Boulder County, Colorado

Boulder County, CO is located 40 miles northwest of Denver, Colorado on the eastern side of the Rocky Mountains. Covering approximately 750 square miles, the county lands range from the semi-arid eastern grasslands and plains through the montane forests of the foothills to the alpine tundras along the Continental Divide. Steep rugged canyons, strong Chinook and Bora winds, and semi-arid conditions describe the physical conditions of the county's mountainous area. Local city and county open space lands along with federal lands comprise over half of the western 450 square miles of the county. These public lands intermix with private landholdings in the form of old subdivisions and town sites, mining claims, and three incorporated towns. Eighteen local fire protection districts serve the mountainous western half of the county.

The Problem

The possibility of a wildfire is an ever-present danger in the Colorado Front Range. Eighty years of fire suppression preceded by earlier European settler grazing have left the forests with vegetation densities 10 to 100 times their historic levels. This results in fires that are more intense and devastating than the previous historical norm. Combined with increased residential development and high recreation demands in the mountains, the potential for catastrophic wildfire has reached crisis levels.

The Urban Wildland Interface

Throughout the west, an increasing number of people are moving away from urban centers into more rural or wildland fringes. The intermixing of structures with wildland vegetation creates a significant fire management problem. In one case, wildland fuels are partially dependent upon or adapted to fire as part of their environment. In the other case, residential and other structures are not compatible with a fire environment. This mixture of two different types of fuel with different tolerances for the presence of fire is the crux of the wildfire management problem in the urban wildland interface. The urban wildland interface (UWI) is a term used to refer to a geographic area in which flammable wildland fuels are in close proximity to urban/suburban structures.

Within the past few years, Boulder County has experienced wildfires, both large and small. The situation in Boulder County reached a crisis point in 1989, when the Black Tiger Fire consumed 44 homes and blackened over 2,000 acres of forested land in the western part of the county just five miles from the city of Boulder.

The Response

In 1990, under a mandate from the Federal Emergency Management Agency (FEMA), agencies and individuals involved in the Black Tiger Fire produced a report that formed the wildfire portion of the Colorado Natural Hazards Mitigation Plan. By directive of the Board of County Commissioners, that investigative group evolved into the Boulder County Wildfire Mitigation Group (BCWMG), chaired by staff in the County Land Use Department and consisting of members from County Departments, County Fire Protection Districts, the Colorado State Forest Service, the City of Boulder, federal land management agencies, and private citizens. The group's mission was to determine and coordinate actions that could help minimize loss of life and property from future wildfires.

By 1992, a technical team from the BCWMG began designing and developing what is now referred to as the Wildfire Hazard Identification and Mitigation System (WHIMS). WHIMS strives to identify wildfire hazards, educate homeowners, assist land managers, and assess the risks involved due to wildfires. In addition, it aims to assist in pre-attack planning, emergency response planning, land use planning, and disaster assessment. With involvement of public and private agencies and individuals from the community, WHIMS combines hazard assessment, forest management, land use planning, building safety, wildfire behavior, and fire suppression expertise with geographic data management and analysis technologies.

The Approach

Lot boundaries and ownership information are extracted from County Assessor's parcel ownership database. Topographic information is extracted from USGS digital elevation model data (DEM). Fuel type data were specifically mapped for the county, and parcel-specific hazard data are collected on-site using a specially designed questionnaire (WHIMS questionnaire). The questionnaire, developed with wildfire hazard experts, is filled out on-site by fire fighters involving personal contact with homeowners whenever possible.

Two levels of spatial focus are a part of the project. The more broad level of analysis occurs county-wide and the site-specific analysis is focused on individual parcels. The parcel-specific analysis fully nests within the county-wide broad analysis and are directly linked through the spatial database maintained within the GIS.

Wildfire Hazard Assessment

Assessed using a hazard-rating model - WHINFOE
Based upon the BEHAVE wildfire behavior model & the expert opinion of wildfire behavior specialists
Overall hazard rating and individual factor ratings are produced

Basic Structure of the Model

A hierarchical model with 3 factor categories that group 7 primary factors

Base Hazard Category is the hazard that is due just to the existence and characteristics of the first three factors, the ‘burnable stuff’. This category is made up of Topographic and Fuels (County-wide & Parcel Specific), Building Construction and Design (Parcel Specific), and Landscaping – Site Fuel Density & Arrangement within 150 feet (Parcel Specific).

Passive Protection Category measures the existence of Defensible Space, which if present causes a decrease in fire intensities so that a structure can survive the passage of the flame front, or so that fire fighters can more easily protect the structure. (Parcel Specific)

Active Protection Category is made up of Accessibility, Fire Protection Response Time, and Water Availability. (Parcel & Subdivision Specific)

The Passive and Active Protection Categories contribute to reducing the Base Hazard based upon an evaluation of a protective zone around a structure (Defensible Space) and of the suppression resources available to fight a fire.

Next Steps

House Pad Locations

Acquire actual house pads locations within a parcel so that structure focused proximity analysis can be performed with in the GIS as opposed to parcel-aggregated evaluations.
Such data would improve the analysis of topographic data relative to structure location on large parcels
Such data would also solve the multiple structures per parcel problem in the most efficient way

County-wide Dangerous Topography Layer

A dangerous topography evaluation is part of the parcel-based evaluations, and is evaluated directly on site for each structure. This short fall in the countywide hazard classification is due to the fact that a dangerous topography data layer has not been developed as yet for the entire county. Plans to acquire this information are currently being developed.

Countywide Risk Evaluation

The county is currently undertaking a countywide risk ‘first look’ evaluation where risk is the probability of an event occurring. That information will be combined with the hazard/values at risk classifications for a follow-on county-wide integrated hazard-risk evaluation to be used to guide planners in the site plan review process for new or remodel building permits.

Acknowledgements

The authors wish to acknowledge that parts of this text are extracted from the WHIMS Manual with contributions from Nan Johnson, City of Flagstaff Planning Department and Chris White, Boulder County Fire Management.