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Social vulnerability is an essential concept to understand the extent to which human society is vulnerable to natural disasters (Cutter & Finch, 2008). As the human population has experienced extraordinary growth, redistribution, and compositional change across the world, both the social and natural environments of the world have been significantly altered. As the result, the anthropogenic factors, such as deforestation, land use change, and excessive emission of greenhouse gases have become the major drivers that accelerate the global climate change (National Academies of Sciences, 2016). The changing global climate is likely to increase the intensity and severity of natural hazards – such as heat waves, droughts, wildfires, floods, and tropical cyclones (Van Aalst, 2006). Many rapidly growing human communities in the United States are increasingly exposed and vulnerable to the natural hazards (Flanagan, Gregory, Hallisey, Heitgerd, & Lewis, 2011). Assessing the extent to which the United States is vulnerable to natural hazards in space and over time is fundamental to prepare for, counteract, and mitigate potential damages from natural hazards (Cutter, 1996; Van Aalst, 2006). This study investigates how social vulnerability of counties in the United States has evolved in space and over time from 1970 to 2010.
It is well known that the severity of the aftermath of natural hazards is not only directly affected by the geophysical characteristics of the hazard events, but also compounded by the social characteristics of the affected populations (Cutter, 1996; Tobin & Montz, 1997). The at-risk populations of different social characteristics can disproportionately magnify or attenuate the impacts of natural hazards as they have differential capacity to adapt to and recover from exogenous perturbations (Adger, 2006; Cutter, 2001; Turner et al., 2003). Socially vulnerable populations are likely to suffer greater disruption in the wake of natural hazards due to the lack of resources and coping capacity (Cutter, 2001, 2009; Wisner, Blaikie, Cannon, & Davis, 2004). As such, natural disasters are an outgrowth of social vulnerability and can be considered socially produced, or “unnatural” (Laska & Morrow, 2006; Logan, 2009; N. Smith, 2006; Wisner et al., 2004). Assessing social vulnerability is fundamental to understand how human society is vulnerable to natural hazards and can be prepared with preventive mitigation strategies.
Social vulnerability is often assessed by social vulnerability index (SoVI), which was first introduced by Cutter, Boruff, and Shirley (2003), and has since been widely used to assess the relative level of social vulnerability at various geographic scales based upon the underlying demographic and socio-economic characteristics. The SoVI is a composite index that can help better understand the cross-sectional and spatial variation of social vulnerability. Following Cutter et al. (2003)’s approach, many studies have used SoVI to measure the spatial distribution of social vulnerability to all natural hazards or specific hazard events such as floods, tsunami, sea-level rise, and hurricanes (Burton & Cutter, 2008; Flanagan et al., 2011; Myers, Slack, & Singelmann, 2008; Rufat, Tate, Burton, & Maroof, 2015; Rygel, O’sullivan, & Yarnal, 2006; Wang & Yarnal, 2012; Wood, Burton, & Cutter, 2010; Wu, Yarnal, & Fisher, 2002; Yoon, 2012; Zahran, Brody, Peacock, Vedlitz, & Grover, 2008). In particular, mapping SoVI is very often used to reveal the regional discrepancy and spatial variation of social vulnerability (Cutter et al., 2003; Cutter & Finch, 2008; D. King & MacGregor, 2000; Morrow, 1999).