Pyromes of the conterminous United States

This data publication contains a vector dataset (shapefile) depicting areas of relatively homogeneous contemporary fire regimes, based on an analysis of historical wildfire activity in the conterminous United States (CONUS) from 1992-2013 (Short 2015). The product was generated for use in landscape fire simulation for national wildfire hazard mapping and risk assessment, but should have other planning and research applications. The historical data were analyzed using a k-means clustering algorithm with 75 bins, five fire-regime statistics, and a 40-kilometer grid. Four of the statistics, fire season start date, end date, modality, and large-fire size were generated using a nearest-neighbor analysis (nearest 200 fires to each reported ignition) with the pixel values representing the median value for all fires ignited in each grid cell. The fifth statistic was total area burned by all fires originating in each cell. The resulting map clusters guided the subsequent process of assigning each of the 5901 individual polygons in the U.S. Environmental Protection Agency (EPA) Level IV Ecoregions dataset to pyromes. In addition to the k-means clusters, that work was visually informed by additional spatial datasets, including a maps of forested versus non-forested land, surface fire-behavior fuel models, and large fire footprints from 1984-2013. The latter was particularly helpful for identifying and delineating pyromes in which the large fires appeared to be largely long, narrow, wind-driven events. A total of 128 pyromes were delineated for CONUS, ranging in size from ~1.8 to 46 million (M) acres, with the largest containing substantial areas mapped as non-burnable by LANDFIRE, as in the corn-belt regions. The average size is 15M acres, which is comparable to the size of Fire Planning Units (FPUs) used for previous national wildfire hazard mapping efforts at 270-meter resolution (see Finney et al. 2011). Pyrome names were adapted from existing EPA Level III or IV Ecoregion names and should generally reflect the major contents of each.This map product, which depicts areas of relatively homogeneous contemporary wildfire regimes, was generated for use in landscape fire simulation for national wildfire hazard mapping and risk assessment.