Highlights
- Sinking land, or subsidence, is worsening flood risk along Indonesia’s Java Island.
- Land subsidence may account for up to 85% of relative sea level rise by 2050 in some places.
- More than 75% of the island’s coastline is projected to be dominated by subsidence-driven flood risk over the next 25 years.
A study published today in Science Advances finds that land subsidence, or the sinking of the ground, is outpacing ocean-driven sea-level rise along nearly the entire northern coastline of Java Island, Indonesia. The island is home to more than 150 million people—approximately 2% of the global population. The new research offers the most spatially comprehensive assessment of this hazard to date and reveals a problem far larger than the well-publicized sinking of Jakarta.
The study team includes researchers from the Lamont-Doherty Earth Observatory (LDEO)—which is part of the Columbia Climate School, Virginia Tech and the University of California, Irvine, along with international collaborators.
Using satellite radar data and advanced machine learning techniques, the research team mapped land subsidence across Java in unprecedented detail, uncovering widespread and rapidly evolving ground sinking across both urban and rural areas.
Their analysis found that large portions of Java are sinking at rates of up to 1.5 meters per decade, exceeding the rate of global sea-level rise affecting Jakarta, Cirebon, Semarang, Surabaya and other major coastal cities in Indonesia.
“This study reveals a fundamental shift in how we understand coastal risk,” said lead author Leonard Ohenhen. “In many parts of Java, the land itself is sinking so rapidly that it is overwhelming the effects of ocean-driven sea-level rise. That means the hazard is not just coming from the ocean; it is being driven from below the ground.”
Ohenhen, who is now an assistant professor at UC Irvine, conducted the work while he was a postdoctoral fellow at LDEO.
By integrating satellite observations with sea level projections, the researchers found that land subsidence could account for up to 85% of relative sea-level rise along much of Java’s coastline by 2050, and that more than 75% of the coastline is projected to be dominated by subsidence-driven flooding risk over the next 25 years. Coastal communities are already experiencing relative sea-level rise rates far exceeding global averages.
While global climate change is raising sea level, the study highlights that local human activities, especially groundwater extraction, are causing local land subsidence and amplifying flood risk.
The team identified key drivers of subsidence, including intensive groundwater withdrawal in urban areas, agricultural water use, industrial extraction and natural sediment compaction in delta regions.
“One of the most important findings of this study is that we were able to identify the key factors driving land subsidence, and how much they contribute to relative sea level rise in a densely populated region facing multiple hazards,” said co-author Folarin Kolawole, a structural geologist at LDEO and an assistant professor in Columbia’s Department of Earth and Environmental Sciences. “This kind of high-resolution assessment is needed in coastal regions around the world.”
“What matters most for coastal communities is not just global sea level, but how the land and sea are changing in that specific place.”
James Davis, Lamont-Doherty Earth Observatory
To overcome the lack of ground-based monitoring in many regions, the researchers developed a novel approach using satellite data to create “virtual tide gauges” every five kilometers along the coastline.
This allowed them to reconstruct past and future sea level changes with unprecedented spatial detail, revealing highly variable and rapidly changing risk patterns.
“This study shows how crucial it is to measure vertical land motion near the coast and include it in any serious assessment of sea-level risk,” said co-author James Davis, a geodesist at LDEO. “What matters most for coastal communities is not just global sea level, but how the land and sea are changing in that specific place.”
Although focused on Java, the findings have global implications.
“Many coastal regions around the world are facing similar, but often unseen, dynamics,” Ohenhen said. “What we see in Java is likely a preview of what could unfold elsewhere if subsidence is not properly monitored and managed.”
The researchers emphasize that effective climate adaptation must go beyond managing ocean rise to include active monitoring and mitigation of land subsidence.
“Subsidence is one of the most actionable components of coastal risk,” said Virginia Tech geoscientist Manoochehr Shirzaei, a co-author of the study. “Unlike global sea level rise, which requires global solutions, subsidence can often be managed locally through policy, infrastructure and sustainable resource use.”
The findings underscore the importance of tracking sinking land alongside the rising sea surface in vulnerable coastal regions.
Adapted from a press release written by Kelly Izlar for by Virginia Tech.
