US wildfire, 2021- Forensic analysis

Step 1 - Understanding the disaster DNA

What Happened?

In December 2021, Boulder County experienced the most destructive wildfire in Colorado's history. The fire began in a grassy area in the suburban town of Marshall and spread rapidly due to strong winds, which reached up to 160 kilometres per hour (45 meters per second). An unusually wet spring had led to abundant grass growth, which, combined with an exceptionally warm and dry summer and fall, followed by a lack of snow, created ideal conditions for the fire to spread quickly.

Despite early and accurate warnings, the fire spread rapidly and unexpectedly. It caused an estimated $500 million in damages. Severe wildfires like this one also have impacts which stretch into the long-term, including erosion, mudslides, road closures, degraded water quality and lives that need to be rebuilt.

Exposure: Where was damage concentrated?

More than 1,000 homes were destroyed in the towns of Superior and Louisville, as well as in unincorporated areas of Boulder County. The level of destruction in these suburban communities was unprecedented. Within less than 24 hours, the fire had burned over 2,500 hectares (about 6,200 acres) of land.

The fire released toxic polycyclic aromatic hydrocarbons into the air, posing long-term health risks. Elevated levels of these carcinogens were found in the dust within homes, raising concerns about respiratory and other health issues.

Natural hazards, including high wind and drought, played a vital role. These hazards, combined with unusual weather, abundant vegetative growth, the area's natural topography, and characteristics of the built environment - such as dense suburban housing and interwoven green spaces - propelled the fire.

Vulnerability: Who was affected and why?

The severity and behaviour of the Marshall Fire were influenced by several factors. Many affected areas had design features that inadvertently increased wildfire vulnerabilities. Elements such as drainage ditches for flood control and greenbelts for recreation acted as wildfire "superhighways" due to unmanaged biomass and hazardous vegetation. These open spaces and extensive grasslands allowed the fire to penetrate deeper into built environments. While valuable for flood control and recreation, they exacerbated the fire's spread by channelling winds and increasing fire intensity. In addition, highly flammable materials, such as wooden roofs and dense vegetation close to homes, contributed to the extensive damage.

The use of flammable building materials and the lack of fire-resistant building codes for existing structures further increased vulnerability and the extent of the damage. Key factors affecting a home's wildfire risk included construction materials, proximity to fire hydrants or stations, elevation, emergency vehicle access, nearby vegetation, and weather patterns. Several manufactured home communities in Boulder County were heavily damaged or destroyed by high winds during the Marshall Fire.

Power interruptions restricted the response by limiting water availability from hydrants, ponds, lakes, and stormwater facilities. Low water pressure in community hydrants also hampered firefighting efforts. High winds made air suppression unusable, as firefighters reported that the winds either blew the water from hoses back at them or dispersed it into a fine mist.

Evacuation was complicated by several challenges, including compromised power, gas and water lines, congested roads, and sub-zero temperatures. Lower-income and vulnerable populations faced additional challenges. These groups, including older adults, persons with disabilities, and those without reliable transportation, often had limited access to emergency services and support networks.

Insufficient insurance coverage added to the pain. The fire's rapid spread caused many people to lose everything they owned. Residents discovered that their insurance did not cover the full cost of rebuilding, leading to financial strain and prolonged recovery. This vulnerability was particularly severe for those already struggling before the fire. The destruction of commercial properties and job losses also created economic hardships, especially for those without financial safety nets.

Resilience: what factors limited the impacts?

Nationally, building codes and regulations existed to mitigate fire risk, including requirements for fire-resistant construction materials and defensible space around buildings. However, enforcement and specificity varied across regions, as the Marshall Fire showed.

The Colorado State Forest Service's Wildfire Risk Map delineated wildfire risk, including burn probability maps and reference layers such as large fire perimeters, community wildfire protection plan boundaries, Firewise USA sites, and a social vulnerability index. Tools available included a wildfire risk reduction planner and a wildfire risk viewer.

At the time of the Marshall Fire, Colorado lacked a wildland-urban interface code covering the transition zone between unoccupied land and human development. Wildfire-specific standards were insufficient. The state's enhanced hazard mitigation plan (E-SHMP), updated and approved in 2023, now includes eight goals:

1. Minimize the loss of life and personal injuries from natural hazard events.
2. Reduce losses and damages to state, tribal, and local governments, as well as private assets.
3. Reduce federal, state, tribal, local, and private costs of disaster response and recovery.
4. Support mitigation initiatives and policies that promote disaster resiliency, nature-based solutions, cultural resources, historic preservation, and climate adaptation strategies.
5. Minimize interruptions to essential services and activities.
6. Incorporate equity considerations into all mitigation strategies.
7. Improve coordination of risk mitigation among public, private, and non-profit sectors.
8. Create awareness and demand for mitigation as standard practice.

Boulder County's 2020 Comprehensive Plan addressed wildfire threats, emphasizing codes, standards, public education, and land use management. It aimed to improve the wildfire resiliency of existing housing stock through voluntary incentives, such as low-interest loans for replacing wood roofs with Class A fire-rated roofs. However, this goal was yet incorporated into local ordinance and remained a voluntary approach.

Local municipalities had community wildfire protection plans, zoning regulations, and programs promoting fire-resistant landscaping and building materials. The effectiveness of these programs depended on local implementation and enforcement. Some plans incentivised homeowners to invest in resilience including through lower-cost insurance premiums.

Partnerships between local governments, fire departments, and community organizations, such as Restoring Our Community, played a crucial role in promoting wildfire resilience and supporting survivors in housing recovery.

Rather than relying on voluntary measures, the application of good governance measures - such as enforceable wildfire codes and state regulations - would decrease wildfire risk and increase the capacity of insurance companies to provide coverage, an example of making the "right investment". Likewise, through "meaningful inclusion" and "good governance", the Wildfire Partners Program has improved the insurability of homeowners. This, combined with grants for home improvements and additional grants through the May 2023 Colorado legislation are also examples of the "right investment". All these elements could help prevent future disasters.

Step 2: Future trends

People

• More than half of all Coloradans live in the wildland-urban interface (WUI), placing them at higher risk of wildfires.
• Continued urbanization of these areas increases the potential for future wildfires. Some states have witnessed more than 50 percent population growth in WUI areas between 1990 and 2020. This trend shows few signs of slowing in the future.
• Wildfire smoke in Colorado has been associated with increased hospitalizations for asthma, chronic obstructive pulmonary disease and some cardiovascular health outcomes.

Planet

• Since 2000, there have been 60 wildfires larger than 10,000 acres in Colorado, including six fires larger than 100,000 acres. All but one of these larger fires occurred after 2017. The annual area burned by wildfires in the forested areas of Colorado and adjacent areas of New Mexico and Wyoming increased by over 300 percent from the 1984-2000 period to the 2001-2017 period. The average elevation at which these wildfires occurred shifted upwards by over 1000 feet between 1984 and 2017, consistent with how warming is moving temperature regimes upslope. Wildfire risk in Colorado is expected to worsen significantly by the mid-21st century compared to the late 20th century, as additional warming further increases fuel dryness and enhances fire ignition and spread.
• On average 2.8 million acres of forest burn annually in the US.
• When unhealthy forests are in proximity to populated areas, with materials that act as high fuel loads, they can create destructive wildfires that spread to urban areas.

Prosperity

• Property loss due to wildfires increased by over 140 percent between 2013 and 2022, and this trend is not slowing.
• Homeowners face considerable financial burdens due to property damage, while communities incur high expenses related to firefighting and post-fire rehabilitation. Colorado is likely to be the next state to face extremely tight, or non-existent, homeowner insurance policies due to increasing wildfire threats. The average homeowner insurance premium in the state increased 51.7 percent between January 2019 and October 2022. Meanwhile, some new homeowners in the state are struggling to obtain insurance policies.
• CoreLogic, a firm that provides risk estimates to insurers, utilities and local governments, estimates that 332,716 homes in Colorado are at moderate, high or very high risk of damage from wildfires. Rebuilding those homes, if they were destroyed, would cost an estimated $140.9 billion. Colorado has the second highest wildfire exposure to its housing stock in the nation.

Step 3: Forensic learning

This section aims to encourage dialogue around the forensic analysis to foster improved decision making. The areas for consideration below are envisaged as an input to stimulate in-country discussion and action plan on future disaster prevention and enhanced disaster risk management.