A new study published in Science Advances reveals that sinking land — not just rising oceans alone — will be the main cause of future coastal flooding along Indonesia's densely populated Java Island, putting millions at risk sooner than expected.
"We often frame sea-level rise hazards as a climate-driven process, but in many of the world's most vulnerable regions, human-induced sinking land is the dominant driver," said Manoochehr Shirzaei, Virginia Tech geoscientist and co-author of the study. "If we ignore that, we are fundamentally underestimating risk."
Using satellite radar data and advanced machine learning techniques, the research team mapped land sinking, or subsidence, across Java at unprecedented detail. The analysis uncovered subsidence rates of 1 to 15 centimeters per year across both urban and rural areas, far exceeding global sea level rise.
Key findings point to groundwater withdrawal in urban areas, agricultural water use, industrial extraction, and natural sediment compaction in delta regions as the major culprits.
By integrating satellite observations with sea level projections, the researchers demonstrated that:
- Land subsidence will account for up to 85 percent of relative sea level rise along much of Java's coastline by 2050.
- More than 75 percent of the coastline will be dominated by subsidence-driven flooding risk over the next 25 years.
To overcome the lack of ground-based monitoring in many regions, the researchers developed an approach that uses satellite data to create virtual tide gauges every 5 kilometers along the coastline.
While global climate change is raising ocean levels, the study highlights that human activities on the local level — especially groundwater extraction — are accelerating land subsidence, amplifying flood risk.
Although focused on Java, the findings have global implications.
"Many coastal regions around the world are facing similar, but often unseen, dynamics," said lead author Leonard Ohenhen, a former Virginia Tech graduate student now at the University of California, Irvine. "What we see in Java is likely a preview of what could unfold elsewhere if subsidence is not properly monitored and managed."
The researchers emphasized 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," Shirzaei said. "Unlike global sea level rise, which requires global solutions, subsidence can often be managed locally through policy, infrastructure, and sustainable resource use. That makes it a critical lever for building resilience."
Orginal study : DOI 10.1126/sciadv.aec0172
