A national look at the causes and impacts of urban flooding

A National Challenge

In 2016, the Center for Disaster Resilience at the University of Maryland and Center for Texas Beaches and Shores at Texas A&M University, Galveston Campus initiated a joint study to identify the principal causes of flooding, determine the extent and consequences of urban flooding in the United States, and explore what actions might be taken to mitigate this flooding in the future. Center researchers analyzed available data concerning urban flooding, surveyed municipal flood and stormwater managers, and met with professionals whose disciplines intersect with urban flooding at the local, state, and national level.

The research team's findings affirm that urban flooding is a national and significant source of economic loss, social disruption, and housing inequality. This report presents the full results of the study, addresses governance issues that affect urban flood risk reduction, examines critical challenges, and offers recommendations for actions.

In much of the United States, urban flooding is occurring and is a growing source of significant economic loss, social disruption, and housing inequality. Extensive suburban development that creates higher flood flows into urban areas, aging and frequently undersized infrastructure in older sections of communities, an inability to maintain existing drainage systems, increases in intense rainfall events, and uncoordinated watershed management all contribute to these increases in urban flooding.
The growing number of extreme rainfall events that produce intense precipitation are resulting in—and will continue to result in—increased urban flooding unless steps are taken to mitigate their impacts. The 2017 National Climate Assessment concluded that “heavy downpours are increasing nationally, especially over the last three to five decades…[and that]… increases in the frequency and intensity of extreme precipitation events are projected for all U.S. regions.”
Communities across the nation are facing similar challenges with urban flooding. However, the unique hydrological, physical, and social characteristics of these communities mean solutions are best developed locally. While the magnitude of urban flooding challenges merit federal guidance and support when needed, responsibilities must rest primarily at the local level.
While primary responsibility for mitigation of urban flooding rests with local governments, the division of responsibilities among federal, state, regional, local, and tribal governments for urban flood and stormwater management are not clearly defined. Responsibilities are diffused and lack the collaboration and coordination necessary to address the technical and political challenges that must be faced.
Many of the urban wastewater and stormwater systems that provide the backbone of urban flood mitigation are in poor condition and—in some locations—are inadequate and in need of strong support. The human and fiscal resources necessary to address urban flooding are not generally available at the levels required.
At the federal level, there is no agency charged with oversight of federal support of urban flood mitigation-related activities. While primary responsibility for urban flood mitigation rests at the local level, the federal government is already operating programs for riverine and coastal flood risk reduction and stormwater management; these programs are inextricably linked to urban flooding.
The economic and social impacts of urban flooding are generally not well known and understood by many public officials and the unaffected public. Social vulnerabilities and inequities in disaster recovery for low-income populations are not being fully addressed.
Governments, at all levels, have not provided effective means to communicate risks to those in urban flood-prone areas. A significant number of these areas are not identified by maps produced under the Federal Emergency Management Agency National Flood Insurance Program, and actions by those responsible for urban flood mitigation are needed to delineate these areas. Communication of flood risk is often seen by public officials and developers as a negative.
Many homeowners and renters living and working in areas affected by urban flooding do not understand that they can take steps to significantly reduce their property’s vulnerability, and many lack the resources and support necessary to carry out such actions. Information on how a resident can reduce their property’s flood risk is not accessible or well-articulated.
Data—covering insurance claims, assistance, and loans for flood mitigation—are not easily available or shared with local decision-makers, researchers, and the residents themselves. More accessibility and availability of data is critical to effective response, recovery, and long-term mitigation of flood events. This data must be provided in an easily interpreted and spatially identifiable format.

Governors, tribal leaders, and regional and municipal officials should review the current responsibilities for oversight of urban flooding mitigation, as well as flood, water, wastewater, and stormwater management in their jurisdictions; provisions, as appropriate, should be made to ensure efficient and effective multi-jurisdictional planning and operation of these activities and services on a geographic scale that matches the problems being addressed.
The administration, in coordination with Congress, should convene a forum of representatives from state and local governments, Indian tribes, nongovernmental organizations, and the public to develop a national “suite of actions” to mitigate urban flooding and identify responsibilities at each level of government.
The administration, in coordination with Congress, should assign one federal agency to provide interim oversight of federal support of urban flood mitigation activities, the development of the national forum, and the preparation of a post-forum report for the administration, Congress, the states, municipalities, and tribes.
Attention should be given at all levels of government to ensure that efforts to mitigate urban flooding reach areas that have the highest risk of flooding and cross all economic and social levels and that locally supported steps are taken to incentivize individual homeowner mitigation efforts.
In coordination with ongoing efforts to ensure that those at risk of flooding are aware of their vulnerabilities, FEMA, USACE, NOAA, USGS, EPA, and HUD, in collaboration with urban flood communities, should integrate urban flood risk communication outreach into their ongoing programs for riverine and coastal flooding and ensure that analysis of future conditions should include the impacts of climate and weather and future development.
States should consider integrating urban flood risk communication, mapping, and risk disclosure measures into real estate transactions in urban flood areas.
The Congress and the administration, in coordination with state governors, regional, local, and tribal officials, should develop appropriate mechanisms at the federal, state, and local level to fund necessary repairs, operations, and upgrades of current stormwater and urban flood-related infrastructure.
Congress should direct the administration to establish a risk identification grant program that enables communities to develop effective means of identifying the risks they face from urban flooding.
The administration should support continued research into urban flooding to ensure that the full extent of the threat is identified and that steps are taken to formulate solutions to policy and technical issues.

Authors

Gerald Galloway

Gerald E. Galloway, PE, Ph.D., is a Glenn L. Martin Institute Professor of Engineering in the Department of Civil and Environmental Engineering at the University of Maryland, a Faculty Fellow of the Hagler Institute for Advanced Study Texas A&M University, and a visiting professor at the Texas A&M Galveston Campus. His teaching and research focus is on water resources policy, resilience, and disaster risk management under climate change. He serves as a consultant to several international, federal, state, and non-governmental agencies and has been involved in water projects in the United States, Europe, Asia, and South America. In 1993, he was assigned to the White House to lead the study of the Great Mississippi Flood of that year. He is currently a member of the Maryland Coast Smart Council. In 2014, he was appointed chair of an international panel of experts to examine the flooding threats to Florence, Italy and by the government of Singapore to a panel of experts advising on sea- level rise challenges. He is an elected member of the National Academy of Engineering, the National Academy of Public Administration, and the National Academy of Construction and a 38-year veteran of the U.S. Army who retired as a Brigadier General and Dean (Chief Academic Officer) at the U.S. Military Academy at West Point.

Sam Brody

Samuel D. Brody is a regents professor and holder of the George P. Mitchell ’40 Chair in Sustainable Coasts in the Departments of Marine Sciences and Landscape Architecture and Urban Planning at Texas A&M University. He is the director of Center for Texas Beaches and Shores and the lead technical expert for the Governor’s Commission to Rebuild Texas. Brody’s research focuses on coastal environmental planning, spatial analysis, flood mitigation, climate change policy, and natural hazards mitigation. He has published numerous scientific articles on flood risk and mitigation and recently authored the book, Rising Waters: The causes and consequences of flooding in the United States, published by Cambridge University Press. Brody teaches graduate courses in environmental planning, flood mitigation, and coastal resiliency. He has also worked in both the public and private sectors to help local coastal communities adopt flood mitigation plans.

Allison Reilly

Allison Reilly, Ph.D., is an assistant professor in the Department of Civil and Environmental Engineering at the University of Maryland, where she specializes in risk and resilience of infrastructure systems. Her research focuses on characterizing the interplay between infrastructure resilience and individual decision-making. An affiliate of the Center for Disaster Resilience, Reilly is currently leading a three-year project funded by the National Science Foundation to explore and improve infrastructure operator decision-making in the wake of a disaster. Reilly joined the University of Maryland from the Department of Industrial and Operations Engineering at the University of Michigan. She also served as a research analyst for the Homeland Security Studies and Analysis Institute, a federally-funded research and development center in support of the Department of Homeland Security.

Wesley E. Highfield

Wesley Highfield, Ph.D. is an associate professor in the Department of Marine Sciences and associate director of research for the Center for Texas Beaches and Shores at Texas A&M University, Galveston Campus. Highfield’s research is focused on natural hazard impacts and mitigation through interdisciplinary spatial and statistical analytical methods and applications. Most recently, his work has been focused on the impacts of Hurricane Harvey and regional mitigation techniques. Highfield also teaches introductory and advanced geographic information systems to undergraduate and graduate students in the Department of Marine Sciences and is the coordinator for the Marine Resources Management Master’s Program.

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