HO CHI MINH CITY: Vietnam's largest city Ho Chi Minh is sinking by an average of two to five centimetres a year and this has resulted in the city suffering more frequent flooding.
According to a new study conducted by Japan International Cooperation Agency (JICA), the city has been constantly sinking since 1990, with the total subsidence now estimated at 100 cm.
In the study that was carried out in collaboration with local state agencies, they found that the current rate of subsidence averages two to five cm per year and in areas with many high-rise buildings, the rate was seven to eight cm per year.
The Vn Express reports that according to the Division for Water Resources Planning and Investigation for South Vietnam, the city had sunk 23 cm from 2005 to 2017.
The subsidence was highest in An Lac ward of Binh Tan district, where it subsided by a whopping 81 cm.
The study also revealed that the top 10 localities experiencing the worst subsidence are Districts 2, 7, 8, 12, Go Vap, Tan Binh, Binh Thanh, Phu Nhuan, Binh Tan and Thu Duc.
HCMC University of Technology (HCMUT) had also been monitoring the subsidence and its research showed that between 2006 and 2020, several areas in Districts 12, Go Vap, Tan Binh, Binh Thanh, Phu Nhuan and Binh Tan were most affected, with the highest subsidence rate recorded at 43 cm in 15 years, an average of three cm per year.
The JICA has been carrying out its research with the help of the Vietnam Institute of Geosciences and Mineral Resources, the Water Resource Institute under the Ministry of Natural Resources and Environment, and the Southern Institute of Water Resources Research under the Ministry of Agriculture and Rural Development and the Saigon Water Corporation (Sawaco).
The Vn Express report said the agency has proposed HCMC cope with subsidence based on the experiences of Jakarta and Tokyo.
As Jakarta is sinking at an alarming rate, the Indonesian government has decided to move its capital to Kalimantan. It is projected that by the middle of this century, one-third of the Indonesian capital will be underwater.
To handle the situation in the Vietnamese southern metropolis, various government departments are now assisting JICA to draw up a subsidence response plan within the fourth quarter of the year.
In 2019, a United States-based non-profit news organisation Climate Central, said most of southern Vietnam, including the Mekong Delta and the nation's economic hub HCMC, could be flooded by 2050, similar to Jakarta.
It said that sea levels would increase by one metre by 2100 and this could potentially flood about 18 per cent of HCMC and 39 per cent of the Mekong Delta.
Various organisations have said that many cities were expected to be affected by rising sea levels in Asia. Among them are Chattogram in Bangladesh and Semarang in Indonesia, and Manila.
Most of these areas have subsidence rates of more than two cm per year, which is 10 times higher than the global mean sea level rise of two mm per year.
According to the coastal science Hakai Magazine, researchers found four cities with more than 1,000 sq km of land below 10 m elevation, were sinking quickly. The four areas are Shanghai and Tianjin in China, Hanoi in Vietnam, and Bangkok in Thailand.
The researchers also found another 18 cities throughout the world with between 100 and 1,000 sq km of fast-subsiding, low-elevation areas.
Japan's capital Tokyo managed to drastically reduce its subsidence problem when authorities introduced better groundwater management.
The Tokyo Metropolitan Government had introduced pumping regulations for the thousands of wells in the capital area in order to slow and reverse the pace of land subsidence.
Manila is also facing a similar problem and calls have been made for strict regulatory measures to reduce groundwater extraction.
The Philippine capital has been subsiding by more than two cm per year between 2015 and 2020. This is almost seven times faster than the average sea level rise.