Policy must address the drivers, not just the symptoms, of subsidence

The most productive agricultural region in Southeast Asia and home to 17 million people could be mostly underwater in a lifetime. According to an international team of researchers, saving the Mekong Delta requires urgent and concerted action between countries in the region to reduce the impact of upstream dams and better manage water and sediment in the delta. Their comment, published on May 5 in Sciencedescribes solutions to the region’s dramatic loss of sediments, essential to nourish the lands of the delta.

“It is hard to imagine that a landform the size of the Netherlands and with a comparable population could disappear by the end of the century,” said Matt Kondolf, co-lead author of the study, professor of landscape architecture and environmental planning at the University of California. , Berkeley.

“The Mekong Delta is truly exceptional in terms of agro-economic value and regional importance for food security and livelihoods,” said study co-lead author Rafael Schmitt, a Stanford senior researcher. Natural Capital Project. “Without prompt action, the delta and its livelihoods could become victims of global and regional environmental changes. »

On its journey from the soaring Tibetan peaks to the sea, the Mekong River collects sediment from eroded highlands in China, Myanmar, Laos, Cambodia, Thailand and Vietnam. Nutrient-rich sediments have accumulated in the Mekong Delta and have enabled the lower Mekong region to produce up to 10% of all internationally traded rice. It has also fed fisheries that feed tens of millions of people. Like any river delta, the Mekong Delta can only exist if it receives a constant supply of sediments from its upstream basin, and if water flows can spread these sediments over the lower surface of the delta to build up land to an equal or higher rate. than global sea level rise.

Hungry for renewable energy, countries in the basin have built many hydroelectric dams that block fish migrations, trap sediments and reduce flows downstream. If all the planned dams are built, they will retain 96% of the sediments that once reached the delta. Additionally, the sediment supply of tropical cyclones, which provide about 32% of the suspended sediment load reaching the delta, decreases as cyclone tracks move northward.

Sediment that manages to reach the lower Mekong is mined for sand used in construction and land reclamation. Excessive pumping of groundwater and high levees built to control flooding and enable high-intensity agriculture compound the problem.

To slow and reverse the damage, the researchers recommend that policymakers:

  • Design dams to allow better passage of sediment, place them strategically to reduce their impacts downstream, or replace them with wind and solar farms, if possible.
  • Strictly regulate sediment extraction and reduce the use of Mekong sand through sustainable building materials and recycling.
  • Allow flood waters to spill over the delta and deposit their sediments
  • Limit groundwater pumping in the Mekong Delta
  • Reassessing Intensive Agriculture in the Mekong Delta for Sustainability.
  • Implement natural solutions for large-scale coastal protections along the delta coast

According to the researchers, most delta rehabilitation efforts have involved individual countries addressing isolated engineering challenges and proposing solutions at the local scale. Achieving meaningful progress will require coordination between countries, development agencies, development banks, and other private and civil society actors, the researchers write.

“We are seeing signs that governments and non-governmental actors are starting to work together on these issues,” Schmitt said. “We hope our comment will raise the topic on the regional policy agenda, strengthen conservation in the basin and act as a wake-up call to tackle key drivers of land loss globally. of the system. »

Source of the story:

Materials provided by Stanford Woods Institute for the Environment. Original written by Rob Jordan. Note: Content may be edited for style and length.

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Policy must address the drivers, not just the symptoms, of subsidence

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