Annual forest area burned (AFAB) in the western United States (US) has increased as a positive exponential function of rising aridity in recent decades. This non-linear response has important implications for AFAB in a changing climate, yet the cause of the exponential AFAB-aridity relationship has not been given rigorous attention. We investigated the exponential AFAB-aridity relationship in western US forests using a new 1984-2019 database of fire events and 2001-2020 satellite-based records of daily fire growth. While forest-fire frequency and duration grow linearly with aridity, the exponential AFAB-aridity relationship results from the exponential growth rates of individual fires. Larger fires generally have more potential for growth due to more extensive firelines. Thus, forces that promote fire growth, such as aridification, have more potent effects on larger fires. As aridity increases linearly, the potential for growth of large fires accelerates, leading to exponential increases in AFAB.

Our fire database consists of 18,368 western US fire events from 1984 through 2019. A text file (west_US_fires_1984_2019.txt) provides a list of each fire event, including the fire’s name, discovery date, point location, total area burned, and forested area burned (see the corresponding readme.txt file for column labels). We also include NetCDF files of the 1-km map of forest fractional coverage (forest_type_frac.nc) and the 1-km maps of monthly burned area over 1984–2019 (burnarea_1984_2019.nc). More information on methodology can be found in the Supporting Information in the manuscript.

When using this database, please cite our manuscript:

Juang, C. S., Williams, A. P., Abatzoglou, J. T., Balch, J. K., Hurteau, M. D., & Moritz, M. A. (2022). Rapid growth of large forest fires drives the exponential response of annual forest-fire area to aridity in the western United States. Geophysical Research Letters, 49, e2021GL097131. https://doi.org/10.1029/2021GL097131.