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For tens of millions of Americans, drought has become an ever-present natural disaster.

Events such as the moderate-to-extreme drought conditions that covered more than half of the mainland U.S. in 2012, the megadrought in the West that continues today, and summer 2021’s record-low water levels at Lake Mead have kept dry spells in the news spotlight and kept drought impacts – strict water conservation measures, crop failures, and fears that dried-up vegetation will spark dangerous wildfires – on people’s minds.

Drought conditions across the contiguous United States as of August 10, 2021. Around 40% of the U.S. is experiencing drought. (Source: U.S. Drought Monitor/Drought.gov)

That’s particularly true in the Western United States. Because of the West’s largely semi-arid and desert climates, droughts are natural occurrences across the region. However, regional climate isn’t the only culprit in drought activity. Climate change, namely rising average temperatures driven by human-generated emissions of heat-trapping greenhouse gases, is contributing to droughts, too.

Warmer temperatures lead to drying

Global warming increases the risk of drought in several ways.

For one, water generally evaporates more quickly at higher temperatures. For that reason, hotter weather can result in drier soils. As high air temperatures sap liquid water from soils and plant leaves, transforming it into atmospheric water vapor via a process called transpiration, ground-level drying will increase in some regions. (Ironically, this additional atmospheric moisture triggers heavier downpours in other regions, which explains why the overall trend in the U.S. has been toward wetter conditions.)

Higher air temperatures not only encourage drought conditions to build but also intensify them. What might have otherwise been a mild or moderate drought in a cooler world will become, in a warmer world, more severe as a result of increased evaporation.

Warming also diminishes snowfall, an essential water resource for the estimated 1.9 billion residents of the Northern Hemisphere who depend on snowpacks, or snow reservoirs that store water during the cooler months and release it when it’s needed in the warmer, drier months. Rising temperatures increase the fraction of winter precipitation that falls as rain rather than snow and also shorten the cold season, so there’s less time for snow to even occur. Such was the case in 2015, the fourth-warmest year in the contiguous U.S., when a snow drought reduced the April snowpack in the Sierra Nevada mountain range to a mere 5% of its historical average water content — its lowest snowpack in 500 years.

The percent chance that the historical average (1865-2016) elevation of snowpack in each Sierra Nevada subregion will retreat given a 1 C (1.8 F) increase in average winter air temperature. (Source: NOAA Climate.gov/Fiona Martin)

Seasonal melting of snowpacks can be thrown off-kilter, too. As average temperatures warm above freezing earlier in the spring, snowmelt occurs sooner and faster than usual. And rapid melting results in a shorter period during which soils and plants are kept moist.

Another way a warmer atmosphere can disrupt precipitation is by shifting storm tracks. Ordinarily, low-pressure systems known as extratropical cyclones form between 30 and 60 degrees latitude north and south of the equator. But as the climate warms globally, storms are shifting toward the poles. This means that weather features such as atmospheric rivers, which supply as much as 50% of annual precipitation to states in the Western U.S., could cease to pass over regions where their moisture is much-needed.

Is global warming causing more droughts?

Scientists see a clear correlation between droughts and global warming. But a correlation between two events doesn’t always mean one caused the other. For example, ice cream sales often increase around the time that baseball game attendance rises, but that does not mean that eating ice cream causes people to attend baseball games. Nor does it mean that attending baseball games causes people to eat ice cream.

It can be tricky to attribute an increase in droughts to global warming because droughts are variable. In other words, they can occur every year or every few years, last for years or decades, and cause varying levels of dryness. That makes it difficult to distinguish random events from those possibly shaped by human-caused warming. However, the more drought dovetails with trends of increasing temperature, decreasing precipitation, and with computer model projections, the more confident scientists are in pointing to climate change.

In a 2020 study in the journal Science, for example, researchers observed how human-caused climate change is contributing to the 21st-century megadrought in the Western U.S. and northern Mexico by evaluating trends in modeled temperature, relative humidity, and precipitation data between 1901 and 2018. According to the study’s findings, human-caused warming accounts for 46% of this drought’s severity.

What about the rest of the world? Scientists have been cautious about linking human activities to global drought patterns, largely because drought hasn’t occurred as uniformly worldwide as it has across individual regions. That said, building evidence supports the climate change-drought connection on a global scale.

According to an August 2021 report by the Intergovernmental Panel on Climate Change, scientists have high confidence that for every half degree Celsius (0.9 degree Fahrenheit) the atmosphere warms, noticeable increases will occur in some regions in the intensity and frequency of droughts that harm agriculture and ecosystems. Similarly, the report notes that extreme agricultural and ecological drought events that used to occur once every 10 years are now 1.7 times more likely than they were from 1850 to 1900, before humans heavily influenced the climate.

How drought-prone communities can endure future dry spells 

While the intricacies of the climate change-drought connection are still being uncovered, scientists tend to agree on one thing: Droughts will likely become more intense into the 2050s and beyond. The likelihood of megadroughts – droughts lasting 10 years or more – is also projected to increase from its current 12% to more than 60%, a NASA study warns.

A conservation mindset is one of the best defenses against drought and its associated risks of wildfire, crop failure, energy crises, and more. Whether you’re preparing for a drought or are already experiencing one, strengthen your resilience by taking these actions:

  • Become drought-aware. Keep up with current drought conditions by visiting the National Integrated Drought Information System, and use the Drought Risk Atlas to explore how susceptible your region is to drought.
  • Xeriscape lawns and city green spaces. Replacing traditional lawn vegetation with native, drought-tolerant plants reduces a home’s outdoor water demand by 50-70%, according to National Geographic. 
  • Repair leaky indoor and outdoor faucets. A seemingly small leak that drips once per second can waste 2,700 gallons of water a year, according to the American Red Cross.  
  • Install green infrastructure. Green streets, green roofs, and porous pavements allow whatever rain that does fall to slowly soak into the ground and replenish local groundwater reserves rather than be lost to storm drains.
  • Improve your home’s energy efficiency. Since water is needed to generate hydroelectric power and for cooling in other types of energy production, power grids can easily become strained during droughts. Taking care to fully load dishwashers and washing machines, use “light wash” settings, and limit power consumption during peak times (4 p.m. to 9 p.m. local time) can help your community avoid preemptive power shutoffs, or worse, blackouts.
  • Build an emergency water supply in your pantry. The CDC recommends storing at least one gallon of water per person per day (half a gallon for drinking; half for personal use). Visit their website for tips on how to safely store drinking water.

Although drought is an immense concern now and in the future, taking small actions such as these can have cascading benefits.

Tiffany Means is a science writer based in the Blue Ridge mountains of North Carolina. Before becoming a writer, she was a meteorologist. Her stories distill science news and concepts in a relatable… More by Tiffany Means

Edited by veteran journalist and journalism educator Bud Ward, Yale Climate Connections is a nonpartisan, multimedia service providing daily broadcast radio programming and original web-based reporting, commentary, and analysis on the issue of climate change, one of the greatest challenges and stories confronting modern society. www.YaleClimateConnections.org