As many as 1.2 billion people, about a third of Asia’s population, face the risk of flood damage.

The heightened risk of flooding and other water hazards in the world’s growth engine may also hinder economic recovery in the post-pandemic era.

In early October, Thailand’s Chao Phraya River spilled its banks, inundating temples and houses near Bangkok.

In one area where floodwaters reached waist-high, a 55-year-old resident said the water was “two to three times higher than usual”.

Major floods are frequent in Asia, aggravating the problem of land subsidence, where the ground sinks.

A research team at the University of Rhode Island in the US conducted a satellite survey to measure the rate of land subsidence in 99 cities worldwide between 2015 and 2020 and found that 17 of the 20 fastest sinking cities are in Asia.

The biggest drop, at just over 52mm a year, was observed in Tianjin, China.

Extensive subsidence was also observed in big cities in Southeast Asia, including Jakarta, at 34mm, and Bangkok, at 17mm.

“Without measures to address subsidence, many areas could experience major flooding sooner than expected,” said Meng “Matt” Wei, an associate professor at the university’s graduate school of oceanography.

In fact, while sea levels have been rising by just over 2mm per year worldwide due to global warming, the land has been sinking at rates five to 20 times faster.

Subsidence occurs when too much ground water is extracted for daily living and industrial use.

Because many big cities in Asia are on lowlands in coastal areas or near river mouths, just a few centimetres per year of subsidence can cause serious damage if left unattended.

In Indonesia, more than 60% of Jakarta is said to already be below sea level.

“In some areas of North Jakarta, subsidence ranging from 15cm to 25cm a year is occurring which, if sustained, would result in these areas sinking to 4m to 5m below sea level by 2025,” the World Bank said in a report.

Impoverished, politically unstable countries are the most vulnerable to disastrous floods.

More than 1.8 billion people in the world are exposed to such risks, of which 1.24 billion, or 70%, reside in South and East Asia, according to a report released in June by senior World Bank economists and others.

Economic losses from water damage have been growing, with damage from weather disasters, such as floods and heavy rainfall, totalling US$1.38 trillion in 2010 to 2019, up nearly 50% from the previous decade through 2009, according to the World Meteorological Organization.

Torrential rains and flooding have hit Pakistan since mid-June, submerging a third of the country and affecting 33 million people.

With damage estimated at US$40 billion, Pakistani climate minister Sherry Rehman called the flooding an “unprecedented climate catastrophe”.

In Bangladesh, China and India, more than 100 people have died as a result of the heaviest rainfall in decades.

If natural disasters hit poverty-stricken areas inaccessible to aid, their impacts will linger, according to the World Bank.

The cause of land subsidence is not limited to groundwater extraction, but varies from fluvial sediment supply to channel dredging, said Thai oceanographer Anond Snidvongs, adding, “We should also look at measures to counter land subsidence, on both small and large scales, such as landfill (or) land levelling that are done without control, blockade of waterways and floodways, artificial ground water recharge … (taking) these actions without a thorough understanding may cause more harm to the environment and human society than land subsidence,” he warned.

Japan showed more than half a century ago how effective policy can arrest land subsidence.

During the country’s period of high economic growth from the 1950s to the 1970s, Tokyo experienced one of the fastest subsidence rates in the world, with land sinking 20cm a year in some areas.

But the sinking stopped after the country introduced laws and ordinances to restrict ground water extraction.

Some countries are now resorting to much more drastic measures.

Indonesia, for example, will begin moving its capital to Nusantara, a new city on the east coast of the island of Borneo, in 2024.

The relocation was spurred in part by severe land subsidence in Jakarta, according to the Indonesian government.

If countries in Asia want to maintain growth, they must find ways to halt land subsidence and make their cities more resistant to floods and other natural disasters.