Article image

Sinking ground amplifies flood risk from sea level rise

A recent study led by Virginia Tech has found that sections of the Chesapeake Bay are sinking at a rate of nearly seven millimeters per year. Unfortunately, up-to-date knowledge of where the ground is sinking and by how much is currently not included in the official planning maps which authorities use to assess the flooding risk from rising sea levels. 

This phenomenon poses a significant challenge to present and future management efforts, which are likely to either underestimate or overestimate flooding risk to coastal communities from the Virginia shoreline.

The scientists used interferometric imaging with synthetic aperture radar from the Earth’s orbit to measure how much the land along the Chesapeake Bay’s shoreline had sunk between 2007 and 2020. By using this data, they estimated potential flooding through the 21st century caused by land elevation changes, sea level rise, and storm surges.

“Although we found that most of the bay is sinking by less than 2 millimeters a year, in several areas we discovered subsidence rates of 4 to 5 millimeters per year and more,” said study lead author Sonam Futi Sherpa, a doctoral student in Geosciences at Virginia Tech. 

Some hotspots of land subsidence occurring at a relatively higher rate and further exacerbating the effects of sea level rise and storm surges include Norfolk, Newport News, and Virginia Beach (parts of Chesapeake Bay’s Hampton Roads). While many of these hotspots are sites of intense anthropogenic activity, such as groundwater pumping causing the compaction of aquifer systems, some of them are areas where land is lost due to erosion.

When examining various sea-level rise scenarios compounded with the effects of land subsidence, the scientists found that, by the end of the century, between 454 and 600 square kilometers will face a significant risk of flooding. In addition, massive storm surges such as 2003’s Hurricane Isabel could increase the flooded area from 849 to 1,117 square kilometers under a very high greenhouse emissions scenario.

“There are many estimates and models for sea-level rise, but they all fall short because they don’t take into account land elevation changes,” said co-author Manoochcher Shirzaei, an associate professor of Radar Remote Sensing Engineering and Environmental Security at Virginia Tech. 

“When formerly dry land becomes flooded, it causes saltwater contamination of surface and underground water, and it accelerates coastal erosion and wetland losses. The flooding hazards maps of the Chesapeake Bay area need to be updated with the measurements of land elevation changes and updated projections of sea level rise.”

According to the researchers, sinking ground along the shoreline significantly magnifies the effects of sea level rise: as the ground goes down and the sea level comes up, flood waters will go much further inland. However, since various locations face different rates of land subsidence, long-term solutions to mitigate emergent problems should be tailored to each individual situation.

“Adaptation to relative sea level rises comprises three main categories of defense: protection, accommodation, and retreat. And coastal communities can choose and pick from a long list of options, such as upgrading protection facilities (e.g. dams), raising lands, maintaining and restoring wetlands protection, controlling subsidence, improving flood resiliency, selective relocation of important infrastructure, and installing flood warning systems,” Shirzaei concluded.

More about sea level rise

Sea level rise refers to the increase in the average global sea level, primarily driven by the melting of ice sheets and glaciers, as well as the expansion of seawater due to rising temperatures. This phenomenon is a significant consequence of climate change and poses substantial challenges to both human societies and the environment.

Impacts on humanity

Coastal flooding

As sea levels rise, the frequency and intensity of coastal flooding events increase, threatening the lives and properties of millions of people living in low-lying coastal areas.

Erosion and loss of land

Shorelines recede due to increased erosion, leading to the loss of valuable land, including agricultural fields, residential areas, and infrastructure.

Displacement of populations

Rising sea levels can lead to the permanent inundation of coastal areas, forcing millions of people to relocate. Climate refugees may face social, economic, and political challenges as they seek new homes.

Damage to infrastructure

Critical infrastructure, such as roads, bridges, and power plants, can be damaged or destroyed by rising sea levels and the resulting increased flooding.

Economic impact

The loss of land, displacement of populations, and damage to infrastructure can significantly impact regional and global economies, disrupting trade, tourism, and other economic activities.

Impacts on the environment

Loss of coastal ecosystems

Rising sea levels can lead to the loss of critical coastal habitats such as wetlands, mangroves, and salt marshes. These ecosystems serve important ecological functions, including providing habitat for numerous species, filtering pollutants, and acting as natural buffers against storms and flooding.

Saltwater intrusion

As sea levels rise, saltwater can infiltrate freshwater aquifers and estuaries, affecting the quality and availability of drinking water and harming freshwater ecosystems.

Changes in ocean chemistry

Rising sea levels can lead to changes in the distribution and concentration of nutrients and pollutants in the ocean, which can impact marine life and ecosystems.

Altered species distribution

Sea level rise can affect the distribution of marine species by altering their habitats, potentially leading to shifts in the composition and structure of ecosystems.

Impacts on coral reefs

Coral reefs, which are essential for the survival of many marine species, can be negatively affected by sea level rise, as increased water depth can reduce the amount of sunlight reaching the reefs, hindering the growth of the coral-building algae.

Mitigation and adaptation strategies are essential to minimize the impacts of sea level rise on humanity and the environment. These can include reducing greenhouse gas emissions, investing in renewable energy, improving coastal infrastructure, implementing managed retreat strategies, and restoring and preserving critical coastal ecosystems.

The study is published in the Journal of Geophysical Research: Solid Earth.

By Andrei Ionescu, Staff Writer

Check us out on EarthSnap, a free app brought to you by Eric Ralls and

News coming your way
The biggest news about our planet delivered to you each day