Effects of climate change on snowpack and fire potential in the western USA

We evaluate the implications of ten twenty-first century climate scenarios for snow, soil moisture, and fuel moisture across the conterminous western USA using the Variable Infiltration Capacity (VIC) hydrology model. A decline in mountain snowpack, an advance in the timing of spring melt, and a reduction in snow season are projected for five mountain ranges in the region. For the southernmost range (the White Mountains), spring snow at most elevations will disappear by the end of the twenty-first century. We investigate soil and fuel moisture changes for the five mountain ranges and for six lowland regions. The accelerated depletion of mountain snowpack due to warming leads to reduced summer soil moisture across mountain environments. Similarly, warmer and drier summers lead to decreases of up to 25% in dead fuel moisture across all mountain ranges. Collective declines in spring mountain snowpack, summer soil moisture, and fuel moisture across western mountain ranges will increase fire potential in flammability-limited forested systems where fuels are not limiting. Projected changes in fire potential in predominately fuel-limited systems at lower elevations are more uncertain given the confounding signals between projected changes in soil moisture and fuel moisture.