Global analysis: subsidence in deltas often faster than sea level rise
Expert(s) |
Philip Minderhoud
River deltas are among the most densely populated and economically vital areas worldwide but they are exposed to increasing risks from relative sea level rise. New high-resolution satellite analyses (InSAR with Sentinel-1, 2014-2023) show that land subsidence in forty deltas on five continents is widespread and, in many cases, faster than sea level rise. The study provides consistent, delta-wide measurements at 75 m resolution and it has now been published in Nature.
Subsidence increases the threat to vulnerable deltas worldwide
“We already knew that rising sea levels are a threat to these valuable delta areas but the fact that they are subsiding in so many places around the world is intensifying the effect and therefore exacerbating the risks of flooding, land loss and salinisation,” says Philip Minderhoud, a researcher at Deltares and Wageningen University and Research Centre, and co-author of the article 'Global subsidence of river deltas'.
“For many deltas, there is a major shortage of ground-based observations of elevation and subsidence. That makes it difficult to quantify the overall vulnerability of these deltas accurately. It is relatively expensive and time-consuming to establish a clear picture of subsidence in an entire delta with direct measurements – let alone forty major delta systems worldwide – even though that is necessary as a basis for effective action.”
New satellite insights expose widespread elevation loss in vulnerable deltas
At present, most observations of land subsidence have been limited to the main urban centres in deltas. As a result, our understanding of the situation in rural and ecological areas, which are very important for things like global food production, continues to be less than optimal in many deltas.
In the paper, the researchers present estimates of land subsidence in forty deltas worldwide using monitoring data – InSAR observations – based on radar images from the Sentinel satellite. They used those datasets to quantify elevation loss and demonstrate the severity of land subsidence in these low-lying vulnerable deltas around the world.
More than 50% of deltas are subsiding by more than 3 mm annually
More than half of the deltas have subsidence rates exceeding 3 mm per year. In thirteen of these deltas – the Nile, Po, Vistula, Ceyhan, Brahmani, Mahanadi, Chao Phraya, Mekong, Red River, Ciliwung, Brantas, Godavari and Yellow River – average land subsidence exceeds the current estimates of global sea level rise, in other words about 4 mm per year. Average land subsidence in the deltas of the Chao Phraya (Thailand), Brantas (Indonesia) and Yellow River (China) is more than twice current global sea level rise.
Groundwater extraction main factor in subsidence
In ten of the forty deltas, groundwater extraction is the main factor driving subsidence. Anthropogenic interventions have accelerated land subsidence in many of the world’s major deltas. They include excessive groundwater extraction, oil and gas extraction, and changes in land use associated with urbanisation, agriculture and aquaculture.
Deltas where large amounts of groundwater are extracted and where population growth is higher tend to have higher rates of subsidence. Examples include the deltas of the Yellow River, the Po River, the Nile River, the Chao Phraya River and the Mekong River.
Deltas are subsiding faster than sea rise
The new observations show that, for most deltas in the twenty-first century, the current rate of subsidence is exceeding global sea level rise due to global warming as the main cause of relative sea level rise. Targeted measures are needed to address subsidence, alongside broader action to mitigate global sea level rise caused by climate change and adapt accordingly.
“Our findings are very worrying and they require a proactive approach to the problem,” says Minderhoud. The good news is that government authorities can institute measures locally to mitigate rapid land subsidence caused by human activity.
For example, limiting the amount of groundwater extraction has significantly reduced land subsidence in delta cities such as Shanghai, Bangkok and Ho Chi Minh City. This also opens up effective options for the wider, surrounding delta areas to tackle relative sea level rise at the local level without waiting for a global consensus.
Graphs taken from: Ohenhen, L.O., Shirzaei, M., Davis, J.L. et al. Global subsidence of river deltas. Nature (2026).
