Drought and climate change

Top Line

Human-caused global warming is increasing drought risk across much of the United States as rising temperatures accelerate evaporation, increase water uptake by heat-parched plants, and reduce the amount of winter snowpack available to refresh regions during dry summer months.

Facts for Any Story

• There have always been droughts—temporary periods when the supply of moisture fails to meet human and environmental demands. But much of the U.S. West is now experiencing something different: a long-term drying, or “aridification,” driven primarily by rising temperatures and changing precipitation patterns that have their roots in human-caused global warming.¹Overpeck, J.T. and Udall, B. (2020), Climate change and the aridification of North America, Proceedings of the National Academy of Sciences, 117 (22) 11856-11858 View Source
• Droughts are increasing in frequency and intensity as climate change leads to more water-cycle extremes in which, for example, large amounts of rain fall all at once, followed by long periods of no rain at all.²Rhode, Melissa M. (2023), Floods and droughts are intensifying globally, Nature Water, 1 226-227 View Source³Rodell, Matthew and Li, Bailing (2023), Changing intensity of hydroclimatic extreme events revealed by GRACE and GRACE-FO, Nature Water, 1 241-248 View Source Other examples of water cycle changes include less snow and more rain in winter, earlier snowmelt and runoff leading to earlier green-up, and more plant water use because of longer, warmer growing seasons.
• Droughts are among the costliest weather and climate-related disasters in the United States, exceeded in costs only by hurricanes and severe storms over the past four decades.⁴NOAA National Centers for Environmental Information (2024), Billion-Dollar Weather and Climate Disasters: Summary Stats View Source
• Since the 1950s, climate change-fueled changes in the water cycle have caused droughts to develop faster, increasing the frequency of “flash droughts”—those that appear suddenly, with little warning. As increased heat drives evaporation, flash droughts rapidly reduce soil moisture, with potentially severe impacts on agriculture and ecosystems.⁵Yuan, Xing, et al. (2023), A global transition to flash droughts under climate change, Science, 380 (6641) 187-191 View Source⁶Walker, David W. and Van Loon, Anne F. (2023), Droughts are coming on faster, Science, 380 (6641) 130-132 View Source
• As temperatures go up, drought risk goes up, even in areas where rainfall has remained close to normal, because of increased evaporation and water uptake by plants. From 2000 to 2010, for example, high temperatures in the upper Missouri River Basin—the United States’ largest river basin—significantly contributed to a decade-long drought that by some measures (e.g., river-flow decline) was more severe than the Dust Bowl and could not be accounted for by the modest decreases in precipitation alone.⁷Martin, J.T., et al. (2020), Increased drought severity tracks warming in the United States’ largest river basin, Proceedings of the National Academy of Sciences, 117 (21) 11328-11336 View Source
• Warming has caused snowpack declines in many U.S. areas over recent decades, increasing drought risk, as the western United States relies heavily on snowmelt for water supply.⁸Gottlieb, Alexander R. and Mankin, Justin S. (2024), Evidence of human influence on Northern Hemisphere snow loss, Nature, 625, 293–300 View Source⁹Siirila-Woodburn, Erica R., et al. (2021), A low-to-no snow future and its impacts on water resources in the western United States, Nature Reviews Earth & Environment, 2, 800-819 View Source¹⁰Kampf, Stephanie K., et al. (2022), Increasing wildfire impacts on snowpack in the western U.S., Proceedings of the National Academy of Sciences, 119 (39) e2200333119 View Source Springtime heat waves, like those that drove record snow melt in the U.S. West in 2021, can hasten melting and intensify resulting droughts.¹¹McEvoy, Daniel J. and Hatchett, Benjamin J. (2023), Spring heat waves drive record western United States snow melt in 2021, Environmental Research Letters, 18 014007 View Source Dry air during heat waves can also increase sublimation, reducing runoff even in years with normal snowpack levels.
• Wildfires have increased in size and intensity in the western United States and the fire season has grown longer (see Quick Facts on Wildfires and Climate Change). Drought plays a role as it combines with hot, dry, and windy fire weather to increase wildfire risk—conditions that are increasing across the U.S. West. Human-caused global warming is likely to be the primary driver of these changes.¹²Richardson, Doug, et al. (2022), Global increase in wildfire potential from compound fire weather and drought, npj Climate and Atmospheric Science, 5, 23 View Source Wildfire increases, in turn, speed snowpack melt, and intensify drought in some areas.¹⁰Kampf, Stephanie K., et al. (2022), Increasing wildfire impacts on snowpack in the western U.S., Proceedings of the National Academy of Sciences, 119 (39) e2200333119 View Source
• Human-caused global warming was responsible for over 40% of the severity of the dry spell that parched the U.S. Southwest from 2000 to 2021, changing what would have been a moderately arid stretch into the driest 22-year period since at least the year 800.¹³Williams, A. Park, et al. (2022), Rapid intensification of the emerging southwestern North American megadrought in 2020–2021, Nature Climate Change, 12, 232–234 View Source
• Droughts reduce availability of water for hydropower generation and heat waves increase demand for electricity, causing greater dependence on fossil fuel-burning power plants and increasing air pollution. One simulation based on California data suggests that human health impacts would be highest in hot, dry years, with people of color disproportionately affected.¹⁴Zeighami, Amir, et al. (2023), U.S. West Coast droughts and heat waves exacerbate pollution inequality and can evade emission control policies, Nature Communications, 14, 1415 View Source
• Drought doesn’t just weaken and kill plants; it prevents new ones from growing. A decades-long period of hot and dry weather that affected many parts of the Rocky Mountains from the 1980s through about 2010 resulted in significant decreases in tree regeneration and forest resilience.¹⁵Davis, Kimberley T., et al. (2019), Wildfires and climate change push low-elevation forests across a critical climate threshold for tree regeneration, Proceedings of the National Academy of Sciences, 116 (13) 6193-6198 View Source

Pitfalls to Avoid

Don’t assume that drought is just about the amount of precipitation. Though it may seem counterintuitive, even places that see increases in precipitation can face a heightened drought risk because the temperature-related increase in evaporation and water demand by plants can outpace the increase in precipitation.