One other harmful hearth season looms within the western US and the drought-stricken area faces a water disaster – Watts Up With That?
Mojtaba Sadegh, Boise State University; Amir AghaKouchak, University of California, Irvine, and John Abatzoglou, University of California, Merced
Almost every indicator of drought in the western United States flashes red after a dry winter and warm early spring. The snowpack is less than half as normal in large parts of the region. Reservoirs are being dismantled, river levels are sinking and the soil is drying up.
It’s only May and states are already considering restrictions on water use to extend supplies. The governor of California declared a drought emergency in 41 counties out of 58. In Utah, irrigation water providers are increasing fines for overuse. Some Idaho ranchers talk about selling cattle because the rivers and reservoirs they rely on are dangerously low and the demand for irrigation for farms is just beginning.
Scientists are also closely monitoring the effects of rapid warming and drying on trees, fearing that water stress could lead to widespread tree death. Dead and drying vegetation means more fuel for another dangerous fire season.
U.S. Secretary of the Interior Deb Haaland and Agriculture Secretary Tom Vilsack told reporters on May 13, 2021 that federal firefighters had warned them to prepare for an extremely active year of fire. “We used to call it fire season, but now forest fires extend year-round, burn hotter, and become more catastrophic in drier conditions due to climate change,” Vilsack said.
As climate researchers, we are tracking these changes. Some 84% of the western US is currently experiencing some drought and there are no signs of relief.
The US Drought Monitor for mid-May shows almost half of the West in severe or extreme drought. National Drought Reduction Center / USDA / NOAA
The many faces of the drought
This year, different types of drought are converging in the west, and all of them are at or near record levels.
If too little rain and snow falls, we speak of a meteorological drought. In April, precipitation was below 10% of normal in much of the west, and the lack of rain persisted into May.
Rivers, lakes, streams and groundwater can get into what is known as hydrological drought when the water level drops. Many states are now warning of low electricity flow after a winter of less-than-normal snowfall and warm spring temperatures that are accelerating the melting. The US Bureau of Reclamation announced that it would cut water on a canal serving farms in the Klamath Project on the Oregon-California border due to poor water supplies. It also warned that Lake Mead, a huge reservoir on the Colorado River that supplies water to millions of people, will drop in June to levels that could trigger the first federal water shortage declaration, with water use restrictions across the region.
The dwindling soil moisture creates another problem known as agricultural drought. Average soil moisture in the western United States in April was at or near the lowest level in over 120 years of observation.
Four signs of drought. Climate toolbox
These factors can push all ecosystems beyond their thresholds – into a state called ecological drought – and the results can be dangerous and costly. Fish hatcheries in Northern California have started moving their salmon to the Pacific Ocean instead of releasing them into rivers, as river water is expected to be historically low and too warm for young salmon to tolerate.
Snow drought
One of the biggest water problems in the west this year is the low snow cover.
The west of the USA is crucially dependent on the winter snow slowly melting in the mountains and ensuring a steady water supply in the dry summer months. But the amount of water in the snowpack is decreasing here and in large parts of the world with increasing global temperatures.
Several states are already seeing the effects of this. Federal scientists in Utah warned in early May that more water is sinking from the snowpack into the dry ground, where it fell this year, rather than draining to supply streams and rivers. With the state’s snowpack at 52% of normal, electricity flows are expected to be well below normal in summer, with some locations being less than 20%.
Snow cover is usually measured by the amount of water known as the snow water equivalent. National Resource Conservation Service
Anthropogenic drought
It’s important to understand that drought today isn’t just about nature.
More and more people are moving to the western United States, which increases the demand for water and irrigated farmland. And global warming – fueled by human activities like fossil fuel burning – is now causing widespread and more intense drought in the region. These two factors act as extra straws drawing water from an already scarce resource.
As the demand for water has increased, the West pumps out more groundwater for irrigation and other needs. Centuries-old groundwater reserves in aquifers can offer resilience to droughts if used sustainably. However, groundwater reserves are slowly being recharged and these resources have been declining in the west, largely as water use for agriculture exceeds replenishment. The water level in some wells has decreased at a rate of 2 meters per year.
The result is that these regions are less able to cope with droughts when nature brings hot, dry conditions with it.
Rising global temperatures also play several roles in drought. They influence whether precipitation falls as snow or rain, how quickly snow melts and, above all, how quickly land, trees and vegetation dry out.
Extreme heat and drought can be mutually reinforcing. Sunlight evaporates water and dries out the ground and air. With less moisture, the soil and air heat up, which dries the soil even more. The result is extremely dry trees and grasses that can burn quickly if a fire breaks out, as well as thirstier soils that require more watering.
It is alarming that the trigger for the drying and heating cycle has changed. In the 1930s, the lack of precipitation started this cycle, but excess heat has started the process for the past few decades. As global warming increases temperatures, soil moisture evaporates sooner and at a greater rate, drying out the soils and triggering the warming and drying cycle.
Fire warnings ahead
The hot, dry conditions in the west last year resulted in a record-breaking wildfire season that included the largest fires in Colorado and California.
If the drought continues, the likelihood of major, catastrophic fires increases. Federal agencies’ seasonal outlook for warmer and drier than normal conditions for the summer and fire seasons suggests another tough, long fire year is ahead.
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This article has been updated with a statement from Secretaries Deb Haaland and Tom Vilsack.
Mojtaba Sadegh, Assistant Professor of Civil Engineering, Boise State University; Amir AghaKouchak, Associate Professor of Civil and Environmental Engineering at the University of California at Irvine; and John Abatzoglou, Associate Professor of Engineering at the University of California at Merced
This article is republished by The Conversation under a Creative Commons license. Read the original article.
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