Executive Summary
The relationship between the pattern of residential development and the potential costs and losses from wildfire in the development area arises through interactions involving risk, hazard, institutional response and asset exposure. A general framework that links different development patterns to impacts on CDF workload and likely fire scenarios can assist fire managers in offering sound advice to developers and planning staffs to limit potential losses.
The framework suggests the following impacts of three archetypal development patterns on the four dimensions of the fire problem (risk, hazard, response and exposure):
TABLE 1. Fire Impacts Factors and Expected Costs and Losses by Development Pattern assuming development occurs in a high hazard area and fires occur under severe fire weather: cell entries indicate influence of the development pattern on the factor. Increases in risk, hazard, suppression difficulty, and exposure tend to increase expected costs and losses. The top mark indicates relative change in fire impacts factor for initial attack within development; the lower mark indicates relative change in factor given fire from outside development.
|
FACTOR |
2-acre |
Mixed-dispersed |
Mixed-clustered |
|
Risk |
+ N/A |
- N/A |
- N/A |
|
Hazard |
- + |
+ + |
0 - |
|
Suppression Difficulty |
- - |
+ + |
0 0 |
|
Exposure |
- + |
+ 0 |
+ - |
|
Expected Costs and Losses |
- 0 |
+ + |
0 - |
Taken together, the various factors indicate that the least desirable pattern is the mixed-dispersed arrangement of varying lot sizes. It intersperses a variety of fire environments, increases the edge between them, and makes both prefire and suppression activities difficult. At the other end of the spectrum, a mixed-clustered design offers opportunities to reduce ignitions and decrease fuel continuity, while exposing fewer houses than does the uniform 2-acre pattern. The uniform 2-acre pattern offers some benefit in terms of reduced hazard and improved access, but the greater number of houses outweighs this benefit in any high fire threat environment-independent of mitigation actions-in all but initial attack fire scenarios.