The great salt drought desiccating Vietnam’s Mekong Delta

“Well I can tell you, all my fish are dead now.”

Nguyen Thi Bach Vien sounds more resigned than anything else. She is calling from her home in Ben Tre province, a few hours drive south of Ho Chi Minh City in the belly of Vietnam’s Mekong Delta, where she has a fish farm and gardens of coconut and pomelo trees.

Vien’s freshwater shrimps and giant river prawns are dying, too.

The 62-year-old has spent her whole life on her land, watching the soil gradually change and the air grow more sweltering every year. Now she fears that she and her husband are likely to be the last of their family to work solely on the farm.

“Dead fish and dead shrimps,” Vien says, “and if we don’t have a solution soon, I think, dead farmers too.”

The issue is water. Salty seawater has intruded into the freshwater Mekong Delta at unprecedented levels this year, to the point at which peoples’ crops and produce simply cannot survive.
The Mekong Delta is a vast spread of fertile riverbeds, islets and mangrove swamps at the end of the Mekong River, where Vietnam’s coastline meets the sea. It spans about 65,000sq km (25,100sq miles) and is home to more than 20 percent of Vietnam’s population.

The Mekong River feeds into it from as far north as Qinghai, China, winding down through Tibet and Southeast Asia, providing what has historically been an Eden for natural life.

There are millions of farmers like Vien across the delta suffering huge losses, but there is little they can do except hope things change before there is nothing left.
A broken system

Seawater flows into the Mekong River every year as part of the natural delta system, but it has never intruded so far or with such intensity.

Normally, the Mekong turns salty only for a month or so but, this year, farmers have had to endure at least four months of salinity and the situation seems set to continue.

Salty seawater began to enter the delta early in mid-November 2019 and by January this year, seawater was projected to reach 30-40km deeper than the annual average during the full dry season. Fast forward to mid-April, and the high salinity levels are expected to remain into May unless the monsoon season can help reset the balance.

Higher salinity levels are due to several factors, including a lack of fresh water washing downstream into the delta, and a deepening riverbed. This has been, to some extent, compounded by the effects of climate change.
When the Mekong system is functioning normally, it floods every wet season. Fresh water from upstream surges through the delta and into the sea.

Cambodia’s Tonle Sap Lake, reportedly responsible for 30-35 percent of the delta’s water supply, is filled by these floods and then, in the dry season, it slowly discharges water into the delta. This allows fresh water to continue to wash seawater out despite there being no rain.

The lake would usually be fully drained by around March, which would result in higher salinity, but only for a month or so until the monsoon came and the Mekong Basin began flooding once again.

One month is manageable for farmers who would simply save water for the salt season.

“People would always have barrels of water ready. My farm has five ponds with which we collect rainwater throughout the year,” Vien says.

But this year, Tonle Sap did not fill up and the salt has sat in the delta for months on end.

The main culprits are upstream dams, which control water and sediment levels during the monsoonal floods, and sand mining, which is depleting the riverbeds.
The upstream dams

There are six existing dams in China, one in Laos in the Lower Mekong Basin, and at least 300 on tributary waterways. The dams use floodgates to release the wet season floods in a more controlled manner.

“[The] water eventually leaves the dams, but with a little bit of a slower pace,” says Sepehr Eslami, a coastal engineer, senior researcher and adviser for Utrecht University and Deltares in the Netherlands.

This prevents Tonle Sap from filling during the monsoon because the peak discharge is no longer there. This means there is then less to run into the Mekong Delta which, according to Sepehr, is lacking 10 billion cubic metres (2.64 trillion gallons) of water during the dry season.

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