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Thoughts From Engineers: Where the Water Will Go

Chris Maeder on November 28, 2022 - in Articles, Column

The local waterfront pub you’ve been in the habit of visiting for burgers and fries on Friday night is very likely to be flooded several times a year by the year 2050. Moreover, if past development patterns are anything to go by, this historic eatery probably will be in the same risky spot 10 years from now, albeit flood-weary and on shaky financial ground. Part of a long-lived and much-loved community—complete with housing, school and commercial districts—it has hung on for years despite a flood risk that grows every year. The neighborhood is the product of community resolve—and government support—to stay put, notwithstanding the intensity of recurring rain events or the severity of the next storm.

This hypothetical neighborhood pub represents a universal scenario that’s likely to become all too familiar in the years ahead. According to the authors of the article “Inequitable patterns of U.S. flood risk in the Anthropocene” (go.nature.com/3T3Y9IW), which appeared in the February 2022 issue of Nature Climate Change, scientists identify vast stretches of coastal and inland shoreline that can expect higher flood risk in coming decades along with the communities that are settled there—stuck in the flooding crosshairs, quite often due to insufficient information, few adaptative measures in place, lack of personal resources or a blend of the above.

The study underlines that not only do existing flood maps in many cases not give adequate notice of present and future flood hazards, but current policy in many regions of the United States effectively places people in harm’s way and promotes risky development patterns. According to the model used in this research, millions of people—mostly in poorer communities—are likely to experience regular flooding as warming trends ramp up in coming years.

Flood Maps from Another Time

The massive flooding associated with the extreme storm events of recent years established that existing flood maps frequently don’t capture the extent of modern-day flood risks. The study authors point out from their research that many flood models in use today are overly simplistic and don’t capture the many complex physical dynamics at work with a warming climate. They note that the maps generated by the Federal Emergency Management Agency (FEMA) typically include high-quality terrain and survey data, but simulated flood frequencies are limited, and there’s no mandate to integrate climate considerations. Moreover, since FEMA’s national flood mapping program started in 1967, only one third of all rivers in the United States are mapped. Of these, only a quarter have been updated per a five-year federal revision mandate.

The hydrodynamic flood model presented in the aforementioned article compensates for these limitations with use of 3-meter-spatial-resolution terrain and factors related to climate change and flood hazards: present and future sea-level rise, shifting weather patterns, and other critical parameters. Other data are integrated into this analysis (e.g., the National Structure Inventory, U.S. Army Corps of Engineers structure vulnerability metrics, demographic data, etc.), which helps assess the exposure and vulnerability of buildings and specific communities to flood hazards today and in the decades ahead.

Future U.S. Flood Losses and Communities at Risk

Their analysis projects that annualized U.S. flood losses will increase from an average of $32.1 billion today to $40.6 billion by 2050 (in present-value dollars), representing a 26-percent increase in flood risk within a relatively short period of time. This is a near-certain climate-generated impact that will occur even if carbon emissions were to vanish tomorrow. Their model shows clusters of future hotspots that are both troubling and informative. The analysis identifies zones in densely populated coastal areas and Appalachia that will continue to be at high risk. Hurricanes will continue to intensify coastal surges affecting Virginia, the Carolinas and Florida. Inland areas also will be affected, particularly in the Northeast, with more-intense rainfall projected.

The population presently at greatest risk of flooding is predominantly White and poor, but this is likely to change by 2050, with mainly Black and poorer populations constituting the largest socioeconomic group with increased flooding impact risk. Census tracts with the highest proportions of Black populations, many of which are in the Deep South, would experience a 20-percent increase in flood-risk exposure by 2050. Census tracts with the lowest Black populations would see a minimal increase in flood risk within that same timeframe.

Risks of ‘Staying the Course’

The risk to human life and property due to climate change is one of the most-pressing issues of our time. Look no further than the shredded remains of Florida’s once-thriving west-coast waterfront communities or the high number of fatalities brought about by Hurricane Ian for a glimpse of crises to come. The study’s most-important point, however, is that were it not for the constant migration to and settlement of our increasingly hazardous coastlines and high-risk inland areas, we would not see the same risk exposure that’s currently projected. This pattern—even assuming stable climate conditions—means we increase our exposure to flood risk by 73 percent, which far exceeds the risk from climate change alone.

The process of delineating flood hazards and developing flood maps is a complex and controversial matter, and it has been covered extensively elsewhere. Suffice to say that plenty of factors—from protecting property value to preserving the municipal tax base to the cost of insurance and expensive building code retrofits—function to chip away at proposed flood hazard zones. By one account (bit.ly/100yrFloodOrigin), the equivalent of roughly 41 miles of flood-prone shoreline was eliminated from a proposed flood map due to appeals alone. However, federal programs to promote climate adaptation and community resilience are starting to ramp up to meet the challenge and support the sticky decisions that are necessary and urgent. It’s a tough sell. Sometimes nothing is quite as strong as a person’s identification with a specific place or community—the favorite burger joint or the place you’ve called home for decades. The idea of starting over becomes unthinkable (bit.ly/ShouldWeRebuild). 

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About Chris Maeder

Chris Maeder, P.E., M.S., CFM, is engineering director at CivilGEO Inc.; email: [email protected].

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