As of November 21st, high tides in Ho Chi Minh City have reached their peak, surpassing the level-3 warning threshold - a level that signals a high risk of severe and prolonged flooding. According to weather forecasts, water levels could reach between 1.65 and 1.70 meters
But rising tides is not a new phenomenon. The difference now is that the city’s ground level is gradually sinking, lowering the threshold at which flooding occurs. Even a slight rise in the tide can immediately submerge areas that are already low-lying.
In other words: It’s not that the water is rising too fast - it’s that the city itself is sinking too quickly.
The second fastest sinking city in the world
Ho Chi Minh City is facing widespread land subsidence and flooding, placing it as the second most at-risk city among the world’s top 10 fastest-sinking cities.
Research from the University of Natural Resources and Environment shows that between 2006 and 2020, the city’s ground level dropped by an average of 2–5 cm per year. In some areas, where the soil is weak or commercial buildings are densely concentrated, the land is sinking even faster: up to 7–8 cm annually.
Cumulative subsidence since 1990 has reached approximately 1 meter according to a recent survey by the Japan International Cooperation Agency (JICA), . The land subsidence rate is about twice as fast as sea-level rise, which is roughly 1 cm per year.
In many areas, such as Nha Be, Binh Chanh, and Binh Tan, residents have to raise their homes regularly to keep up with the sinking land. At An Lac Ward (old Binh Tan district) the cumulative subsidence from 2005 to 2017 has reached 81cm, far above Ho Chi Minh City’s average subsidence of 23 cm.
As the ground continues to drop, even minor tides and seasonal rains can cause severe flooding, disrupting daily life and putting pressure on the city’s infrastructure. In flood-prone areas such as Tran Xuan Soan and Huynh Tan Phat Street in old District 7, residents prepare by placing sandbags and other items to raise their homes above the water - often with little success.
Four reasons why the city is sinking
According to the Ho Chi Minh City Department of Agriculture and Environment, there are four main reasons why the city is sinking.
- Areas sinking more than 10 mm per year are often built on weak soil, even without the impact of construction, traffic, or groundwater extraction.
- Locations with heavy trucks, tankers, container traffic, or urban railway lines tend to sink faster due to the constant pressure on the ground.
- Houses, apartments, and high-rise buildings can affect the soil, but thanks to modern foundation techniques, most of this impact is temporary, and the ground usually stabilizes over time.
- Excessive groundwater pumping and widespread concrete surfaces prevent rainwater from replenishing underground aquifers, lowering groundwater levels and causing the land to sink. Before 2010, this was one of the main reasons for the subsidence. But since then, the authority has restricted extraction permits, which significantly slowing the rate of subsidence and stabilising previously affected areas.
What to do with it?
Several potential solutions have been suggested to slow or prevent further sinking of the city. Research team led by Assoc. Prof. Dr. Le Trung Chon, Director of the Institute for Sustainable Development, University of Natural Resources and Environment proposed using geospatial regression analysis to forecast land subsidence rates in Ho Chi Minh City, based on subsidence time-series data obtained from InSAR techniques, combined with geological data and groundwater data.
With this predictive data, Ho Chi Minh City will be better equipped to respond promptly, make informed decisions, adapt effectively to climate change, and pursue sustainable development.
Assoc. Prof. Dr. Ho Long Phi, former Director of the Center for Water Management and Climate Change (Vietnam National University, Ho Chi Minh City), said that the city needs to strengthen its flood control system, such as building dikes, river embankments, tide gates, and high-capacity pumping stations to manage water during the rainy season and high tides proactively.
In the short term, he also noted that Ho Chi Minh City should focus on resolving obstacles to complete ongoing projects, particularly the nearly VND 10,000 billion tide control project, which is now over 90% complete. Once in operation, this project will play a crucial role in controlling flooding in the city center and the southern areas, which are low-lying and have weaker soil compared to other parts of the city.