Under siege by climate, man-made problems, a sinking Ho Chi Minh City fights to survive
The city is facing extreme weather more frequently, its flood mitigation responses have not kept pace, and a proposed sea dyke has sparked debate. The programme Insight finds out why the solutions will not be easy.
HO CHI MINH CITY: Nguyen Van Cu is a construction engineer whose speciality is raising homes. That means he has been busy of late.
He recently put the finishing touches to a house he had lifted by more than two metres. A few years ago, he raised a 6,000-tonne church.
“When the pastor said the church would be raised by two metres, nobody in the parish believed him. They just didn’t think it would’ve been possible,” Cu recalls.
“The pastor said to me … ‘I had faith in you, but hearing what others in the parish said (worried) me.’”
Today, many people in Ho Chi Minh City want their houses raised — because not only does it flood every year during the May to November rainy season, but also the flooding is getting worse.
The city of nearly nine million residents is facing extreme weather conditions more frequently, but the infrastructure to mitigate flooding has not kept pace.
While the authorities have raised the roads, one consequence is everyone is racing to raise their property higher than the road level.
For fruit seller Tuan Hoang, who has a fruit juice stall along the roadside, frequent flooding has made it difficult to run his business.
“The water would rise here. On the road, the water would be higher than half the tyre … Where the street is lower, the water would (cover) a whole tyre,” he says.
“It’s hard for people to stop by and buy stuff.”
Population growth and rapid urbanisation have caused the city to sink as much as 80 millimetres a year during the past 20 years. But worse is to come with climate change and rising sea levels.
By 2050, parts of Vietnam’s biggest metropolis could slip underwater, according to a report by the United Nations’ Intergovernmental Panel on Climate Change.
And with some of the solutions offered by the authorities — like building a giant dyke — sparking a debate about the suitability and risks, the programme Insight explores whether one of Asia’s fastest-growing economic centres can be saved.
CHALLENGES ON MULTIPLE FRONTS
Sitting in a flat delta region, 40 to 45 per cent of Ho Chi Minh City is less than a metre above sea level. So that has made it increasingly vulnerable to heavy rainfall, storms and rising sea levels.
Many parts of the coastal city are already subject to regular tidal floods. But climate change is not the only cause of the city’s flood problems.
“The second cause is the disappearance of natural canals and green spaces that help with the city’s drainage,” says 24-year-old environmentalist Hai Long Vu Diep.
The city has grown relentlessly, adding 1.8 million residents between 2009 and 2019, not including migrants. But the density of its green space for trees is only about two square metres per person.
“It’s very low,” says Ngo Viet Nam Son, the president of NgoViet Architects and Planners. “In other (advanced) cities, that may be 10 times higher, even more.
“When the rain comes down … we need adequate green space to hold the water.”
The city, which covers more than 2,000 square kilometres, is developing so rapidly that it is also sinking, especially the chunks of built-up areas near the banks of the Saigon River, where the soil is soft.
“Those are areas that are considered problematic right now,” says Nguyen Viet Ky, who heads the Geotechnics Division at Ho Chi Minh City University of Technology. “It’s clear that there’s too much development density concentrated in weak foundation areas.”
The land subsidence can occur quite quickly when high-rises are built.
“They put a lot of pressure on the current infrastructure system,” observes Son. “When it rains heavily, you can see that the area that’s most flooded is the area that’s next to some new development.”
Another cause of subsidence is the over-extraction of groundwater, which would create underground cavities that may collapse, thereby causing the soil on top to sink.
The city’s rapid expansion has left the water supply system to play catch-up. So, while waiting for piped water, many residents and businesses have resorted to extracting groundwater.
“Thousands of (wells) — small ones, big ones, household or industrial-scale — have been built,” notes Ho Long Phi, vice managing director (operations and research) of urban consultancy enCity.
“At the highest level, we could observe more than a million cubic meters per day of total groundwater extraction during the past 20 years.”
WATCH: Why is Ho Chi Minh City sinking? (2:44)
The authorities have since put in place measures to slow down the extraction of groundwater and help prevent further subsidence.
Owing to the distribution of piped water “all over the city”, says Ky, the rate of groundwater extraction has been “significantly reduced” to around 300,000 cubic metres.
Piped water was made available to Nguyen Kim Thanh’s family just over a year ago, for example, after years of them relying on groundwater as their only source of water.
The housewife now uses the treated water to cook. But the family still pumps water from their well “to water plants and wash (their) scooters”.
The reduced groundwater extraction has been crucial, but the authorities still have their work cut out for them.
And it is not only Ho Chi Minh City that is sinking, but also the delta region of Southern Vietnam which it sits on, from the Saigon Delta to the Mekong Delta.
“The whole delta has been sinking faster than the sea-level rise,” says Nguyen Huu Thien, an independent consultant and ecological expert on the Mekong Delta. “At the hotspots, we’re sinking 10 times faster than the sea-level rise.
"So the water rises and inundates the cities along this stretch of land."
Like in Ho Chi Minh City, groundwater extraction has aggravated the subsidence. But there is also another reason.
“Because we extract sand. To build this building, to build roads, we need sand,” says Marc Goichot, the World Wildlife Fund's freshwater lead in the Asia-Pacific. “So the sand isn’t replenishing the delta.
“Even if we stop the extraction of water … the subsidence will continue. It’ll be slower, but it’ll continue. So the only way to address the subsidence is by ensuring that more sediment … is able to be deposited in the floodplains.”
Dang Nha Cong, a fifth-generation farmer in Southern Vietnam whose family’s farming tradition goes back more than 150 years, is now worried about the future of his agricultural land and its tropical fruits, even after building a barrier around it.
“Everyone here suffers from floods … Even the street gets flooded,” says the 75-year-old living near Can Tho city. “If it rises another 50 to 70 centimetres or if it rises a whole metre, I wouldn’t know what to do.
“If the farm’s flooded, all the trees will die.”
Extreme flooding would also cost Ho Chi Minh City dearly. Global consultancy McKinsey estimates the infrastructure damage a once-in-100-years flood could cause today at US$200 million (S$267 million) to US$300 million.
The estimated knock-on effects could be an additional US$100 million to US$400 million. Real estate damage alone may reach US$1.5 billion. In 2050, the economic impact could be five to 10 times higher.
HOW TO STOP THE SEA?
The threat of rising sea levels is more real for Vietnam than most others, notes Tran Ba Hoang, the head of the Southern Institute of Water Resources Research.
It is among the five countries most likely to be affected by global warming in future, according to the World Bank, in addition to the report by the UN intergovernmental panel.
“Since it’s an assessment by an international body, I think it’s a dire warning to the government of Vietnam and local authorities in areas that would be flooded owing to rising sea levels,” says Hoang.
As of now, he notes, the average sea level increase — as measured in the port city of Vung Tau for the last 40 years — is 0.45 cm per year, which he described as “relatively high”.
To protect Ho Chi Minh City and the surrounding region, authorities have proposed building a sea wall — 23 km or longer — from Vung Tau to the coastal region of Go Cong, which could cost up to US$6.8 billion.
It would help to prevent the rising sea waters from entering the delta. Ky, an associate professor, calls it a “far-sighted proposal” and “meaningful” project.
Some observers, however, believe that dykes are a “short-term” measure that alleviates the problem of rising sea levels but does not address other key issues.
“If you address the symptoms with the dyke, you don’t solve the problem — you move the problem,” says Goichot.
“Dykes stop the water from going to the floodplain. And the water going to the floodplain brings the sediment and deposits. That’s the solution.”
The high cost involved has led some analysts to question the project’s financial viability, given that dykes are also expensive to maintain as seen in the Netherlands.
“Our economic status is not like theirs … and, truthfully, the cost would be very high,” says Pham Viet Thuan, the director of the Institute of Natural Resources and Environment Economics.
"Neither the tidal angle nor the geographical features of the tidal currents in our country are the same with theirs. That’s why we can’t use a dyke to resolve the flooding."
The risk to the ecosystem is another reason to not copy the Dutch approach to building dykes, cites Goichot.
“You block the movement of nutrients, which is food for living organisms. And you create barriers to … the place where they feed or the place where they go to spawn, then you affect their life cycle,” he says.
“(The Dutch) have one of the safest deltas on the planet because they can protect themselves from floods. But now they realise that they’ve lost fisheries and lost biodiversity. And that’s a very high cost. So now they’re removing dykes.”
The Mekong Delta already has “high dykes everywhere” to protect its agricultural land, points out Thien. But that does not resolve the problem of flooding.
“When the high tide comes in from the sea, pushing the river water back … the river can’t find enough space because all the other lands are blocked by the high dykes,” he says.
“Water has to find room somewhere. So it has to find room in the urban area, in the cities, where they’re still pretty open.”
MULTI-PRONGED SOLUTION NEEDED
Despite objections to the super-dyke plan on account of its environmental and economic impacts, the project looks set to go ahead.
If it is to improve Ho Chi Minh City’s defences, however, the project would not only be costly, but also take a long time to complete.
In South Korea, the 33-km Saemangeum sea dyke and land reclamation project has taken 30 years since construction began, cites Ky. The sea wall itself needed almost 20 years to construct.
Ho Chi Minh City has barely 30 years until the results of climate change are seen in 2050. With rising sea levels, land subsidence and infrastructural shortcomings, can anything else be done to save the economic heart of Vietnam?
Hoang the fruit seller, who has often watched in dismay as floodwaters rushed down the streets in his neighbourhood, has only one choice.
“I assess how high the water is, and I raise my stall. The higher the water, the higher the stall … When it overflows, well, we have to live with the floods,” he says.
“I try to do my business as usual. It’s not as if I can quit.”
WATCH: The full episode — Asia's sinking cities: Ho Chi Minh City (48:15)
But that can only be a small part of a multi-pronged solution overall. “First, the authorities must swiftly and effectively deal with groundwater extraction,” says Diep, who is starting his master’s in resource and environmental engineering.
“Second, we must develop more green spaces and reservoirs around Ho Chi Minh City. Finally, and very importantly, the city must improve its current drainage system.”
It is about living with nature and not “trying to control nature”, adds Goichot. “We need to understand those processes and build with them. It’s not only a good, catchy concept, it’s really what we need to do.
“It isn’t so easy to implement, but it’s probably the most cost-effective way to adapt to climate change.”
Watch this episode of Insight here. The programme airs on Thursdays at 9pm.