Satellite radar maps reveal rapid delta land loss

by Erica Marchand
Paris, France (SPX) Feb 18, 2026

Earths river deltas, home to about 5 percent of the global population and some of the worlds major cities, are sinking as land subsides faster than the sea is rising in many locations. New satellite radar observations from the Copernicus Sentinel 1 mission reveal that subsidence is a major and often dominant driver of relative sea level rise in these low lying regions.

Ten of the worlds 34 biggest cities are built on river deltas, making these environments critical hubs for people, infrastructure, trade and ecosystems. Major metropolitan areas such as Kolkata in the Ganges delta, Alexandria on the Nile, Shanghai on the Yangtze, Bangkok on the Chao Phraya, Ho Chi Minh City on the Mekong and New Orleans on the Mississippi stand just a few meters above sea level, leaving them exposed to any loss of land elevation.

A new global analysis, published on 14 January in the journal Nature, used a decade of Copernicus Sentinel 1 radar data to map surface elevation changes across 40 large river deltas worldwide. The study shows that more than half of these deltas are subsiding at rates faster than 3 millimeters per year, highlighting that sinking land is already matching or outpacing present day geocentric sea level rise in many regions.

The research team focused on deltas with populations above 3 million people, as well as historically recognized sinking deltas and several less studied systems. Deltas typically sit only one or two meters above sea level, and their elevation can evolve through natural processes such as sediment deposition, erosion and compaction, along with vertical land motion driven by movements of the Earths crust.

In deltas such as the Chao Phraya in Thailand, the Mekong in Vietnam and the Yellow River in China, the analysis indicates that land subsidence now dominates relative sea level rise. As the ground surface sinks, these regions become more vulnerable to coastal flooding, permanent land loss, saltwater intrusion into freshwater systems and more damaging storm surges during extreme weather events.

The study identifies human activity as a key accelerator of elevation loss in many of the 40 deltas examined. Excessive groundwater pumping lowers pore pressures and causes sediments to compact. Oil and gas extraction can also induce subsidence. Rapid urbanization and the expansion of agriculture reshape land surfaces, while dams and other upstream modifications alter sediment delivery, reducing the material available to naturally build up deltas.

Deltas with faster growing urban populations tend to show higher subsidence rates, underlining the link between development pressures and ground sinking. The Yellow River, Po, Nile, Chao Phraya and Mekong deltas all feature in the analysis as examples where intensive human use coincides with pronounced vertical land motion. Coastal cities including Alexandria, Bangkok, Dhaka, Kolkata, Shanghai, Yangon, Can Tha, Thai Binh, Niigata, Jakarta, Surabaya and Dongying are reported to experience above average subsidence.

Although river deltas cover less than 1 percent of Earths land surface, they host up to 500 million people. The authors report that of the 76 million people living in delta areas with elevations below 1 meter, roughly 84 percent, or about 63.7 million people, inhabit rapidly sinking parts of these landscapes. This concentration of population in the lowest and fastest subsiding zones sharply increases risk to homes, livelihoods and infrastructure.

While Asian deltas face particularly high exposure to subsidence, the study encompasses systems on all inhabited continents. In the Americas, the Amazon and Mississippi deltas are among seven deltas that together account for more than 57 percent of the total subsidence detected. The remaining five high contribution deltas are the Nile in Africa and the Ganges Brahmaputra, Mekong, Yangtze and Irrawaddy deltas in Asia.

Lead author Leonard Ohenhen, Assistant Professor at the Department of Earth System Science, University of California, Irvine, said that the team compared subsidence to both current and projected sea level rise. Our analysis shows that current average subsidence rates exceed geocentric sea level rise in 18 of the 40 deltas studied, and in a few deltas even projected sea level rise at the end of the century. These results call for targeted interventions to address subsidence, in parallel with broader efforts to mitigate and adapt to climate change driven global sea level rise.

To quantify land motion, the researchers used high resolution interferometric synthetic aperture radar, or InSAR, products generated from the full Copernicus Sentinel 1 archive between 2014 and 2023. Sentinel 1 satellites carry C band SAR instruments that repeatedly image Earths surface, allowing precise tracking of ground level changes over time through interferometric analysis of phase differences between radar passes.

By applying advanced multitemporal InSAR techniques, the team derived detailed maps of surface elevation change and vertical land motion for each delta. The long, continuous dataset provides a consistent global view of how deltas are deforming, making it possible to separate local subsidence patterns from broader signals of sea level rise and other geophysical processes.

Nuno Miranda, Sentinel 1 Mission Manager at the European Space Agency, said the findings highlight the missions role in climate and hazard science. This study demonstrates Sentinel 1s unique capacity to provide uninterrupted, high resolution, global InSAR measurements. It confirms the Sentinel 1 mission as an essential pillar of global climate and hazard science, proving that systematic SAR observations are key for quantifying subsidence drivers and guiding sustainable adaptation strategies at global scale.

With river deltas hosting hundreds of millions of people and accommodating major agricultural zones, ports and industrial complexes, understanding subsidence is crucial for planning future defenses and land use. The new global assessment underscores that managing delta risk will require addressing human driven land sinking alongside climate driven sea level rise, so that governments and communities can design effective strategies to protect some of the planets most vulnerable and economically important coastal regions in the decades ahead.

Research Report:Global subsidence of river deltas