Available at: https://digitalcommons.calpoly.edu/theses/1444
Date of Award
MS in Forestry Sciences
Natural Resources Management
Dr. Christopher Dicus
Since 1990, thirteen fires over 100,000 acres in size have burned in California seven of which were recorded to be some of the most destructive wildfires of all time (California Department of Forestry & Fire Protection 2013). To aid the development of policy that reduces the destruction caused by wildfires, it is important to evaluate how risk changes through time in communities that are expanding into fire-prone areas. The objective of this study is to discover how the likelihood of structural loss is changing in WUI as newer; more fire resilient structures replace older structures on the edges of the WUI.
Geographical Information Systems and remote sensing techniques were used to observe changes in urbanization, structural materials, housing density and defensible space over time in the communities of Rancho Santa Fe, Ramona and Julian in San Diego County. Fire Risk ratings were calculated using the equation Fire Risk= Hazard – Mitigation. Mitigation scores for each structure were informed using a binary logistic regression of variables influencing home loss in the Witch Creek Fire. Fire Risk Ratings were given to the 11,747 structures in the three communities for the years 2005, 2009, 2010 and 2012.
The study found that the initial 0-1.5m zone around the home is the most critical for defensible space. In this zone, increased tree cover increases the odds of structure loss by over double that of grass cover.
In Rancho Santa Fe and Julian, the majority of very high risk homes were located in high income communities despite moderate mitigation due to very high fire hazard levels. In Ramona most very high fire risk homes were located in lower income areas due to poor mitigation levels. Rancho Santa Fe and Julian decreased their fire risk over the 7 year study period with improved mitigation, Rancho Santa Fe improved the most (1.7% decrease in Very High and High risk homes). The proportion of very high fire risk homes increased in Ramona by .5% over the 7 year study period.
Development on the outskirts of the WUI could increase the risk of the overall community if proper construction standards are not met and defensible space is not implemented. If fire resistant communities are constructed and maintained to high standards of defensible space, they could potentially provide a buffer for older high fire risk homes.