The western United States is in a period of extreme drought. California, Nevada, Oregon, Washington and Idaho all experienced unusually dry rainy seasons, with more than 44 million people in those five states experiencing drought.
The two largest U.S. reservoirs, Lake Mead and Lake Powell, are at record lows since they were first built 86 and 56 years ago, respectively, and drought conditions are expected to continue through much of the western U.S. for at least June.
Droughts and droughts are common in the West, but unprecedented in recent years. The ongoing megadrought in the Southwest (since 2000) is the worst in 1,200 years, and a recent study shows that without human-caused climate change, the intensity of the drought would have been reduced by 42%.
Unusual droughts and a warming climate put the West’s water resources and the people, ecosystems and food supplies that depend on it at risk.
Western water demand
The American West is a vast region with diverse water needs, including water supplies for rural communities, developing cities, tribal nations, and critical ecosystems, in addition to agricultural, industrial, and hydroelectric uses.
In the West, irrigation generates the largest water demand. The 17 western states account for 81 percent of the nation’s irrigation water use. California has the highest irrigation water needs of any state and supplies most of the country’s fruits, nuts and vegetables.
Not having enough water to meet these demands can have costly consequences. The 2021 drought will cost the California agriculture sector about $1.1 billion and nearly 8,750 jobs, according to preliminary estimates by UC Merced researchers.
Despite the water supply risks, the western states have the highest domestic water consumption per capita in the nation.
How can the West meet its water needs?
Snow accounts for more than 50 percent of the water supply throughout the western United States and more than 70 percent in the mountains.
The western mountains act as natural water tanks. Snow accumulates at high altitudes during the colder months and melts during the warmer months, flowing down to reservoirs, streams and groundwater aquifers, supporting the people, ecosystems and industries of the region.
But since the 1950s, the western region has seen less snow cover and less precipitation, such as snowfall. Warmer winters also lead to earlier melt, making it harder for the annual snowpack to last into the warmer seasons when water needs are at their peak.
These trends are likely to continue, with freshwater from snow projected to decline by a further 25% by 2050, putting pressure on another important regional water source: groundwater.
Groundwater is water found in cracks and pores in rocks and soil. Groundwater aquifers, recharged by rainfall and runoff, provide agricultural irrigation and drinking water for millions of people in the West.
But satellite data shows groundwater is depleting in the West, especially in agricultural regions like California’s Central Valley, where up to 40 percent of irrigation water comes from aquifers and now as many as one-fifth of groundwater wells are in the worst drought. dry up during the period.
Climate change plays a role in water stress in the West, and it’s likely to continue. Human-caused climate change and its impact on snowfall is responsible for a 30-50% drop in water flow in the Colorado River Basin in recent decades. Several consecutive years of snow droughts are expected to become more frequent in the coming decades, especially under high-emission scenarios.
Timing is everything for water in the West, and April 1st is key.
There is a mismatch between when snow packs and when snow source water is needed to meet major agricultural, ecological and public needs in the West.
Water managers track these seasonal cycles using the “water year,” a 12-month cycle that begins on October 1 each year as snow begins to accumulate. Snow scouting on April 1 (midway through the water year) is an important indicator of the year’s availability of water to meet peak warm season demand.
But since 1955, the availability of fresh snow source water on April 1 in the West has decreased by 15-30%. This is partly due to snow in April. But a broad shift to earlier peak snow also means that April 1 snow needs to be extended for a longer period of time during peak demand months.
The area’s water infrastructure, including dams and reservoirs, has supplied water for more than a century. But it was designed to manage and store a reliable amount of melt from spring and summer snowpack. Water management strategies in the West are adapting to low snow conditions as mountain snow packs decrease and melt times advance.
Weather resistant water supply
Maintaining a stable water supply in the West is becoming increasingly difficult due to climate change and increased demand for water. Existing approaches to reducing water stress on residents, ecosystems and industry include: