The Western United States MTBS-Interagency database of large wildfires, 1984–2024 (WUMI2024a)

Abstract. Wildfire regimes of the western United States (US) have changed dramatically since the 1980s but our understanding of the causes and effects of these changes is limited by a lack of a quality-controlled, publicly available wildfire database that (1) spans from the 1980s to present, (2) represents wildfires across a wide range of sizes, and (3) includes mapped fire perimeters and the areas burned within. Here we present an updated and improved Western US MTBS-Interagency database (WUMI2024a) of wildfire occurrences, perimeters, and burned-area maps, covering the period 1984–2024 and the geographic domain of the 11 westernmost states in the contiguous US. The database represents 22 234 wildfires ≥ 1 km2 in size, which we compile by merging seven publicly available government databases. For over 47 % of wildfires in our database (more than 10 300 wildfires), the maps of fire perimeters and area burned are based on 30 m satellite data provided by the US government's Monitoring Trends in Burn Severity (MTBS) project, allowing our mapping and assessments of total area burned to account for heterogeneity within fire boundaries. For another 24 % of fires, our database includes perimeter observations provided by non-MTBS sources, meaning that only 29 % of fire occurrences are without perimeter observations. For these fires, which are generally small and account for <5 % of total burned area in the database, we tentatively assume perimeters are circular centred on the ignition location, but with shapes adjusted to not include areas dominated by open water or barren ground. The fire perimeters and burned area maps in our database are intended to improve assessments of temporal variations and trends in wildfire frequency and area burned, assessments of the landcover types that burn, and simulations of how historical fires have affected ecosystems, smoke emissions, and hydrology. The WUMI2024a can be quickly updated as new and improved data become available. The WUMI2024a dataset and the code used to produce the dataset are available at https://doi.org/10.5061/dryad.63xsj3vd4 (Williams et al., 2025a).