Global Risks and Research Priorities for Coastal Subsidence

Baton Rouge, La. — Some of the world's largest cities are sinking faster than the oceans are rising. Humans are part of the problem, but we can also be part of the solution through monitoring and modeling.

Coastal lowlands, which rise less than 10 meters above sea level, are particularly vulnerable to the climate change effects forecast for the 21st century, including the threat of inundation by accelerating sea level rise and increases in severity and frequency of tropical storm surges. These threats coincide with a worldwide surge in human population in coastal areas. Coastal population centers include several megacities, whose populations exceed 10 million. Many of these coastal megacities are located on river deltas that are also major centers for agriculture, fisheries, and hydrocarbon production.

To make matters worse, many coastal areas are sinking even faster than the waters are rising: Natural and human-driven subsidence rates arising from shallow processes can be one to two orders of magnitude greater than the rate of climate-driven sea level rise predicted for the remainder of the 21st century (Figure 1).

The risk of rapid coastal subsidence to infrastructure and economies, as well as to the natural environment in coastal lowlands, is global and is most acute in large river deltas, which are home to about 500 million people.

Thus, we have a pressing need to understand what drives coastal subsidence. We must develop better measurements and modeling, and we must link this science with its socioeconomic implications. In response to this need, an international community of researchers organized a series of workshops—one in New Orleans, La. (2013), and another in Venice, Italy (2016).

As a result of this effort, a working group strategy has emerged that uses key geographic sites to design and test measurement and monitoring methods. Here we report our progress on research in the Mississippi Delta in Louisiana, and we summarize recent efforts to expand this research into other coastal areas. However, the larger goal of the coastal subsidence working group is to initiate global research and monitoring initiatives to address the critical knowledge gaps we must fill to protect coastal populations, infrastructure, and natural resources.