Towards a processed-based understanding of climate-fire relationships of the western United States

Increased wildfire activity coincident with widespread warming across the Western US in recent decades has suggested a link between temperature and fire, particularly in forested areas of the western US due to the combined effects of temperature on mountain snowpack and moisture deficits on the length of fire season. It is critical to elucidate the biophysical mechanisms through which warming influences wildfire potential in the face of projected changes over the next century. This study hypothesizes that information from National Fire Danger Rating System and the Variable Infiltration Capacity model comprise a more direct and processed-based link between climate on wildfire potential than widely used temperature, precipitation and drought data. Macroscale climate-fire relationships examined across Geographic Area Coordination Centers (GACCs) in the western US using area burned derived from the Monitoring Trends in Burn Severity dataset from 1984-2008 generally support prior analyses in fuel and flammability limited systems in the West. Unlike previous studies, spring temperature and timing of mountain snowmelt were not correlated to fire activity outside of the Rocky Mountain and Southwest GACC. Instead, in-season temperature, precipitation and humidity exhibited strong links to fire activity commonly across GACCs. Finally, fuel and soil moisture were generally found to be more strongly correlated to area burned than standard climate data. Results highlight the indirect influence of temperature on fire potential through its effect on in-season relative humidity and fuel moisture, suggesting that temperature should be contextualized through metrics that biophysically link climate to wildfire to better predict fire activity.