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Flood Maps Are Outdated - Here’s How to Fix Them

Emily Heaslip

According to FEMA, 90% of natural disasters in the US involve a flood. As climate change leads to rising sea levels, we expect this percentage to continue to increase. Unfortunately, two recent studies confirm a problem that has long threatened the security of our coasts: flood maps that can help mitigate the risk of flooding are inaccurate and outdated. 

The Department of Homeland Security has been aware of this issue since 2017, when the NRDC reported that 58% of all FEMA flood maps were considered by the Inspector General to be virtually obsolete. This fall, however, two studies show that the problem has persisted. Flood maps are a vital part of community resilience and city planning – without accurate maps, flood warning systems may not have the right data needed to warn communities to evacuate in time. 

Updating flood maps must be a priority – and luckily, moored buoy networks can help collect the data needed to rapidly update these maps and keep our coasts safe. Here’s what is wrong with our existing flood maps, as well as some ways to fix the problem. 

The problem with flood maps

Over time, our flood maps have become dangerously irrelevant. The rapid pace of climate change and sea-level rise has made flood maps a crucial aspect of flood warning systems, but today’s maps are incomplete, inaccurate, and out-of-date.

First, flood maps do not provide a complete picture of our coasts and flood plains. A recent report by the Association of State Floodplain Managers found that FEMA produced flood maps covering only one-third of the nation’s 3.5 million miles of streams and 46% of shoreline.” Less than half of our coasts and other flood-prone areas have been mapped at all by FEMA. 

Of those that have been mapped, the reports are remarkably inaccurate. FEMA’s maps do not account for climate change, according to two studies released this year. Rising sea levels and more intense rain can lead to greater storm surges, and therefore more flooding, but current maps don’t factor in those risks. “FEMA’s flood maps look backward in time and determine the size of the 100-year and 500-year floodplain based on past events,” says the NRDC

FEMA is required to update flood maps every five years. Unfortunately, the updates that are currently implemented are shortsighted – without accounting for higher storm surges and more intense rainfall, communities will underestimate the risk of floods. Worse, for those maps that haven’t been updated, the level of flood risk is considered “unknown.” These blind spots can be devastating to families and towns across the country. 

What are flood maps used for? 

To some extent, there are aspects of natural disasters that are within our control. City planners and community leaders can make decisions that keep people and property out of harm’s way. But, they can only do so when they have the right information, and this is where flood maps come into play. 

“Flood maps are used an estimated 30 million times each year by government agencies, FEMA contractors, lenders, insurance agents, land developers, realtors, community planners, property owners, and others for insurance purposes, land management, mitigation, risk assessment, and disaster response,” wrote the author of Mapping the Zone

FEMA’s flood maps are used to guide decisions about land use and development, as well as to set building codes. If a flood map is inaccurate, a new building may not have the right support structure to withstand flooding and collapse. Insurance companies use flood maps in pricing their product. Inaccurate flood maps could cause premium rates to not reflect the true risk, leaving homeowners vulnerable. 

Case-in-point: when Hurricane Harvey hit Houston, Texas in 2017, Houston’s flood maps proved to have missed about 75% of the storm's damages. Recovery from Hurricane Harvey cost about $15 billion – a total which could have been less had if flood maps had been updated and accounted for climate change.  

How can we fix the problem of outdated flood maps?

There’s no silver bullet for fixing FEMA’s flood maps, but there are new tools and models that can help. Moored buoy networks and weather buoys are tools that can help update coastal flood maps accurately. 

In the past, flood maps have relied on the measurement of high-water marks left on structures or vegetation to estimate the potential reach of a storm surge. These sources are not always accurate or reliable. Even inland tide gauges are limited in the data they provide: these data sources don’t offer information about the timing of the flooding, the source and sequencing of storm-surge waters, or the magnitude of waves that caused coastal inundation. 

Networks of moored weather buoys can solve some of these issues. Marine buoys  measure waves to both capture the arrival of storms as well as anticipate the impact of waves at the coast: specifically, how will higher sea levels effect waves breaking? Moored buoy networks like Sofar Ocean’s Smart Mooring include a pressure sensor to measure water level and capture storm surges, which temporarily raise sea level high enough to overcome protective barriers such as levies and dunes. The Smart Mooring allows buoys to be anchored offshore, thereby offering a remote warning of incoming sea level rise during stormy events. Moored buoys offer a way to continually take the pulse of the sea state, so communities can detect incoming storms and get ahead of flood risks. Strategies and decisions can then be made according to data patterns or irregularities, rather than guesswork.

With this data at hand, FEMA mapping can account for climate change. It’s vital that flood maps include future projections to accurately depict flood risk. We already know that by some estimates, sea levels are expected to rise by as much as 9.8 feet along the East Coast of the United States by 2100. Just a three feet rise in sea level would impact 4.2 million Americans; a rise of six feet (1.8 meters) could affect 13.1 million. Data from weather buoys can keep a close eye on those projections, as well as help communities plan ahead more effectively. 

To mitigate the floods themselves, many organizations are using buoys to build the second line of defense (after better coastal mapping). DARPA recently launched its Reefense program, designed to develop novel hybrid biological and engineered reef-mimicking structures that can lessen wave and storm damage. By using custom wave-attenuating base structures, DARPA hopes to increase coral or oyster settlement and growth, thereby addressing the infrastructure-related impacts of sea level rise over time. 

Credit: DARPA

Dedicated funding to improve these flood maps is immediately needed. And, luckily, there are groups lobbying on behalf of FEMA to help get government investment “The floodplain association is urging Congress to spend more on flood maps and says it will cost between $3.2 billion and $11.8 billion for FEMA to finish drawing maps for the entire nation. Maintaining and updating the maps will cost $107 million to $480 million a year, the association projected,” reported Scientific American

It’s a massive undertaking to update and rectify the issues with our flood maps. However, the consequences of not making the effort are dire. Tools like moored buoy networks can help measure waves, water temperature water levels, and currents to make the task becomes more manageable. 

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