Community risk due to wildland urban interface fires: a top-down perspective
Chulahwat, Akshat, author
Mahmoud, Hussam, advisor
Ellingwood, Bruce, committee member
van de Lindt, John, committee member
Stevens-Rumann, Camille, committee member
Recent wildfire events, in the United States and around the world, have resulted in thousands of homes destroyed and many lives lost, leaving communities and policy makers, with the question as to how to manage wildfire risk. Wildland urban interface fires have demonstrated the unrelenting destructive nature of these events and signify the need to address the problem. This is particularly important given the prevalent trend of increased fire frequency and intensity. Current approaches to managing wildfires focus on fire suppression and managing fuel build-up in wildlands. Frequent suppression of small scale fires has led to the absence of a natural reduction mechanism, which in turn, results in low frequency high intensity fires. This phenomena has been termed as the Wildfire paradox and it reinforces the ideology that wildfires are inevitable and are actually beneficial; therefore focus should to be shifted towards minimizing potential losses to communities. However, reliance on these strategies alone has clearly proven inadequate. This requires the development of vulnerability-based frameworks that can be used to provide holistic understanding of risk. Mitigation strategies geared towards complete containment of wildfires within the wildlands are unrealistic. Therefore, the primary goal has to be on making communities resilient, with the purpose of minimizing potential losses. There is a paucity of information regarding the interplay between communities and wildfires. Unlike other hazards, for which there exists significant knowledge base, quantification of WUI fires is still an unanswered question for us. To better understand what factors govern the impact of WUI fires, tools to assess and quantify the risk of wildfires to communities are required. In this study, a probabilistic approach for quantifying community vulnerability to wildfires by applying concepts of graph theory is devised. A directed graph is developed to model wildfire inside a community by incorporating different fire propagation modes. Four modes are considered in this study - Convection, Radiation and Embers, and individual ignition models for each are formulated. Through these modes the graph model accounts for relevant community-specific characteristics including wind conditions, community layout, individual structural features, and the surrounding wildland vegetation. The graph model is then used to evaluate vulnerability of each component of the community using shortest path algorithms. The framework is utilized to study the infamous 1991 Oakland fire in an attempt to unravel the complexity of community fires. Centrality measures from graph theory are used to identify critical behavior patterns and evaluate the effect of fire mitigation strategies. Using the vulnerability framework developed, the risk of communities is further quantified. Risk is generally defined by three components - (1) Hazard intensity (2) Degree of exposure and (3) Exposed elements. In context of wildfires, the risk is formulated by combining the following three components - probability of wildland ignition, probability of fire reaching the community and vulnerability of community. Four different communities across the United States are selected and risk analysis is conducted for the months May-September to understand the correlation between community risk and community characteristics. Unlike current practice, the results are shown to be community-specific with substantial dependency of risk on meteorological conditions, environmental factors, and community characteristics and layout. For the final part of this study, an intervention optimization is formulated and applied to the four communities to observe the effect of different intervention measures on community risk. The findings show the need for exploring unique viable solutions to reduce risk for communities independently, as opposed to embracing a generalized approach, which is currently the case.
Includes bibliographical references.
Includes bibliographical references.