Authors
Maya Robinson (CIRES,NOAA/PSL), Melissa Breeden (CIRES,NOAA/PSL)

Abstract

The Western US has experienced elevated wildland fire conditions in recent years, largely due to enhanced drought conditions related to a combination of forced and internal variability. This has led to increasing negative impacts on the public and the environment. Vapor pressure deficit (VPD), the difference between actual and saturation vapor pressure, is significantly related to annual mean area burned, and has been increasing in tandem with the elevated wildland fire in recent years. We seek to understand potential sources of predictability of seasonal fire conditions in the Western US, with the goal of creating a skillful forecast of these conditions that can be used by various end-users to better prepare for intense fire seasons and reduce their impact. For this analysis, we are using the burned areas boundaries dataset from the Monitoring Trends in Burn Severity (MTBS) program as our estimate of area burned by wildland fires across the US from 1984-2021. We also use 2 meter VPD from the European Centre for Medium-Range Weather Forecasts fifth generation atmospheric reanalysis, nClimGrid precipitation and 2 meter temperature from the National Centers for Environmental Information (NCEI), and Daily Optimum Interpolation Sea Surface Temperature (SST) from NCEI. We find that enhanced area burned in June-August is often associated with increased temperatures and VPD, and decreased precipitation starting approximately in the immediately prior spring (March-May). Additionally, increased June-August area burned is associated with cooler SSTs in the eastern Pacific in the seasons leading up to June-August. A linear stochastic model produces high seasonal forecast skill of VPD during summer that is dominated by a long-term warming trend, with additional skill contributions from SST’s and soil moisture for lead times up to six months. Upcoming work will examine the 2020 fire year in more detail, a particularly intense wildfire year that saw fires such as the Cameron Peak and East Troublesome fires.