Background on Drought
A drought is “a deficiency of precipitation over an extended period of time (usually a season or more), resulting in a water shortage.” Indicators of drought include precipitation, temperature, streamflow, ground and reservoir water levels, soil moisture, and snowpack.
Drought and Climate Change
Climate change increases the odds of worsening drought in many parts of the United States and the world. Regions such as the U.S. Southwest, where droughts are expected to get more frequent, intense, and longer lasting, are at particular risk.
How climate change contributes to drought:
- Warmer temperatures enhance evaporation, which reduces surface water and dries out soils and vegetation. This makes periods with low precipitation drier than they would be in cooler conditions.
- Climate change is also altering the timing of water availability.
- Warmer winter temperatures are causing less precipitation to fall as snow in the Northern Hemisphere, including in key regions like the Sierra Nevada of California.
- Decreased snowpack can be a problem, even if the total annual precipitation remains the same. This is because many water management systems rely on spring snowpack melt . Likewise, certain ecosystems also depend on snowmelt, which supplies cold water for species like salmon. Because snow acts as a reflective surface, decreasing snow area also increases surface temperatures, further exacerbating drought.
- Some climate models find that warming increases precipitation variability, meaning there will be more periods of both extreme precipitation and drought. This creates the need for expanded water storage during drought years and increased risk of flooding and dam failure during periods of extreme precipitation.
- Climate change is making certain regions drier
- For example, the Southwestern United States has already seen a decrease in annual precipitation since the beginning of the 20th century, and that trend is expected to continue.
- Estimates of future changes in seasonal or annual precipitation in a particular location are less certain than estimates of future warming, and are active areas of research. However, at the global scale, scientists are confident that relatively wet places, such as the tropics and higher latitudes, will get wetter, while relatively dry places in the subtropics (where most of the world’s deserts are located) will become drier.
- In some areas, droughts can persist through a vicious cycle, in which very dry soils and diminished plant cover absorb more solar radiation and heat up, encouraging the formation of high pressure systems that further suppress rainfall, leading an already dry area to become even drier.
Recent U.S. droughts have been the most expansive in decades. At the peak of the 2012 drought, the most extensive drought since the 1930s, an astounding 81 percent of the contiguous United States was under at least abnormally dry conditions.
California experienced a particularly drawn-out drought from December 2011 to March 2019, broken in part by the wettest winter in the United States. 2020 saw widespread, prolonged drought that was exacerbated by heat waves in more than a dozen Western and Central states. The intense drought and heat combined to wither vegetation, intensifying Western wildfires that burned record acreage.
Nationwide, conditions reached their peak in December 2020, when the greatest extent of land since 2012 was under extreme drought conditions. In the West, drought has continued and intensified in 2021, and has been exacerbated in the Pacific Northwest by record heat.
Threats Posed by Drought
The United States is historically susceptible to drought. Paleoclimate studies show major droughts in the distant past, with more recent dry periods still within living memory, such as the Dust Bowl of the 1930s or the drought of the 1950s. These historic examples serve as guideposts to highlight our vulnerabilities to drought as we move into a warmer and, in some places, drier future.
Severe drought can affect:
- Water supply: Droughts are defined by their lack of available water. During droughts, communities may have limited access to water for household use, including drinking, cooking, cleaning, and watering plants, as well as for agriculture, transportation, and power generation. Droughts may lead to higher water costs, rationing, or even the decimation of important water sources like wells, as a drought did in a rural California community in 2021.
- Agriculture: Droughts affect livestock and crops, including corn, soybeans, and wheat. At the height of the 2012 drought, the U.S. Department of Agriculture declared a natural disaster over 2,245 counties, 71 percent of the United States. Globally, drought struck several major breadbasket regions simultaneously in 2012, adding to food price instability. In countries already facing food insecurity, cost spikes can lead to social unrest, migration, and famine.
- Transportation: Droughts can lower river water levels, threatening commerce on rivers like the Mississippi. Transport barges need at least nine feet of water to operate, and to maintain this level, the U.S. Army Corps of Engineers had to blast, dredge, and clear obstructions on a key stretch of the Mississippi in 2013. Drought is also often accompanied by extreme heat, which can buckle roadways, ground planes, and warp public transit cables. Drought-fueled wildfires also have repercussions for travel by closing roadways and railroads and grounding planes when smoke is thick.
- Energy: Droughts can raise concerns about the reliability of electricity production from plants that require cooling water to maintain safe operations. Hydroelectric power may also become unavailable during droughts. When heat waves coincide with droughts, electricity demands can grow, compounding stress on the grid.
- Public Health: Reduced flows in rivers and streams can concentrate pollutants, threatening the quality of water used for drinking and recreation. Also, drought-fueled wildfires can expose nearby communities to smoke and pollutants, which can exacerbate chronic respiratory illnesses.
All of these drought impacts can inflict extreme costs on people, businesses, and governments. From 2011 through 2020, the United States experienced nine droughts, each causing at least $1 billion in damages.
Droughts also increase the amount of carbon dioxide in the atmosphere, including by decreasing which reduces the amount of vegetation storing carbon dioxide. In addition, increases in drought-related wildfire and soil erosion can release carbon dioxide sequestered in trees and plants back into the atmosphere.
How to Build Resilience
Governments and businesses must identify their vulnerability to drought and improve resilience. They can help prepare for both future droughts and climate change by practicing and promoting water conservation and enhancing water efficiency throughout landscapes, city plans, and water infrastructure. They can also identify alternative water supplies, create drought emergency plans, and encourage farmers to plant drought-resistant crops.
The Climate Mapping for Resilience and Adaptation portal helps communities understand and plan for their climate risks today and in the future, including a real-time map of wildfire, drought, flooding, and extreme heat across the United States.
Other actions that improve resilience to other stressors, like deploying green infrastructure for stormwater management increasing energy efficiency in buildings (thereby using less power from plants that rely on water to function), and using renewable energy like solar (that isn’t reliant on water) can improve resilience to drought as a co-benefit.
These steps will be most effective if they are combined with reductions in greenhouse gases that can minimize the ultimate magnitude of climate change. Luckily, many solutions that build resilience to drought and other climate stressors – like water conservation and improving soil health – can also reduce greenhouse gas emissions.