Integrated multihazard mapping

A primary goal of the US Disaster Mitigation Act of 2000 is to slow the increase in disaster losses by emphasizing a proactive approach focusing on predisaster hazard mitigation, rather than postdisaster relief. The legislation requires local communities to produce hazard-mitigation plans that include multihazard maps, signifying a de facto prioritization of mitigation dollars on the basis of areas with the greatest vulnerability. However, there is little formal or practical guidance for communities on how to produce such maps. We propose a methodology for hazard-vulnerability assessments using multihazard mapping, where hazard frequency is a measure of risk, historical dollar losses are a proxy for infrastructure impact or exposure, and the Social Vulnerability Index (SoVI) evaluates human vulnerability. Using a test case of one county, Charleston, South Carolina, a geographic information system spatially combined these dimensions of vulnerability across multiple hazards. The resulting maps provide a tool for hazard-mitigation planning, which contains an initial screening element to highlight zones of highest multihazard vulnerability. The approach helps to generate a view of not just what is at risk, but who is at risk, and where, thus enhancing the implementation of targeted impact-reduction strategies. doi:10.1068/b35157 }Corresponding author. guidance for commercial nuclear reactors.Vulnerability analyses stemming from programs such as these have advanced our understanding of specific hazards. However, hazardmitigation and emergency managers aiming to reduce impacts often contend with a range of hazards. A typical output of multihazard mapping initiatives is an atlas depicting the location of individual hazards (FEMA, 1997), but lacking details regarding frequency and severity at the local level. Relatively little work has focused on how to integrate multiple hazards into a comprehensive all-hazards vulnerability analysis at local to regional scales. We demonstrate a geographic information system (GIS)-based methodology for the spatial combination of multiple hazards, based on hazard risk, impacts (or exposure), and social vulnerability. While the basic concept has been elucidated previously (Cutter et al, 2000), the ways in which exposure and impact are measured, coupled with a GIS-based analytical approach, provide a new way to conceptualize the overall hazardousness of a place. We demonstrate the approach using Charleston County, South Carolina as our initial test-bed, but recognize the utility of the approach for other countries in the US as well as other subnational administrative units elsewhere in the world. 2 DMA 2000 vulnerability assessment The DMA 2000 requirements for the content of hazard-mitigation plans are in the US Code of Federal Regulations (CFR, 2002, title 44, part 201, section 6). Among these are descriptions of the type, location, and extent of relevant hazards, and a risk-based characterization of hazard vulnerability. The DMA 2000 vulnerability assessment includes descriptions of the buildings and infrastructure in hazard-prone areas, estimated dollar losses, and information regarding land use and development trends (CFR, 2002). South Carolina implements these requirements in both its state hazard mitigation plan (SCEMD, 2007) and the plans of those counties and communities that it approves. The process generally examines all natural hazards affecting the study area, maps hazard zones and important infrastructure, compiles historical built-environment damages and human injuries and fatalities, and collects basic demographic data. Potential dollar losses are tallied using a combination of statistical analyses of historical losses, and loss-estimation software such as HAZUS (http://www.fema.gov/hazus/), and then ranked by hazard to help prioritize mitigation alternatives. While this procedure is in agreement with the requirements of DMA 2000, it fails to characterize hazard vulnerability in several important ways. First, the geographic locations and extent of a given hazard are portrayed through maps, yet the spatial variation in losses within hazard zones generally is not. Second, the approach proceeds through an analysis of individual hazards, without consideration of the combined effects. Combining hazard zones and impacts across the study area means that mitigation projects could be selected on the basis of rankings of geographic locations susceptible to multiple hazards versus the current prioritization method, which is based largely on the rank order of individual hazards. Third, most of the impacts focus on economic losses to the built environment rather than on the impacts on people, such as injuries or lives lost. This skews mitigation decisions in the direction of infrastructure projects. A more inclusive analysis might suggest nonstructural approaches such as warning systems, evacuation protocols, and outreach programs, which could reduce vulnerability at a lower cost to the community. Finally, the current process is both data and labor intensive, resulting in an excess of resources spent on risk assessment, monies that could easily be spent on future mitigation projects. A screening tool would be useful in this respect, to help focus the hazard risk assessment on the most dangerous hazards and locations. We offer a GIS-based approach to help overcome these shortcomings in the existing hazard-vulnerability assessments. Integrated multihazard mapping 647