By Mojtaba Sadegh, Amir AghaKouchak, and John Abatzoglou
Just about every indicator of drought is flashing red across the western U.S. after a dry winter and warm early spring. The snowpack is at less than half of normal in much of the region. Reservoirs are being drawn down, river levels are dropping and soils are drying out.
It’s only May, and states are already considering water use restrictions to make the supply last longer. California’s governor declared a drought emergency in 41 of 58 counties. In Utah, irrigation water providers are increasing fines for overuse. Some Idaho ranchers are talking about selling off livestock because rivers and reservoirs they rely on are dangerously low and irrigation demand for farms is only just beginning.
Scientists are also closely watching the impact that the rapid warming and drying is having on trees, worried that water stress could lead to widespread tree deaths . Dead and drying vegetation means more fuel for what is already expected to be another dangerous fire season .
U.S. Interior Secretary Deb Haaland and Agriculture Secretary Tom Vilsack told reporters on May 13 that federal fire officials had warned them to prepare for an extremely active fire year . “We used to call it fire season, but wildland fires now extend throughout the entire year, burning hotter and growing more catastrophic in drier conditions due to climate change,” Vilsack said .
The many faces of drought
Several types of drought are converging in the West this year, and all are at or near record levels.
When too little rain and snow falls, it’s known as meteorological drought. In April, precipitation across large parts of the West was less than 10% of normal , and the lack of rain continued into May.
Rivers, lakes, streams and groundwater can get into what’s known as hydrological drought when their water levels fall. Many states are now warning about low streamflow after a winter with less-than-normal snowfall and warm spring temperatures in early 2021 speeding up melting. The U.S. Bureau of Reclamation said Lake Mead, a giant Colorado River reservoir that provides water for millions of people, is on pace to fall to levels in June that could trigger the first federal water shortage declaration , with water use restrictions across the region.
Dwindling soil moisture leads to another problem, known as agricultural drought. The average soil moisture levels in the western U.S. in April were at or near their lowest levels in over 120 years of observations .
These factors can all drive ecosystems beyond their thresholds – into a condition called ecological drought – and the results can be dangerous and costly. Fish hatcheries in Northern California have started trucking their salmon to the Pacific Ocean , rather than releasing them into rivers, because the river water is expected to be at historic low levels and too warm for young salmon to tolerate.
One of the West’s biggest water problems this year is the low snowpack.
The western U.S. is critically dependent on winter snow slowly melting in the mountains and providing a steady supply of water during the dry summer months. But the amount of water in snowpack is on the decline here and across much of the world as global temperatures rise.
Several states are already seeing how that can play out. Federal scientists in Utah warned in early May that more water from the snowpack is sinking into the dry ground where it fell this year, rather than running off to supply streams and rivers. With the state’s snowpack at 52% of normal, streamflows are expected to be well below normal through the summer, with some places at less than 20%.
It’s important to understand that drought today isn’t only about nature .