs) outline five global development narratives (SSP1 to SSP5) based on different assumptions about economic development, population trends, technological advancement, education, and energy use. Each scenario is labelled SSPx-y, where “x” indicates the socioeconomic pathway and “y” the associated radiative forcing level (W/m²) by 2100, indicating the intensity of climate change under different emission mitigation scenarios.
This approach builds on the Representative Concentration Pathways (RCPs) used in the IPCC’s Fifth Assessment Report. RCPs are greenhouse gas concentration trajectories associated with specific radiative forcing levels. They range from strong mitigation scenarios (RCP2.6) to high-emissions (RCP8.5) pathways – reflecting a range of possible climate futures depending on the degree of global mitigation ambition.
Source: (Andrew, 2016[87]).
By linking socioeconomic narratives with emissions trajectories, the SSP-RCP framework helps capture how both human development patterns and mitigation efforts shape future drought exposure and severity. Future drought conditions are assessed using three of the five SSP-RCP scenarios. The “middle of the road” scenario (SSP2-4.5) serves as the baseline, while the “sustainability” scenario (SSP1.2-6) and the “regional rivalry” scenario (SSP3-7.0) provide lower and upper bounds of potential drought risk under different emission pathways.
Source: (IPCC, 2021[9]; Andrew, 2016[87]).
These shifts in precipitation patterns, combined with rising atmospheric temperatures, are expected to make droughts more frequent, prolonged, and intense in many regions. By the end of the century, global drought frequency could increase by 30%, with average drought intensity more than doubling under moderate- to high-emission scenarios (SSP2-4.5 and SSP3-7.0), compared to 1991-2014 (Figure 2.15). Global average drought duration is also projected to rise by 50% under SSP2-4.5 and by 130% under SSP3-7.0 by 2100, relative to the 1950-2000 period (Zhou et al., 2023[88]).
Note: The SPEI is used to assess projected change in average global drought frequency, duration, and intensity.
Source: (Zhou et al., 2023[88]).
Climate change is also projected to increase the frequency of extreme drought events, i.e. drought episodes characterised by exceptional intensity and duration. These shifts in the occurrence of extreme events will be more pronounced than changes in average drought conditions (IPCC, 2022[46]). For example, in Canada, the United States, and Mediterranean Europe, the frequency of extreme agricultural droughts is projected to double or triple under 2°C of warming (IPCC, 2022[46]). The share of global land and population exposed to extreme drought events is projected to increase from 3% today to 7% and 8%, respectively, by 2100 (Pokhrel et al., 2021[89]). Climate change may also increase the frequency of long, multi-year droughts5 up to fivefold (Wu et al., 2022[90]).
In addition, the increasing coincidence of heatwaves and extreme precipitation deficits is expected to intensify the risk of flash droughts. These events are particularly concerning because they develop suddenly and with limited warning, making them challenging to predict and mitigate. Based on trends from 2000-2020, the frequency of flash droughts is projected to rise by around 20% in Europe, Indonesia, and China, and up to 25% in Latin and North America by 2100 (compared to 2015) under a moderate-emission scenario SSP2-4.5 (Christian et al., 2023[91]).
As drought conditions worsen, both the human population and agricultural lands will face increasing exposure to average and extreme drought conditions. By 2050, more than 1.6 billion people – including nearly 20% of the African population – will be exposed to severe and extreme droughts (Thow et al., 2022[92]), with up to 700 million people potentially forced to migrate due to droughts by 2030 (UNCCD, 2022[93]). Under a 2°C warming scenario, the global population exposed to agricultural droughts every year will more than triple (Lange et al., 2020[94]). Additionally, by the end of the century, the annual area of agricultural land exposed to flash droughts may rise by 20% in North America and 30% in Europe under a moderate-warming scenario (SSP2-4.5) (Christian et al., 2023[91]).
Overall, climate change will exacerbate existing inequalities in drought exposure, intensifying drought risk in regions that are already severely affected. Drought hotspots identified in Section 2.2, such as the Mediterranean, Southern North America, Latin America, Southern Africa, and parts of Australia are projected to experience severe drought conditions more frequently by 2050 and 2100 under a moderate-emission scenario (SSP2-4.5) (Figure 2.16).
Average annual SPEI values for 2050 and 2100 under a moderate emission scenario (SSP2-4.5), relative to the 1995–2014 baseline
Note: The values shown in this figure represent the average of the median annual gridded SPEI values projected by the model ensemble for the periods 2036-2064 (2050) and 2071-2099 (2100).
Source: Author’s own, based on data from World Bank (2024[95]).
2.4.2. Projected impacts on soil moisture, groundwater levels, and river flows
Despite an expected increase in global average precipitation, agricultural droughts – driven by worsening soil moisture deficits – are projected to become significantly more severe (Figure 2.17). By the middle of the century nearly 70% of global land area could experience declining soil moisture under a moderate-emission scenario (SSP2-4.5), relative to pre-industrial levels under a SSP2-4.5 scenario. In addition to the drought hotspots identified in the previous paragraph, India, the United States, Europe, eastern Russia, and China are also projected to experience substantial reductions in soil moisture. Even in regions where meteorological droughts are projected to intensify, such as the Mediterranean and South America, drought impacts on agriculture may be even more severe due to rapid soil moisture depletion (Gimeno‐Sotelo et al., 2024[96]).
Average annual standardised surface soil moisture anomaly for 2000, 2050 and 2100, under a moderate emission scenario (SSP2-4.5), relative to the 1850–1949 baseline
Note: The figure shows surface soil moisture levels at a depth of 0-30 centimetre. The values shown are the averages of the annual median gridded anomalies projected by the model ensemble for the periods 2000-2020 (2000), 2036-2064 (2050) and 2071-2099 (2100).
Source: Author’s own, based on data from Cook et al. (2020[86]).
Under climate change, groundwater levels and river flows in many regions are also likely to decline, though projections remain uncertain due to varying water use and withdrawal trends. Most aquifers are projected to experience declining levels (Amanambu et al., 2020[97]), with depletion rates potentially doubling by 2100 compared to the early 21st-century trends (Wada, 2015[98]). Similarly, while future river flow projections vary across models, most models anticipate increases in river flow in Canada and Northern Europe and declines in the Mediterranean and Southern Africa (IPCC, 2022[46]).
While climate models indicate a clear trend of increasing drought risk, significant uncertainties remain. A key source of uncertainty is the substantial variability across models and emission scenarios (IPCC, 2023[99]). For example, soil moisture projections for 2050 and 2100 under SSP1-2.6 and SSP3-7.0 (Figure 2.18) show considerable regional variation. This highlights the complex interaction between climate change, local conditions, and water management policies. Additional sources of uncertainty arise from differences in the definitions and indicators used to assess drought, the limited historical data available for model calibration, and differing statistical methods used in model development (see (Gimeno‐Sotelo et al., 2024[96]) for a review), as well as future water management policies and practices.
Percentage change in average surface soil moisture by 2050 & 2100 under a low-emission scenario (SSP1-2.6) and a high-emission scenario (SSP3-7.0), compared to a moderate emission scenario (SSP2-4.5)
Note: The values shown are the ratio between the averages of the annual median gridded anomalies projected by the model ensemble for the periods 2036-2064 (2050) and 2071-2099 (2100) under SSP1-2.6 or SSP3-7.0 scenarios and SSP2-4.5.
Source: Author’s own, based on data from Cook et al. (2020[86]).
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← 1. Evapotranspiration refers to the combined loss of water that occurs through evaporation – i.e. the transfer of liquid water from soil, rivers, and lakes into the atmosphere – and the release of water vapour from plants.
← 2. In the context of this analysis, extreme precipitation deficits are defined as years when total annual precipitation falls below the 10th percentile of 1950-2000 levels.
← 3. Irrigation accounts for about 72% of the global volume of water withdrawals, followed by industry (16%) and domestic and municipal uses (13%) (United Nations, 2024[100]).
← 4. Changes in wetland surface should be interpreted with caution, as most of the observed loss corresponds to a conversion to forest land between these periods. In some cases, definitions of wetlands and forests overlap, making the distinction between them ambiguous.
← 5. Wu et al. (2022[90]) defines long, multi-year droughts as droughts that persist for more than ten years.