Flood exposure and social vulnerability in the United States

Disasters, 2008

Studies on the impacts of hurricanes, tropical storms, and tornados indicate that poor communities of colour suffer disproportionately in human death and injury. 2 Few quantitative studies have been conducted on the degree to which flood events affect socially vulnerable populations. We address this research void by analysing 832 countywide flood events in Texas from 1997-2001. Specifically, we examine whether geographic localities characterised by high percentages of socially vulnerable populations experience significantly more casualties due to flood events, adjusting for characteristics of the natural and built environment. Zero-inflated negative binomial regression models indicate that the odds of a flood casualty increase with the level of precipitation on the day of a flood event, flood duration, property damage caused by the flood, population density, and the presence of socially vulnerable populations. Odds decrease with the number of dams, the level of precipitation on the day before a recorded flood event, and the extent to which localities have enacted flood mitigation strategies. The study concludes with comments on hazard-resilient communities and protection of casualty-prone populations.

Proceedings of the National Academy of Sciences, 2021

Significance Flooding remains one of the costliest natural disasters globally. Perceptions of—and strategies for mitigating—riverine flooding risk vary both within and across communities, yet this is often overlooked in formal planning efforts. We fit a sociohydrologic model to 50 US metropolitan areas to understand divergent community risk behaviors. We identified two archetypes: “risk-enduring” communities with lower flood defenses and longer memory of past floods and “risk-averse” communities with higher defenses but shorter memory. Behaviors were correlated with streamflow conditions, local dam heights, and the proportion of White to non-White residents. Our findings highlight a potential awareness of local hydrology that may drive perceptions of risk as well as racial inequity in flood exposure and resilience within the United States.

Annals of the American Association of Geographers, 2017

This article conducts a national, county-based assessment of the changes in population and urban areas in highrisk flood zones from 2001 to 2011 in the contiguous United States. The U.S. Federal Emergency Management Agency's (FEMA) 100-year flood maps, land cover data, and census data were used to extract the proportion of developed (urban) land in flood zones by county at the two time points, and indexes of difference were calculated. Local Moran's I statistic was applied to identify hot spots of increase in urban area in flood zones, and geographically weighted regression was used to estimate the population in flood zones from the land cover data. Results show that in 2011, an estimate of about 25.3 million people (8.3 percent of the total population) lived in high-risk flood zones. Nationally, the ratio of urban development in flood zones is less than the ratio of land in flood zones, implying that Americans were responsive to flood hazards by avoiding development in flood zones. This trend varied from place to place, however, with coastal counties having less urban development in flood zones than the inland counties. Furthermore, the contrast between coastal and inland counties increased between 2001 and 2011. Finally, several exceptions from the trend (hot spots) were detected, most notably in New York City and Miami, where significant increases in urban development in flood zones were found. This assessment provides important baseline information on the spatial patterns of flood exposure and their changes from 2001 to 2011. The study pinpoints regions that might need further investigations and better policy to reduce the overall flood risks. Key Words: climate change, flood exposure, flood zone, natural hazard, urban development.

Scientific Reports

Flash flood is among the most catastrophic natural hazards which causes disruption in the environment and societies. Flash flood is mainly initiated by intense rainfall, and due to its rapid onset (within six hours of rainfall), taking action for effective response is challenging. Building resilience to flash floods require understanding of the socio-economic characteristics of the societies and their vulnerability to these extreme events. This study provides a comprehensive assessment of socio-economic vulnerability to flash floods and investigates the main characteristics of flash flood hazard, i.e. frequency, duration, severity, and magnitude. A socio-economic vulnerability index is developed at the county level across the Contiguous United States (CONUS). For this purpose, an ensemble of social and economic variables from the US Census and the Bureau of Economic Analysis were analyzed. Then, the coincidence of socio-economic vulnerability and flash flood hazard were investigated...

Sustainable Cities and Society, 2024

Extracting baseline information on flood exposure and its temporal evolution is essential to formulate flood risk reduction strategies. At present, comprehensive, long-term spatial-temporal flood exposure research in the United States is lacking. The objective of the study is to evaluate county-wide flood exposure in the US and unravel its spatial-temporal dynamics from 2001-2019 to answer three research questions via hypothesis testing. First, how have human settlement areas exposed to flood threats in the US changed over the past two decades? Second, has the occurrence of floods and their resulting damage influenced the growth of developed areas in flood zones? Third, do disparities exist in the sensitivity to flood threats among urban-rural communities? Results show that the overall rate of development in flood zones in the contiguous United States has steadily decreased from 2001 to 2019. The Local Moran's I analysis discovers pockets of emerging, expanding, shrinking, and changing clusters of communities that show a rapid increase or decrease of developed areas within flood zones over time. Most counties that experienced more frequent flooding events demonstrate greater responsiveness to flood hazards by avoiding development in flood zones. Finally, urban communities exhibit a higher exposure and sensitivity to flood hazards compared to rural areas.

Journal of Flood Risk Management, 2013

While flood risk management planning in the United States has focused on flood control structures designed to protect the economic value of property, it has consistently undervalued other social impacts associated with flooding. The US Army Corps of Engineers (USACE) recently initiated research aimed at understanding how to incorporate social characteristics into the measures currently utilised in flood control project evaluation and consideration. This paper proposes a methodology for incorporating a known measure of social vulnerability, the Social Vulnerability Index (SoVI), into USACE civil works planning. Using the USACE South Atlantic Division as the study area, this paper evaluates eight different variations of the social vulnerability metric and their potential deployment in USACE projects. Each formulation is compared with the original-computed SoVI as a means to test its spatial and statistical sensitivity, including an assessment of each variant's robustness, reducibility, scalability, and transferability. Results indicate that while it is possible to create simplified, yet robust, versions of SoVI for individual places, such 'lite' metrics tend to fall short in areas of scalability and transferability in relation to the original SoVI formulation. How the impacts of storms and floods on vulnerable populations were not only overlooked, but severely underestimated, is one of the many lessons learned from Hurricanes Katrina and Rita (IPET, 2006).

Natural Hazards, 2020

Flooding exacerbated by climate change has resulted in more mandatory community participation in the Federal Emergency Management Agency (FEMA) National Flood Insurance Program (NFIP). The purpose of this research is social regulatory floodplain criteria that may have an impact on various socioeconomic factors at the county and sub-county level. Updated mapping can result in widespread changes to the NFIP Special Flood Hazard Area, while no socioeconomic vulnerability assessments are completed before changes in risk designation or subsidy elimination occurs. These changes can result in additional compulsory flood insurance policies, heightened policy costs, and ultimately produce socioeconomic barriers for lowerincome residents. The objectives include demonstrating the potential nationwide implications of increasing community risk with these changes to national policy through a case study from Ada County, Idaho where FEMA began updating the floodplain maps in 2015. Ada County was chosen for being reflective of other communities that may be suffering similar impacts from NFIP policy. A sequential explanatory mixed-methods approach was employed using semistructured interviews, spatial analysis, and the Spatially Explicit Resilience-Vulnerability (SERV) model to assess potential community impacts. Results indicate increased vulnerability in the revised floodplain. Total annual sales volume, employee numbers, industry sectors, and overall community vulnerability are higher in the revised floodplain. Interviews with community leaders corroborated these results. This case study provides a foundation for further research on the impacts of flood insurance on communities across the United States while discussing the social injustice of a national program that is likely promoting the upward distribution of wealth county by county.

Sustainable Cities and Society

As urban populations continue to grow through the 21st century, more people are projected to be at risk of exposure to climate change-induced extreme events. To investigate the complexity of urban floods, this study applied an interlinked social-ecological-technological systems (SETS) vulnerability framework by developing an urban flood vulnerability index for six US cities. Indicators were selected to reflect and illustrate exposure, sensitivity, and adaptive capacity to flooding for each of the three domains of SETS. We quantified 18 indicators and normalized them by the cities' 500-yr floodplain area at the census block group level. Clusters of flood vulnerable areas were identified differently by each SETS domain, and some areas were vulnerable to floods in more than one domain. Results are provided to support decision-making for reducing risks to flooding, by considering social, ecological, and technological vulnerability as well as hotspots where multiple sources of vulnerability coexist. The spatially explicit urban SETS flood vulnerability framework can be transferred to other regions facing challenging urban floods and other types of environmental hazards. Mapping SETS flood vulnerability helps to reveal intersections of complex SETS interactions and inform policy-making for building more resilient cities in the face of extreme events and climate change impacts.

JAWRA Journal of the American Water Resources Association, 2018

With growing urban populations and climate change, urban flooding is an important global issue, even in dryland regions. Flood risk assessments are usually used to identify vulnerable locations and populations, flooding experience patterns, or levels of concern about flooding, but rarely are all of these approaches combined. Furthermore, the social dynamics of flood concerns, exposure, and experience are underexplored. We combined geographic and survey data on household‐level measures of flood experience, concern, and exposure in Utah's urbanizing Wasatch Front. We asked: (1) Are socially vulnerable groups more likely to be exposed to flood risk? (2) How common are flooding experiences among urban residents, and how are these experiences related to sociodemographic characteristics and exposure? and (3) How concerned are urban residents about flooding, and does concern vary by exposure, flood experience, and sociodemographic characteristics? Although floodplain residents were mor...

International Journal of Disaster Risk Reduction, 2019

Vulnerability studies often measure the risk that influences a system's ability to react during the occurrence of a hazardous event. Risk is generally associated with the physical, social, and economic aspects of the system. Climate-related hazards such as floods involve an additional spatial dimension, however. It is challenging combining social and geophysical vulnerabilities to model their interrelations to overall flood vulnerability. This study proposes the partial least squares structural equation model (PLS-SEM) with several latent variables of geographical characteristics of houses and socioeconomic dimensions of households representing flood vulnerability. The former includes GIS/remote sensing data, while the latter comprises household surveys. The results indicate social indicators get contribution mainly from direct effects of spatial neighborhoods and socioeconomic conditions, and indirect effects of land tenure and demographics, with path coefficients equal to 0.47, 0.42, 0.83, and 0.61, respectively, all significant at the p < 0:0001 level. Overall, the goodness of fit equals 0.72 indicates good explanatory power of the model. We conclude that the PLS-SEM successfully incorporated the combined vulnerability from social and geographical factors. The SEM framework allows integrative assessing vulnerability variables from different disciplines, formats, and scales, and thus, offers an opportunity for creating more tailored policies to combat hazards.