The Mekong Delta in Vietnam could be nearly fully submerged by the end of the century if urgent actions are not taken across the river basin. Continuing with business as usual could drown 90% of this agro-economic powerhouse that’s home to nearly 20 million people – with immense local and global impacts.

Only concerted action by the six countries in the Mekong basin and better management of water and sediments within the delta could avoid such a devastating outcome, argues an interdisciplinary research team in the commentary Save the Mekong Delta from drowning, recently published in Science.

Most of the 40,000 km2 delta is less than 2m above sea level and is thus prone to climate change induced sea level rise. On top of that, actions in the delta such as over-pumping of groundwater and unsustainable sand mining to construct expanding cities across Asia as well as rapid hydropower development upstream threaten the future of the most productive rice basket in Southeast Asia.

“It's hard to fathom that a landform the size of the Netherlands and with a comparable population might disappear by the end of the century,” said lead author Professor Matt Kondolf from the University of California, Berkeley. “Yet, like any river delta, the Mekong Delta can only exist if it receives a sufficient sediment supply from its upstream basin and water flows to spread that sediment across the delta surface, so that land is built at a rate that is equal to or greater than global sea level rise.”

"Over the last few years we have thoroughly studied the impact that the Mekong Delta is undergoing due to economic development and social changes that have occurred especially in recent decades", explained Dr. Simone Bizzi who collaborated with other research on the Mekong Delta, together with the main authors of this study, also winning the Aspen Institute Italia Award 2021.

In the Mekong, water and sediment flows are increasingly endangered.

“Hungry for renewable energy, countries in the basin develop hydropower dams, which trap sediment, with little regard for system scale impacts. What little sediment reaches the lower Mekong could be mined to meet the demands of the burgeoning real estate sector in the region, which requires great amounts of sand for construction and land reclamation,” summarised co-lead author Dr. Rafael Schmitt from the University of Stanford and Dr. Simone Bizzi from Department of Geosciences of the University of Padova.

But not all the blame can be put on upstream actions and global climate change induced sea level rise. In the delta itself, high dikes have been built to control floods and thus enable high-intensity agriculture. This also prevents the fertile sediment from being deposited on the rice fields.

On top of that the delta itself is sinking due to land subsidence. “Land subsidence in a delta is a natural process, but in recent decades the delta has been sinking faster and faster due to increasing human activities, such as excessive groundwater extraction. Large parts are subsiding 10-20 times faster than sea level is rising,” according to Dr. Philip Minderhoud, co-author of the article, Marie-Curie research fellow at the Department of Civil, architectural and Environmental Engineering, University of Padova, and Assistant Professor at Wageningen University, The Netherlands. “In addition, we have recently discovered that the delta is a lot lower elevated above sea level than previously thought, less than a meter on average. This combination means that the area is extremely vulnerable and if the current development continues, large parts could sink below sea level as early as in the next ten to twenty years.”

However, the drowning of the delta is not a fait accompli. There are steps that can be taken to allow dynamic, natural processes to help prevent the delta from further sinking and shrinking.

The team identified six measures that are feasible and have global precedents and would significantly increase the lifetime of the delta:

- Avoid high impact hydropower dams by replacing planned projects with wind and solar farms when possible and if not, building new dams in a strategic way that reduces their downstream impacts;

- Design and/or retrofit hydropower dams to enable better sediment passage;

- Phase out riverbed sand mining and strictly regulate all sediment mining, while reducing the need for Mekong sand through sustainable building materials and recycling;

- Re-evaluate intensive agriculture in the Mekong Delta for its sustainability and reduce depletion of groundwater reserves by overexploitation;

- Maintain connectivity of delta floodplain by adapting water infrastructure; and

- Investing in natural solutions for coastal protections on a large scale along the delta’s coasts.

“This is an emblematic case study as the type of challenges we must face in the Mekong Delta are in many ways comparable to those threatening other regions of the world. Our capacity to address politically, economically, and scientifically them will assess our ability to sustain in the near future a healthy and livable planet” underlined Dr. Simone Bizzi.

“A Mekong delta that will thrive beyond the end of this century is possible – but it will require fast and concerted action in a basin that has been riddled by competition, rather than cooperation, between its riparian countries,” concluded Professor Kondolf.