Quantifying Coastal Flood Risk with Geospatial Data

Coastal flooding occurs when storm surges and high tides inundate normally dry coastal lands. While some level of coastal flooding is a normal part of natural coastal dynamics, particularly in salt marshes and mangrove forests, climate change has resulted in an increased frequency and intensity of these events. This unnatural increase in coastal flooding has placed populations, infrastructure, habitats, and more at risk, leading to billions of dollars in damages worldwide each year.  

This blog explores how Ecopia AI (Ecopia’s) high-precision geospatial data is being used to better understand and analyze coastal flood risk across the US and power climate resilience initiatives. It includes insights and analysis from a recent StoryMap that Ecopia published.

US coastal flooding trends

Coastal flooding events in the US have increased exponentially over the last century as a result of rising sea levels and more frequent high tide flood days. Various elements of climate change have caused this increase, including greenhouse gas emissions that have increased the planet's temperature, melting ice caps and glaciers into seawater. Storm events are also increasing in frequency and intensity, leading to higher levels of wind and precipitation that can impact storm surge and high tide flooding in coastal areas.

Population growth, land use development, urban sprawl, and similar human behaviors also impact coastal flood risk and vulnerability. Almost 40% of the US population lives within 60 miles of the coast  - totaling over 129 million people.

While coastal flood risk differs across the diverse US landscape, many coastal communities are facing similar challenges. For example, as coastal land is developed to support a growing population, impervious surfaces are increasingly replacing more resilient natural land cover that can help absorb flood water. 

Understanding the societal impact of coastal flooding

The US Federal Emergency Management Agency (FEMA) and National Oceanic and Atmospheric Administration (NOAA) define coastal areas as those with a coastline bordering the open ocean or the Great Lakes, or those containing coastal high hazard areas (V-zones). This means that many of the nation's top population centers and their surrounding areas are at risk of the environmental, social, and economic impacts from increased coastal flooding.

Millions of buildings, roads, and other infrastructure exist in these areas, as well as trillions of annual economic activity. In fact, the combined coastal counties of the US have the third largest GDP in the world. 

The coastal US is also extremely densely populated, with about 468 people per square mile compared to the national average of 113. While this entire population is at an increased risk of harm, property damage, and economic implications of coastal flooding, many individuals are disadvantaged, lacking climate resiliency resources. According to NOAA, 22% of the US coastal population exhibit at least 3 components of social vulnerability. These components include income, employment, disabilities, health insurance, vehicle access, age, crowding, caregiver status, and communication accessibility.

Who is most at risk of coastal flooding?

To further quantify this risk and vulnerability in the US, Ecopia mapped out the census tracts of FEMA's National Risk Index identifies as having a total coastal flood risk exposure of greater than 1. Learn more about how risk exposure is calculated here.

We found:

• 41,936,054 people living in areas at risk of coastal flooding
• 275,003 square miles of land at risk of coastal flooding
• Over $7.9 trillion of exposed building value
• Over $19 billion of exposed agriculture value

Next, we symbolized the map to show which census tracts have the highest expected annual loss due to coastal flooding. Expected annual loss takes building and population metrics into account. Explore the interactive map here for a more detailed view of how coastal flood risk and expected annual loss ratings vary across communities in the US.

Next, each census tract was symbolized based on its social vulnerability rating. This rating is calculated using metrics related to income, race, employment, education, health insurance, age, disabilities, access to a vehicle, home types, and English language proficiency. Check out the full StoryMap for a detailed view of social vulnerability ratings in coastal communities across the US.

Community resilience rating was then examined and calculated using 49 indicators representing six types of resilience: social, economic, community capital, institutional capacity, housing/infrastructure, and environmental. Explore the interactive map for a more detailed view of vulnerability ratings in coastal communities across the US.

Next, Ecopia's building footprint data was used to get a clearer picture of the property exposed to coastal flood risk across the country. There are 19,947,701 buildings located within these census tracts. That's over 47.5 billion square feet of property at risk of damage from coastal flooding. Explore the map below to see which buildings are at risk of coastal flooding. Note: basemap imagery is not the same imagery used for feature extraction, so there may be some discrepancies.

How does risk translate across socioeconomic groups?

The analysis was then expanded to include coastal flood risk due to land cover. To see how land cover relates to social vulnerability to coastal flooding, we mapped land cover across the most populous coastal city in each state. We then aggregated that data on a census block group (CBG) level to understand how metrics like the percentage of impervious surface or tree canopy relate to median household income.

To access the full analysis of the coastal cities we examined in each state, click here.

High-precision land cover data for coastal flood risk analysis

This multivariate analysis is made possible by high-precision land cover data derived from geospatial imagery. With classified planimetric-level vector features, it's possible to quantify the amount of each land cover type within a given area. This data can then be used to understand spatial relationships such as in the above socioeconomic analysis, or to power models that predict the impact a coastal flood will have on a community.

A dataset commonly used for this type of land cover analysis is NOAA's publicly available Coastal Change Analysis Program (C-CAP) data. Recent collaboration between NOAA and Ecopia has enhanced the resolution of C-CAP data by 900x, enabling all coastal communities, government stakeholders, and researchers with access to a 1-meter resolution raster dataset to enhance climate resilience analytics and decision-making.

The map slider below compares the amount of detail available between the 1-meter and 30-meter resolution versions of C-CAP data:

While the 1-meter resolution data is freely available to anyone wishing to conduct coastal land cover analysis, Ecopia has also produced vector layers of the same areas for even deeper insights. The vector version of this data is in use by NOAA for internal agency analytics and can be licensed by other organizations as well.

The slider below compares the amount of detail available between the 1-meter raster and vector versions of C-CAP data:

Learn more about Ecopia's work with NOAA here. 

Leveraging AI powered data for climate resilience

While traditional data creation methods like manual digitization are extremely resource-intensive and time-consuming, Ecopia's AI-based mapping systems can digitize entire states in just a matter of weeks - all with the same level of accuracy expected of a trained GIS professional. This efficiency enables NOAA to update C-CAP data more frequently and at higher resolutions than ever before, ensuring land cover data truly represents the real world despite how dynamically it changes.

Many states and communities are already leveraging Ecopia's high-precision land cover data for coastal flooding and climate resilience initiatives. For example, the State of Washington licenses a statewide land cover database from Ecopia to support flood mapping, clean energy, & similar sustainability applications. In just four weeks, Ecopia's AI-powered systems extracted 16 distinct land cover vector layers across Washington's entire 71,429 square mile area, providing state agencies and municipalities with a digital source of truth for the physical world to use in various geospatial analysis workflows and decision-making.

Access high-resolution vector C-CAP data from Ecopia AI

According to NOAA, US coastal areas will experience another 10-12 inches of sea level rise by 2050. That's roughly the same increase that occurred over the last century happening in just under 30 years. Fortunately, geospatial technology is advancing rapidly, providing innovative tools to better predict, mitigate, and respond to coastal flooding events. 

Ecopia AI is on a mission to build a digital twin of the world and solve some of society's most complex challenges. Our AI-based mapping systems enable governments, private organizations, and nonprofits alike to leverage the most comprehensive, accurate, and up-to-date data for geospatial analytics. Get in touch with our team today to access high-resolution land cover data for coastal flood risk and climate resilience analysis.