In Vietnam’s Mekong Delta, home to about 17 million people, large areas of land have been poldered for the cultivation of crops such as rice and shrimp. The delta is currently less than one meter above the sea level. But due to accelerated land subsidence, mainly caused by groundwater extraction, a shortage of river sediment, and rising sea levels, researchers from Wageningen University & Research and Utrecht University predict that by 2050 large parts of the delta will have fallen below sea level if nothing changes soon. What can Vietnam do to keep above water?
Relative sea-level rise
Using new computer models, the researchers looked at how the delta will develop over the next 30 years, taking into account predictions for land subsidence, sea-level rise and sediment shortages. “We saw that the delta will likely sink very fast compared to sea level,” says Frances Dunn, researcher at Utrecht University and one of the two authors of the new study, which was published in Nature Communications Earth and Environment earlier this week.
” Although the delta sinks naturally, in recent years, land subsidence has been dramatically accelerated by humans because of unsustainable groundwater extraction,” says Philip Minderhoud assistant professor at Wageningen University & Research, second author of this study. “This combination land subsidence and sea level rise is what we refer to as’relative ocean-level rise’, and it is what delta residents experience.”
Dunn adds, “For the future of the people who live and earn their living there, these high rates of relative sea-level rise are worrying. “
Local sediment strategy
One strategy to mitigate land subsidence and increase the delta is to accumulate sediment in certain areas of the delta. Dunn illustrates, “For instance, we looked at the impact of sedimentation around Can Tho.” Even then, there’s only one way to protect the city from sedimentation. The river is on the other side, while the rest of delta sinks because it doesn’t receive river sediment. “
Local segregation is not the panacea for Vietnam. Minderhoud says that there is not enough sediment to make up for the rapid sinking of the delta relative to sea level. However, the researchers say that such a sedimentation strategy could be combined with measures to prevent human-induced land subsidence and strategies to retain organic material coming from–for example–rice agriculture, as opposed to fluvial sediment which is carried in by the river. In this way, Vietnam can considerably del