To be able to respond to vulnerability at the urban or individual scale, policy makers and persons alike must be able to understand it. This depends on assumptions and agreement on the context in which vulnerability is applied. Recent literature related to flood vulnerability discusses vulnerability of built systems (e.g. Aroca-Jimenez et al. 2017; Chang and Huang, 2015; Cutter, 2008; Sadeghi-Pouya et al., 2017; Van, 2016), economic systems (e.g. Akukwe et al., 2015; Borden et al., 2007; Cutter, 2008; UNESCO; Van, 2016), environmental systems (e.g. Balica et al., 2012; Chang and Huang, 2015; Rao, 2005; Silva et al. 2016; UNESCO; Zanetti et al., 2016), infrastructural systems (e.g. Aroca-Jimenez et al., 2017; Borden et al., 2007; Cutter, 2008; Silva et al., 2016; UNESCO; Van, 2016), institutional systems (e.g. Aroca-Jiminez et al., 2017, Balica et al., 2012; Cutter, 2008; Sadeghi-Pouya, 2017; Silva et al., 2016; UNESCO), and social systems (e.g. Akukwe et al., 2015; Aroca-Jimenez et al. 2017; Balica et al., 2012; Bathi and Das, 2016; Cançado et al., 2008; Fernandez et al., 2016; Garbutt et al., 2015). Thinking of vulnerability in terms of each of these domains can help decision makers better plan for and respond to extreme flood events.

The discussion of vulnerability as a quantifiable phenomenon has become the topic of research over the past 40 years in the United States. Hundreds of composite indices of multi-hazard vulnerability, resiliency, and risk have emerged globally (Beccari, 2016 Table 3.1), and many others still focused specifically on flood hazards. Flood-specific vulnerability indices were identified in the literature using Google Scholar and through cross-referencing bibliographies of known flood indices. A sample of 40 recently-created flood indices were identified and are included in Table 3.1. These flood vulnerability models were classified in terms of the domains of focus (i.e. social, environmental, institutional, economic, infrastructural, and built environment), input indicators, combinatory methods, spatial scale, and area of interest. Following the definition of vulnerability proposed above, each indicator was further classified in terms of its relation to exposure, susceptibility, and resilience. This classification exercise provides a cross-study summary of the components of vulnerability to floods and provides a basis for critiquing and creating a composite index.