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Wildfires in the Western U.S. are becoming more frequent and the wildfire season is lengthening, driven by regional temperature increases that are double the global average and earlier spring snowmelt.

Climate change is increasing the number of winter days with minimum temperatures above freezing across the Northern Hemisphere, leading to a reduction in snow cover and freshwater supplies. In the contiguous U.S., annual snowfall has decreased at 64% of 2,041 stations since 1970, and snow-derived freshwater in the western U.S. has fallen by 15-30% since 1955, with a further 25% decline projected by 2050.

Human-caused warming increases atmospheric thirst, leading to higher evaporation and transpiration, which worsens droughts globally and specifically in the western U.S. In the southwestern U.S., the 2000-2021 megadrought was the most severe in 1,200 years, with over 40% of its severity attributed to climate change. The western U.S. faces increasing risks of hydrological drought from declining snowpack and compound events involving heat, drought, and wildfires, which caused over $38 billion in damages during 2020-2021.

Climate change is identified as a significant driver of altered fire activity in the Western United States, where rising temperatures and earlier snowmelt are linked to more frequent and longer-lasting large wildfires.