Beijing (VNA) – Vietnam should invest in public awareness, train local scientists and strengthen coordination between local and central authorities to address the growing risks of sea-level rise and land subsidence, according to Professor Yucheng Lin, an Assistant Professor at City University of Hong Kong (CityUHK), China.
In an interview with the Vietnam News Agency’s correspondents in Hong Kong (China), Lin, an expert specialising in sea-level change and climate risk assessment, said Vietnam shared global drivers of sea-level rise with China’s coastal regions, but local conditions could lead to significant differences in the overall risks.
The two main global drivers are melting polar ice sheets and the expansion of seawater as the oceans warm. Paradoxically, Vietnam and southern China could experience sea-level rise up to 20% above the global average because of their distance from the polar ice sheets. As the ice sheets shrink, their gravitational pull weakens, allowing water to move towards distant coastlines. Changes in ocean currents also push additional water onto the shallow continental shelves of the South China Sea.
As a result, Hong Kong and Ho Chi Minh City could experience similar sea-level rise driven by ocean processes, Lin said.
However, land subsidence poses an additional and serious threat to Vietnam. Major Vietnamese cities are located on river deltas, where soft sediments, excessive groundwater extraction and the weight of heavy construction contribute to sinking land.
A satellite survey of 48 major coastal cities worldwide found that Ho Chi Minh City had the fastest subsidence rate, with some areas sinking by nearly 4cm a year. Some parts of Hanoi have recorded subsidence of up to 5cm annually, while the Mekong Delta is sinking by 1–3cm a year. The delta has an average elevation of less than one metre above sea level.
These rates are significantly higher than the current global sea-level rise of around 5mm a year, highlighting the importance of effective land-use planning and groundwater management.
Lin recommended that Vietnam prioritise investment in people, particularly by raising public awareness and developing a domestic team of scientists capable of assessing sea-level risks and designing appropriate responses.
He warned that sea-level rise could threaten homes and communities within people's lifetimes. Higher sea levels allow storm surges to travel further inland, making coastal floods that once occurred once a century potentially recur every decade or even every year. Saltwater intrusion also threatens rivers and farmland.
The severe saltwater intrusion in the Mekong Delta in 2016, which damaged rice-growing areas in a region supplying about 90% of Vietnam’s rice exports, demonstrated the potential economic and social costs, he said.
Vietnam also needs specialists who understand ocean dynamics, movements of the Earth's crust and changes in polar ice sheets.
Their expertise would help translate global projections into plans suited to the geographical and socioeconomic conditions of individual localities, while identifying cost-effective measures.
Lin stressed that sea-level rise is a complicated problem that cuts across many sectors and stakeholders, but uncertainty involved in future sea-level projections is no reason to wait.
Policymakers should first recognise that their own decisions can change the outlook quickly. Shanghai was once a fast-sinking city: parts of it dropped by more than a metre during the 20th century as groundwater was pumped out. The city then strictly limited pumping and injected water back into its aquifers. Its sinking greatly slowed already, and some ground even rose back slightly.
Bringing this threat under control has supported Shanghai’s sustainable development and given investors confidence in its future.
Second, critical infrastructure, such as power plants, ports and water supply, needs special attention. Sea-level science keeps evolving as we learn more about ice sheets and ocean dynamics, so projections should be updated regularly. Decisions about long-lived infrastructure, however, cannot wait for the science to settle. Where failure would be catastrophic, as with the nuclear power plant Vietnam plans to build on its south-central coast, designs should allow for the high end of the range. One benchmark is the IPCC’s low-likelihood, high-impact scenario, in which global sea level could approach 2 metres by 2100.
Finally, coastal engineering is expensive, and Vietnam’s coastal provinces differ in both their risks and their resources. Local governments need to work with regional and national governments to find the most suitable and cost-effective plan for each place./.
