Anchor Point National Wildfire Hazard/Risk Rating Model March 1, 2010

Transcription

1 Anchor Point National Wildfire Hazard/Risk Rating Model March 1, 2010

2 Summary The Anchor Point Group, LLC (APG) National Hazard And Risk Model (NO-HARM) is being created as a response to the growing need for accurate information on the threat of wildfire to structures in the United States. The potential for damage to structures as a result of wildfire is a growing problem as wildland fuels accumulate and greater numbers of people choose to build structures in areas subject to wildfire. The APG NO-HARM is a response to the need for the insurance industry to better assess hazard and risk due to wildfire. Model Components FireSheds Fire behavior modeling Historic wildfire disturbance context Proximity to fire stations Parcel and road density Integration of multiple scales Elevation and aspect adjustment Urban wildfire threat designation

3 FireSheds The NO-HARM incorporates a technique that breaks the landscape up into logical units based on the local topography (hills and valleys). Unlike many mapping models, NO-HARM divides up the landscape based on the topography of an area. This is optimal because it groups areas together that are most likely to be similar in terms of climate, vegetation, slope, and aspect. Using this technique, a structure is more likely to fall into a model rating that properly reflects the wildfire context relevant to that structure. This technique also reduces the impact of inconsistencies (high or low) in the underlying data.

4 Fire Behavior Modeling Fire behavior modeling is one of the best predictive tools available to determine the threat from wildfire. It incorporates elements of the physical landscape (slope, aspect, elevation) along with the specific fuel types and climatological information in the form of fuel moisture information. The APG fire behavior modeling system takes state-of-the-art model inputs and, informed by decades of wildfire suppression and fire modeling experience, creates predictions of flame lengths and rates of spread. These pieces of information are vital in assessing the hazard/risk of structures due to wildfire. Flame lengths indicate the severity of fire effects and available suppression techniques. Rates of spread are indicative of the speed with which the fire will move and, therefore, the amount of time before a structure will be impacted, in the absence of fire fighter intervention.

5 Historic Wildfire Disturbance Context The best way to predict the future is to look at the past. Historic frequency and severity of wildfire can be informative as to the potential for wildfire activity in the future. Historic information about how often, how large and how severe wildfires have been in the past can help to predict the risk to structures in current conditions. The historic wildfire disturbance context model takes modeled conditions from the time before European settlement and compares them with the conditions that exist today. If there is significant departure between historical and current conditions, the implication is that the threat of wildfire to structures is potentially greater. This could be due to a build-up of fuel or to the threat of fire effects that are outside the range of ecological conditions that a landscape is adapted to experience.

6 Proximity to Nearest Fire Station When a fire starts, greater distances between a structure and the nearest fire station may reduce the survivability of a structure in the event of a wildland fire. If a fire station is farther away from a structure, it can mean that it takes longer for a response to a wildfire event. Small amounts of time can determine whether a structure will be defended or not.

7 Parcel and Road Density The density of parcels and roads can be a proxy for likelihood of ignition. Greater density of parcels and roads probably points to a higher number of people frequenting those locations. Larger numbers of people can mean higher likelihood of some types of ignitions. Humancaused ignitions, accidental or intentional, are one of the most frequent generators of wildland fires.

8 Integration of Multiple Scales A structure s threat from wildland fire is not only based on fuel that is immediately adjacent to it. Area surrounding a structure can also have an impact on the hazard/risk of wildfire to a structure. Wildfires can have an impact on structures beyond the immediate environment of a house, though the area closer to the structure probably better reflects wildfire threat. An example is that direct flame impingement will only occur very close to a house, but ember cast can impact a structure from a distance beyond the vegetation immediately surrounding it. By addressing wildfire threat at multiple scales, different types of impacts can be considered simultaneously.

9 Elevation and aspect adjustment Due to the shorter fire season at higher elevations (and northern aspects), the probability element of wildland fire impacts must be adjusted. There are simply not as many days per year that higher elevations (and northern aspects) are susceptible to wildfire. Higher elevation areas have snow earlier and later each fire season than do lower elevation areas. The window of opportunity, in terms of the length of the fire season, is just much smaller at higher elevation. For similar reasons, areas (in the northern hemisphere) that are north-facing have a similar (though less dramatic) situation. All other things being equal, areas at higher elevation and with north-facing aspects, face a reduced hazard due to wildfire. The NO-HARM incorporates an adjustment factor that equalizes the threat level between high- and low-elevation areas.

10 Urban Wildfire Threat Designation Urban areas do not reflect wildfire hazard/risk in the same way that pure tracts of wildland fuel do. This difference is reflected in the Urban Wildfire Threat Designation model. It assigns threat to urban areas based on the proximity of FireShedsTM with extreme potential fire behavior. Due to limitations of model inputs, it is not possible to assign hazard/risk to areas that have a large urban core, nor would it be appropriate. It is also inappropriate to assume that structures in urban areas cannot burn. A separate technique was developed to address this situation. The primary threat to structures in urban areas is ember cast (or spotting). To address the threat of spotting, a distance buffers into urban areas are combined with identification of extreme fire behavior in adjacent wildland fuel areas.