Community clusters of tsunami vulnerability in the US Pacific Northwest

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 17; pp. 5354 - 5359
• Main Authors: Wood, Nathan J., Jones, Jeanne, Spielman, Seth, Schmidtlein, Mathew C.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 28.04.2015; National Acad Sciences
• Subjects: Cluster analysis; Earthquakes; Hazards; Physical Sciences; Risk assessment; Social Sciences; Sustainability; Tsunamis; United States; United States > US; Pacific Northwest; INE, Pacific, Cascadia Subduction Zone; INE, USA, California; USA, Pacific Northwest; INE, USA, Pacific Northwest; INE, USA, Washington; evacuation; tsunami; vulnerability; hazard; disaster
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1420309112

Many coastal communities throughout the world are threatened by local (or near-field) tsunamis that could inundate low-lying areas in a matter of minutes after generation. Although the hazard and sustainability literature often frames vulnerability conceptually as a multidimensional issue involving exposure, sensitivity, and resilience to a hazard, assessments often focus on one element or do not recognize the hazard context. We introduce an analytical framework for describing variations in population vulnerability to tsunami hazards that integrates ( i ) geospatial approaches to identify the number and characteristics of people in hazard zones, ( ii ) anisotropic path distance models to estimate evacuation travel times to safety, and ( iii ) cluster analysis to classify communities with similar vulnerability. We demonstrate this approach by classifying 49 incorporated cities, 7 tribal reservations, and 17 counties from northern California to northern Washington that are directly threatened by tsunami waves associated with a Cascadia subduction zone earthquake. Results suggest three primary community groups: ( i ) relatively low numbers of exposed populations with varied demographic sensitivities, ( ii ) high numbers of exposed populations but sufficient time to evacuate before wave arrival, and ( iii ) moderate numbers of exposed populations but insufficient time to evacuate. Results can be used to enhance general hazard-awareness efforts with targeted interventions, such as education and outreach tailored to local demographics, evacuation training, and/or vertical evacuation refuges. Significance We present an analytical framework for understanding community-level vulnerability to tsunamis that integrates population exposure, demographic sensitivity, and evacuation potential.We identify three types of communities along the US Pacific Northwest coast that are directly threatened by tsunamis associated with a Cascadia subduction zone earthquake: ( i ) demographically diverse with low numbers of exposed people, ( ii ) high numbers of exposed populations but sufficient time to evacuate, and ( iii ) moderate numbers of exposed populations but insufficient time to evacuate. This approach is a significant advance over current practice because traditional measures of social vulnerability do not relate population structure to specific hazard characteristics. Results help managers to develop risk reduction strategies that are tailored to local conditions and needs.