- 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.
The Growing Threat of Urban Flooding
Released in November 2018, this report offers the first national assessment of the scope and consequences of urban flooding in the United States.
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