Skip to content
Scuba divers begin 6-month effort to rid Lake Tahoe of trash

The conversation

Dangerous fire season looms as drought-stricken western US heads for water crisis

Almost all drought indicators are flashing red in the western United States after a dry winter and a warm start to spring. The snowpack is less than half normal over much of the region. Reservoirs are shrinking, river levels are falling and soils are drying out. It’s only May, and states are already considering water use restrictions to extend supply. The governor of California has declared a drought emergency in 41 of 58 counties. In Utah, irrigation water providers increase fines for overuse. Some Idaho ranchers are talking about selling their cattle because the rivers and reservoirs they depend on are dangerously low and the demand for irrigation for farms is just beginning. Scientists are also closely monitoring the impact 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 what should already be another dangerous fire season. On May 13, 2021, US Home Secretary Deb Haaland and Agriculture Secretary Tom Vilsack told reporters that federal firefighters had warned them to prepare for an extremely active year of fire. “We used to call it fire season, but wildfires now spread throughout the year, burning hotter and becoming more catastrophic in drier conditions due to climate change,” said Vilsack. As climatologists, we follow these changes. Right now, about 84% of the western United States is under some level of drought, and there is no sign of relief. The US Drought Monitor from mid-May shows that nearly half of the West is in severe or extreme drought. National Drought Mitigation Center / USDA / NOAA The Many Faces of Drought Several types of drought are converging in the West this year, and all are at or near record highs. When too little rain and snow falls, it is called a meteorological drought. In April, precipitation in large parts of the west was below 10% of normal and the lack of rain continued until May. Rivers, lakes, streams and groundwater can enter what is called a hydrological drought when their water level drops. Many states are now warning of low flow after a winter with below normal snowfall and warm spring temperatures in early 2021 accelerating the melt. The U.S. Bureau of Salvage said Lake Mead, a giant Colorado River reservoir that provides water to millions of people, is set to drop to levels in June that could trigger the first federal declaration of water scarcity, with water use restrictions across the region. Another problem known as agricultural drought is the decrease in soil moisture. Average soil moisture levels in the western United States in April were at or near their lowest levels in more than 120 years of observations. Four signs of drought. Climate Toolbox These factors can all drive ecosystems beyond their thresholds – in a condition called ecological drought – and the results can be dangerous and costly. Northern California fish hatcheries have started trucking their salmon into the Pacific Ocean, rather than releasing it into rivers, as the river’s water is expected to be at historically low levels and too warm for young salmon tolerate it. Snow drought One of the West’s biggest water problems this year is the weak snowpack. The western United States relies heavily on winter snow that slowly melts in the mountains and provides a constant supply of water during the dry summer months. But the amount of water in the snowpack is declining here and in much of the world as global temperatures rise. Several states are already seeing how this can unfold. 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 flowing to feed streams and rivers. With the state’s snowpack at 52% of normal, flows are expected to be well below normal throughout the summer, with some places below 20%. Snowpack is generally measured by the amount of water it contains, called the water equivalent of snow. National Resource Conservation Service Human Drought It is important to understand that today’s drought is not just about nature. More and more people are moving to the American West, increasing the demand for water and irrigated farmland. And global warming – driven by human activities like the burning of fossil fuels – is now fueling more widespread and intense droughts in the region. These two factors act as additional straws to draw water from an already scarce resource. As the demand for water has increased, the West is pumping more groundwater for irrigation and other needs. Centuries-old groundwater supplies in aquifers can provide resistance to droughts if used sustainably. But groundwater supplies are slowly recharging, and the West is seeing a decline in these resources, mainly because the use of water for agriculture exceeds their recharge. Water levels in some wells have dropped at a rate of 6.5 feet (2 meters) per year. The result is that these regions are less able to handle droughts when nature brings hot and dry conditions. California hatcheries have started trucking their salmon into the Pacific Ocean because the rivers they are typically released into are too low and too hot. AP Photo / Rich Podroncelli Rising global temperatures also play several roles in the drought. They influence whether precipitation falls as snow or rain, how quickly snow melts and, most importantly, how quickly land, trees and vegetation dry out. Extreme heat and droughts can intensify. Solar radiation causes water to evaporate, drying out the soil and the air. With less humidity, the soil and the air heat up, which dries out the soil even more. The result is extremely dry trees and grasses that can burn quickly when fires start, as well as thirstier soils that require more irrigation. Alarmingly, the trigger for the dry and warm cycle has changed. In the 1930s, a lack of precipitation triggered this cycle, but excess heat initiated the process in recent decades. As global warming increases temperatures, soil moisture evaporates earlier and at higher rates, drying out the soils and triggering the warming and drying cycle. Upcoming Fire Warnings Hot, dry conditions in the West last year fueled a record-breaking wildfire season that burned more than 15,900 square miles (41,270 square kilometers), including the largest fires never recorded in Colorado and California. As the drought persists, the risk of large and disastrous fires increases. The seasonal outlook for hotter and drier than normal conditions for the summer and the outlook for the fire season by federal agencies suggests another difficult and long fire year is ahead. [Get the best of The Conversation, every weekend. Sign up for our weekly newsletter.] This article has been updated with a statement from Secretaries Deb Haaland and Tom Vilsack. This article is republished from The Conversation, a nonprofit news site dedicated to sharing ideas from academic experts. It was written by: Mojtaba Sadegh, Boise State University; Amir AghaKouchak, University of California, Irvine, and John Abatzoglou, University of California, Merced. Read more: Water wells risked to dry up in US and world Two-thirds of Earth’s land is on the verge of losing water as the climate warms – it is a problem for people, crops and forests Mojtaba Sadegh receives funding from the National Science Foundation. Amir AghaKouchak receives funding from the National Science Foundation, the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration; John Abatzoglou receives funding from the National Oceanic and Atmospheric Administration and the National Science Foundation.

Source link