Population Evacuation: Assessing Spatial Variability in Geophysical Risk and Social Vulnerability to Natural Hazards Jayajit Chakraborty 1 ; Graham A. Tobin 2 ; and Burrell E. Montz 3 Abstract: Developing an effective evacuation strategy for hurricane zones presents challenges to emergency planners because of spatial differences in geophysical risk and social vulnerability. This study examines spatial variability in evacuation assistance needs as related to the hurricane hazard. Two quantitative indicators are developed: a geophysical risk index, based on National Hurricane Center and National Flood Insurance Program data, and a social vulnerability index, based on census information. These indices are combined to determine spatial patterns of evacuation assistance needs in Hillsborough County, Florida. Four evacuation dimensions are analyzed: population traits and building structures, differential access to resources, special evacuation needs, and a combination of variables. Results indicate that geophysical risk and social vulnerability can produce different spatial patterns that complicate emergency management. Different measures of social vulnerability also confound evacuation strategies and can result in ineffective practices. It is argued that careful consideration be given to the characteristics of local populations. DOI: 10.1061/(ASCE)1527-6988(2005)6:1(23) CE Database subject headings: Evacuation; Emergency services; Geographic information systems; Disasters; Hurricanes. Introduction Hazards researchers from a number of disciplines have turned their attention to issues associated with risk and vulnerability (Blaikie et al. 1994; Bernstein 1998; Kunreuther 1998; Mileti 1999; Cutter et al. 2000; Slovic 2000; Jaeger et al. 2001). Al- though the approaches differ and definitions vary, there has been increasing emphasis on the importance of the intersection of geo- physical conditions and social systems (Liverman 1990; Dow 1992; Montz and Tobin 2003). Geophysical conditions are gener- ally considered to define levels of risk, and the social systems are considered to define variations in vulnerability. Various defini- tions of such terms exist; but for these purposes, hazard is used to denote the overall problem; and a disaster (i.e., an event that has occurred) is defined as some function of geophysical risk and socioeconomic vulnerability (Tobin and Montz 1997). Research to date has focused on enhancing understanding of each sepa- rately and as they may work together to define varying degrees of hazardousness. Although the academic discussion surrounding geophysical risk, socioeconomic vulnerability, and overall haz- ardousness is important, so too is the application of this knowl- edge to particular hazard assessment and management problems. It makes a difference whether risk and vulnerability are being evaluated with respect to land use policies and practices, a medium- to long-term process, or to evacuation planning, usually a short-term need. This research is directed to evacuation plan- ning. The estimation of geophysical risk and vulnerability is prob- lematic, due in part because of a lack of accurate data and because of the way in which available data are used (The Heinz Center 2000). This estimation is particularly challenging in coastal areas where rapid population growth and increasing development com- plicate evacuation planning by necessitating continued revisiting of factors that influence risk and vulnerability. The research pre- sented here approaches these issues by evaluating spatial varia- tions in both geophysical risk and social vulnerability at a specific coastal area and then combining them to assess the overall evacu- ation assistance needs of that location. In doing so, this project is aimed at answering three questions: 1. How does the spatial distribution of socially vulnerable people and structures compare with the spatial distribution of geophysical risk? 2. To what extent does changing the variables that are included alter the overall patterns of social vulnerability and thus of evacuation assistance need? 3. How might the responses to these questions affect emergency management and evacuation planning approaches? The goal of this research, therefore, is to facilitate effective emergency planning for the evacuation of populations in urban- ized coastal areas. Using a geographical information systems (GIS) framework, various geophysical patterns and social vulner- ability indicators are combined to determine the spatial distribu- tion of evacuation assistance needs and explore the answers to these questions, on the basis of a case study conducted in a coastal county: Hillsborough County, Florida. 1 Assistant Professor, Dept. of Geography, Univ. of South Florida, 4202 E. Fowler Ave., SOC 107, Tampa, FL 33620. 2 Professor, Dept. of Geography, Univ. of South Florida, 4202 E. Fowler Ave., SOC 107, Tampa, FL 33620. 3 Professor, Dept. of Geography, P.O. Box 600, Binghamton Univ., Binghamton, NY 13902-6000. Note. Discussion open until July 1, 2005. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on April 12, 2004; approved on July 20, 2004. This paper is part of the Natural Hazards Review, Vol. 6, No. 1, February 1, 2005. ©ASCE, ISSN 1527-6988/2005/1-23–33/$25.00. NATURAL HAZARDS REVIEW © ASCE / FEBRUARY 2005 / 23