Flooding disasters are on the rise: Here’s how to proactively prepare

In recent years, localities have seen an increasing number of flood events. This summer alone, we’ve seen massive impacts from Hurricane Ida and flash flooding temporarily inundating the streets and subway stations in New York City, carrying cars away in Flagstaff, Arizona and damaging property in Bucks County, Pennsylvania.

This will only get worse with climate change, as precipitation falls in heavier events and sea levels are projected to rise. The impact of flooding on our nation’s communities and infrastructure is an acute concern. For example, in the transportation sector, flood waters can overtop roads, leading to road damage, lane closures and traffic slow-downs, which in turn impacts local economic activity. 

And, the frequency of flooding isn’t slowing down — from 1980 to 2020, inland flooding disasters caused $151 billion in damages nationwide, with severe storms, tropical cyclones and inland flooding standing as the top three most frequent types of natural disaster, according to data from  the National Oceanic and Atmospheric Administration (NOAA).

To prepare for future flooding impacts on infrastructure systems, state and local governments could benefit from two types of analyses: first, quantifying the economic impacts of flooding and second, expanding assessments to identify vulnerable pieces of infrastructure outside of Federal Emergency Management Agency (FEMA) designated flood zones.

Quantifying the economic impacts of flooding to communicate the value of investing in resilience

As a step toward understanding the full range of flood impacts on communities, cities and states as public service providers could quantify the economic impacts of flooding. This analysis would emphasize the importance of uninterrupted infrastructure services due to the large price tag — both to public agencies and the public — associated with infrastructure disruptions.

To begin measuring roadway flooding impacts, the ICF Climate Center analyzed roadway flooding data from the Maryland Department of Transportation (MDOT) State Highway Administration (SHA). This study illustrates the economic impact of flooding on a transportation network and its users.

In Maryland, flooding on the state’s highway system results in an extra 1,582 hours per year spent sitting in traffic, and the costs of these delays is estimated at approximately $15 million per year. Overall, total user delay costs from 2006 to 2020, including passenger and freight delays, boasts a large price tag — exceeding $230 million dollars in economic impacts to the state.

By putting a dollar value on flood impacts, state and local governments can draw attention to the impacts of flooding in their regions, and build a case for additional resources to be allocated toward resilience of transportation and other infrastructure to prevent flooding in the first place.

Flood planning must not only rely on FEMA flood zones  

Flooding affects roadways regardless of whether they’re located in a FEMA-designated flood zone — in fact, a majority of flood incidents (78 percent) in the Maryland study are located outside of the FEMA-designated 500-year flood zones. In the Maryland study, most flooding incidents outside FEMA-designated flood zones are relatively close, however, averaging about 0.31 miles from the flood zone.

Flooding is not limited to mapped FEMA flood zones, although these maps are often the most readily available indicator of areas where infrastructure may be at risk. (The purpose of FEMA flood maps is not to predict the full extent of where flooding will occur, but to provide a resource that states and communities can use when assessing risk and making decisions about where and how to build.)

Alternative tools and approaches exist to more accurately evaluate flooding, especially under changing climate conditions. When conducting flood vulnerability assessments, hydrologic modeling provides a more accurate picture of where flooding may occur. This modeling system offers detailed looks at a location’s hydrologic features, such as groundwater and wetlands, to help predict and manage the potential flow of local water resources. While this method provides more accurate results, it is also more costly.

Instead, state and local governments could use simpler methods to understand inland flooding risks. We’ve seen this approach come to life through our climate resiliency and flood mitigation study with the Southeast Michigan Council of Governments, which used a simplified hydrological modeling approach to understand water flow accumulation and ponding. From there, we used data on elevation and distance to culverts to determine how water may flow and pond in the culvert area.  

Cities and states can evaluate a number of cost-effective strategies to conduct vulnerability assessments. Resources include Flood Factor, a tool used to define cities and states’ past, present and future flood risks. Users can analyze past floods, current risks and future projections based on research from the world’s leading flood modelers.

For coastal flooding, it’s important to consider overall sea-level rise. Some states have already developed more granular, state-specific sea-level rise mapping into their planning, as demonstrated by Oregon’s Coast Atlas exposure inventory and California’s “Our Coast, Our Future” initiative. National tools are also available, such as NOAA Sea Level Rise viewer, which maps an area’s exposure to sea-level rise and coastal flooding impact. 

A road forward

As flooding frequency and intensity increases now and in the future, cities, states and regions across the U.S. must proactively prepare for flooding, especially for long-lived infrastructure. Sea levels are continuing to rise, and coastal areas that have not flooded before may flood in the future. 

Flooding has taken priority on a national scale, as seen from President Biden’s recent meetings with FEMA’s climate and homeland security teams ahead of the 2021 hurricane season. The administration announced it is directing $1 billion in funding for communities, states and local governments into pre-disaster mitigation resources to help prepare for extreme weather events in the future. Conducting economic assessments and refining information on vulnerability to flooding can only help cities and states make the case for being a recipient of this funding. 

As such, cities and states have these two steps they could take to advance their planning for flood resilience — quantify the economic impacts and refine their understanding of areas of potential flooding.

Cassandra Bhat is a director of climate resilience at global consultancy firm ICF. 

Angela Wong is a climate resilience consultant at ICF.

Brenda Dix is a director of climate resilience at ICF.