The Delta Is Sinking

The Cái Răng floating market starts at five in the morning and is a wholesale operation, not a performance. Boats hang a sample of what they carry from a bamboo pole — a pineapple, a bunch of radishes, a cabbage — so that a buyer can read the market from two hundred metres away. It has worked this way for a century and it is getting smaller every year, because the roads got better and because the delta that feeds it is going under.

The Vietnamese Mekong Delta produces more than half the country's rice and around 70% of its fruit and aquaculture, on about 40,000 square kilometres of alluvium sitting on average less than a metre above sea level. Something in the region of 17 million people live on it. It is sinking at a rate of roughly one to four centimetres a year, in places faster, and the sea is rising to meet it.

Three problems, only one of which is the climate

The subsidence is the first and it is largely self-inflicted. Groundwater extraction across the delta — for drinking, for aquaculture, for industry — has accelerated since the 1990s, and pumping water out of the aquifer compacts the sediment above it. Studies published over the last decade have put average subsidence well above the rate of sea level rise. The delta is going down faster than the ocean is coming up.

The second is sediment. A delta is not a static thing; it is the balance between what a river deposits and what the sea removes. The Mekong historically carried around 160 million tonnes of sediment a year to the coast. Hydropower dams upstream — dozens now operating in China, Laos and elsewhere in the basin — trap a large and growing share of it behind their walls. Estimates of the reduction vary and are contested, but the direction is not in dispute: less sediment arrives, and the delta stops building.

The third is sand. Sand mining from the riverbed, much of it feeding the construction booms in Ho Chi Minh City, Phnom Penh and Singapore, removes material directly. It deepens the channel, undercuts the banks and accelerates saline intrusion up the river. Bank collapses that take houses into the water are now routine enough in the delta that local news reports them the way other places report traffic accidents.

The delta is going down faster than the ocean is coming up, and the largest single cause is the water being pumped out from underneath it.

Salt

The consequence that farmers talk about is salinity. When the river runs low and the land sits low, seawater pushes up the channels — in the 2016 and 2020 dry seasons it reached more than 90 kilometres inland in places, into provinces that had never seen it. Rice does not tolerate salt. Fruit orchards, which take years to establish, tolerate it less.

The adaptation has been substantial and largely bottom-up. Farmers in the coastal provinces have shifted from three rice crops a year to two, or to one rice crop and one of shrimp, using the saline season rather than fighting it. Rice-shrimp rotation is now practised across hundreds of thousands of hectares and is, on most measures, more profitable than triple rice. Government policy caught up in 2017 with Resolution 120, which explicitly reoriented delta planning from "control the water" to "live with it" — an unusually clear-eyed piece of national policy.

What that policy cannot do is put sediment back in the river or unbuild the dams. Those decisions are made in Beijing, Vientiane and the boardrooms of regional power utilities, and the Mekong River Commission, which coordinates the lower basin states, has consultative powers rather than a veto.

What a visitor sees

Not very much, which is part of the problem. Take a sampan through the channels around Bến Tre or Vĩnh Long and you see coconut groves, brick kilns, fish farms under the houses and a landscape that looks abundant, because it is. The delta is not visibly dying. It is losing a few centimetres a year and a few kilometres of coastline a decade, which is invisible over a three-day trip and catastrophic over fifty years.

What you can see, if you ask, is the response. Sea dykes and sluice gates along the coastal provinces. Mangrove replanting, which is the cheapest effective coastal defence anyone has found and which is being undone in places by shrimp ponds. Houses raised on new plinths. And in Cần Thơ and the larger towns, a visible migration effect — the delta has been losing people to Ho Chi Minh City for a decade, and out-migration from the coastal provinces is among the highest in the country.

Going anyway

The delta is worth several days and most itineraries give it one, usually a day trip from Ho Chi Minh City that visits a coconut candy workshop and returns. Stay instead — Cần Thơ for the market at dawn, a homestay in Bến Tre or Vĩnh Long, and if there is time, Châu Đốc in the west where the Cham Muslim community lives along the Bassac and Sam Mountain rises out of the floodplain.

Go by boat as much as possible, since the road network has quietly replaced the water one over twenty years and the channels are where the delta still makes sense. And ask about salt. Every farmer in the coastal provinces has a view on it, most of them have changed what they grow because of it, and it is a more interesting conversation than the one about coconut candy.