"The threat is here": A severe US heatwave poses a problem for wildfire season and water supply.

A severe heatwave that shattered records in the western United States is rapidly melting the already scarce snowpack and increasing the risk of wildfires in the coming seasons. March has already been exceptionally hot, and the early onset of summer-like weather may persist throughout the region. Forecasts offer little relief, suggesting that more heat records could be broken this spring. Extreme heat is particularly dangerous, especially early in the year when bodies and systems are not prepared for it and when it persists for extended periods. This heatwave also poses significant threats to the water supply. Following one of the warmest winters in the West, the snow that feeds streams, reservoirs, and soil moisture is already critically low in key watersheds. "Anomalous warmth and a historic snow drought will continue to cause ecological and wildfire-related impacts this spring, and potentially broader water challenges by late summer and beyond," said climate scientist Daniel Swain. His primary concern is in the interior West, particularly the Colorado River basin, which could face "water supply and hydroelectric shortfalls, an early and intense fire season, and ecosystem degradation." This unprecedented heat event pushed temperatures 20 to 30 degrees Fahrenheit above average across the region, with some areas experiencing spikes of up to 40 degrees Fahrenheit above normal. Heat records for March have already been broken in at least 14 states. A new national temperature record for the month was shattered last Thursday when a location in Arizona reached 110°F (43.3°C). This record was quickly broken on Friday when parts of California and Arizona reached 112°F (44.4°C), just one degree shy of April's heat record. More than 400 daily records were broken last Thursday when the heatwave peaked, caused by a large and persistent high-pressure system over the western United States. However, "this is not going to be a heat event that suddenly disappears," Swain said. "We are still going to be experiencing record warmth and dryness next week – at least for the next seven to ten days." Forecasters predict that hundreds more high-temperature records could be broken this week as the extreme heat moves eastward. "High temperatures are forecast to reach 20-25 degrees above average," forecasters with the National Weather Service reported on Monday, noting the potential to break numerous records across the southwestern, inter-mountain western, and central United States. The heatwave has further depleted the already scarce snowpack, which is crucial for sustaining water resources during the drier months. This scorching spring follows a record-warm winter for nearly every major river basin in the West, according to the federal drought monitor, pushing the region into a snow drought even before temperatures spiked. By March 8th, measurements of water frozen within the snow were below the median at 91% of western stations. By mid-March, more than half of the continental United States had already been classified in moderate to exceptional drought conditions. "Drought conditions worsened or developed across much of the Great Plains, Lower Mississippi Valley, and southeastern United States due to warmer and drier-than-normal conditions this winter," said Jon Gottschalck, chief of the Operational Prediction Branch at NOAA's Climate Prediction Center, in a spring outlook published on Friday. The agency anticipates that drought will persist and expand across the West due to the unrelenting heat. The heat also evaporates more moisture from the landscape, amplifying wildfire risks and extending the seasons when ignitions can quickly escalate into large fires. The hot, dry conditions are fueling an explosive start to the high-risk wildfire season, and vegetation is becoming increasingly primed to burn. "With fuel moistures trending near record lows for this time of year, similar conditions could support fast-moving fires and new large fire activity when winds align," officials with the US National Interagency Fire Center wrote on Friday. More than 1.4 million acres have already burned this year, more than double the 10-year average for the same period, largely due to major fires that erupted in Nebraska this month. Two fires in the state spread across more than 800,000 acres, consuming parched grasses. The Morrill fire in west-central Nebraska alone grew to over 640,000 acres, making it the largest in the state's history. The blaze was 65% contained as of Monday. An analysis by World Weather Attribution, a collaboration of climate scientists, found that the extreme heat impacting the region would be virtually impossible without the climate crisis and signals the dangers of what's to come. "These findings leave no room for doubt. Climate change is pushing weather into extremes that would have been unthinkable in a pre-industrial world," said Friederike Otto, a climate science professor at Imperial College London. "In the US West, the seasons that people and nature have become accustomed to for centuries are disappearing, putting many, including outdoor workers and those without air conditioning, in danger." She added, "The threat isn't distant – it is here, it is worsening, and our policies must catch up with reality."