MWRA Census County Divisions Summary

Tabular Summaries- Communities at Risk As part of [Montana DNRC’s Montana Wildfire Risk Assessment (MWRA)], wildfire risk to homes, commercial buildings, and other structures was assessed across the state. The purpose of this assessment is to identify the counties and communities whose structures are most threatened by wildfire—both on average and in total. The risk-to-structures methods used for this assessment are identical to the methods used for structures within the overall MWRA project. See earlier section 3.4.1 of the report (page 20) for details. This portion of the report addresses only the tabular summaries. The summary methods used in this section were customized to the MWRA results from similar methods previously developed for the [Pacific Northwest Risk Assessment (PNRA)] and for the national [Wildfire Risk to Communities (WRC)] project. The risk-to-structures results were summarized for four sets of summary polygons: 1. MT Counties 2. MT Census County Divisions 3. MT Communities (core plus zone combined) 4. MT Communities (core and zone separate) Each set of summary polygons captures nearly all structures in Montana, without overlap. In the MT Counties set, a summary polygon is an individual county (e.g. Ravalli County). In the MT Census County Divisions (CCD) set, a summary polygon is an individual CCD (e.g., the Sula CCD within Ravalli County). In the MT Communities (core plus zone combined) set, a summary polygon is the community core plus the zone surrounding the core (as defined below). In the MT Communities (core and zone separate) set, a summary polygon is either the community core or the zone surrounding the community core. There are 56 counties in Montana. Each Montana county is divided into at least two Census County Divisions (CCDs), with mean of 3.5 CCDs per county (194 CCDs in total) and a maximum of 11 (Flathead county). For this assessment, a community core was defined as a Populated Place Area (PPA) as identified by the U.S. Census Bureau. PPAs include incorporated cities and towns as well as Census Designated Places (CDPs). A CDP is an unincorporated concentration of population—a statistical counterpart to incorporated cities and towns. There are 364 PPAs across Montana. Of those, 127 (35 percent) are incorporated cities or towns, and 235 (65 percent) are CDPs. Two PPAs—Butte-Silver Bow and Anaconda-Deer Lodge—are unique in that they represent the balance of a county that is not otherwise incorporated; they are much larger in size than most PPAs. In the PPA dataset, the CDPs represent the location of highest concentration of population for a community; they do not include the less-densely populated areas surrounding the PPA. We refer to the U.S. Census PPA delineation as the community “core.” Approximately 66 percent of Montana’s total structure importance can be found within these PPA core areas (Figure A.1 of the Montana Wildfire Risk Assessment report). To include the populated area and structures surrounding the PPAs, Ager and others (2019) used a travel-time analysis to delineate the land areas closest by drive-time to each PPA core, up to a maximum of 45 minutes travel time. Approximately 33 percent of Montana’s total structure importance can be found within 45 minutes travel time of the cores. Only 1 percent of the total structure importance is not within 45-minutes travel time of any community core.