New York City has long been known for its iconic skyline, bustling streets, and dense urban landscape. However, scientists are warning that the city faces a growing challenge that goes beyond rising sea levels: the ground beneath it is slowly sinking.

As climate change continues to increase the risk of coastal flooding, New York is becoming more vulnerable than ever. Millions of residents already live in areas at risk of flooding, and projections suggest this number could grow significantly over the coming decades.

To combat flooding, many coastal cities have turned to large-scale engineering projects such as seawalls, flood barriers, elevated roads, and artificial reefs. These structures are designed to keep water out, but they come with major drawbacks. Construction costs can reach tens of billions of dollars, ongoing maintenance is expensive, and these projects often disrupt natural coastal ecosystems. Research has also shown that hardened shorelines typically support fewer species and lower biodiversity than natural coastlines.

Yet rising seas are only part of the problem.

A team of researchers from the U.S. Geological Survey and the University of Rhode Island recently examined another factor contributing to New York City's flood risk: the immense weight of its buildings. Their findings suggest that the city's vast built environment is placing continuous pressure on the ground, contributing to gradual land subsidence.

Subsidence is the process by which the Earth's surface sinks over time. It can occur naturally through geological processes or be accelerated by human activities such as groundwater extraction, mining, erosion, and construction.

For their study, the researchers analyzed nearly 1.1 million buildings spread across New York City's five boroughs. Using publicly available data, they calculated the size and estimated weight of each structure. The analysis considered both the weight of the buildings themselves and the loads created by occupants, furniture, equipment, and other contents.

The results were striking. Collectively, New York City's buildings are estimated to weigh approximately 764 billion kilograms, or around 1.68 trillion pounds. This enormous mass spans roughly 778 square kilometers of urban land.

The challenge is compounded by the city's complex geology. Beneath New York lies a mixture of materials including sand, clay, silt, glacial deposits, bedrock, and areas of artificial fill created during past development projects. Because the underground conditions vary significantly from one neighborhood to another, the impact of building weight is not uniform across the city.

To better understand these variations, the researchers developed regional geological models that account for different soil and bedrock conditions. These models help estimate how much the land may be sinking under the pressure of urban development.

While the sinking occurs gradually—often measured in millimeters per year—even small changes can increase flood risks when combined with rising sea levels and stronger coastal storms. As a result, scientists argue that city planners should consider both climate-driven sea-level rise and land subsidence when preparing New York for the future.

The findings highlight an important reality for many major coastal cities worldwide. Protecting urban areas from flooding will require more than just keeping the water out. Understanding how cities themselves interact with the ground beneath them may become an essential part of long-term resilience planning.