Sinking Cities

Sinking Cities

Rising sea levels caused by climate change, coupled with land subsidence, are an urgent challenge across Asia.

Heavy machinery is deployed to sink concrete poles along the shoreline off Bang Khunthian district of Bangkok to prevent coastal erosion. About 400 electricity poles were taken from areas in Bangkok where power lines had been laid underground. They were placed vertically to form a buffer zone against the waves. (Photo by Pawat Laopaisarntaksin)
Heavy machinery is deployed to sink concrete poles along the shoreline off Bang Khunthian district of Bangkok to prevent coastal erosion. About 400 electricity poles were taken from areas in Bangkok where power lines had been laid underground. They were placed vertically to form a buffer zone against the waves. (Photo by Pawat Laopaisarntaksin)

One of the most pressing challenges the world is facing as a result of climate change is rising sea levels. Scientists predict that oceans will rise by between 0.3 and 2.5 metres by 2100. This will put many coastal areas at risk, with potentially catastrophic consequences for large cities.

Of the 10 major cities most threatened by rising ocean levels, seven are in Asia. Topping the list is Jakarta, which has seen changes of up to 3 metres in some areas in the past three decades (the figure is a combination of the increase in sea level plus the rate of land subsidence). If current trends continue, Jakarta will be the first to remind us of Atlantis.

To provide a better perspective, 40% of the Jakarta metropolitan area of 30 million people is now below sea level. Only a 60cm wide seawall keeps the Java Sea from flooding the city. This is one of the reasons why the government has decided to move the capital to East Kalimantan province on Borneo by 2024.

"The threat of rising sea level just keeps increasing," John Englander, president of the International Sea Level Institute and author of High Tide on Main Street, told Asia Focus. "The rise is global but certain cities are sinking faster, making the problem more urgent, with Jakarta being a prime example."

Average sea levels have risen by 23 centimetres since 1880, with 7.5cm of that rise in the last 25 years, according to a recent National Geographic article. The recent report by the Intergovernmental Panel on Climate Change (IPCC) predicts that sea level will rise between 30 and 80cm between now and 2100.

With an estimated 54% of Asians inhabiting low-lying coastal areas, governments and environmental agencies have been goaded into action to arrest land subsidence and take other measures to prevent a Waterworld scenario.

The battle will be difficult and expensive. Creating a new capital in Indonesia to ease the pressure on Jakarta will cost an estimated US$32.7 billion -- but it won't do anything to directly address land subsidence and rising water. That could cost another $40 billion, the budget approved for constructing artificial islands as a buffer against the Java Sea, as well as a vast coastal wall.

In Singapore, protecting the city-state against rising sea levels could cost $72 billion or more over 100 years, Prime Minister Lee Hsien Loong said on Aug 25.

Unlike its Southeast Asian counterparts, Singapore does not face a direct threat of land subsidence from rising sea levels. In the worst-case scenario, if global temperatures increase by 4C and sea level rises 9.5m, 745,000 Singaporeans could be submerged, out of a population of 5 million. However, the government is all hands on deck in case to stop the country from sinking.

Singapore has introduced a carbon tax and will require future critical infrastructure such as new airport terminals and ports to be built on higher ground. Earlier this year, the government said it would spend S$400 million over the next two years to upgrade and maintain drains and strengthen flood resilience. Its plan also includes building polders or reclaiming islands offshore and connecting them with barrages.

Since 2011, land reclamation projects in Singapore have raised the mean height of 3 metres above sea level to 4 metres. Nicholls Drive, which surrounds Changi Airport, was been raised by 80cm. Work has been done to fortify coastal areas with seawalls and rock slopes, while sandbags have been laid at strategic locations to prevent land erosion.

CLOCK TICKING

In Thailand, Bangkok has long been known as the "Venice of the East" for its extensive network of canals, but like its Italian counterpart, it is facing increasing risk.

When Bangkok was established, its canals were well above sea level. However, many are now below sea level. A study by the National Reform Council in 2015 showed the city risks being submerged in less than 15 years if nothing is done. A World Bank study predicts that 40% of Bangkok may be engulfed by waves in as early as 2030.

According to Anond Snidvongs of the Geo-Informatics and Space Technology Development Agency (GISTDA), much of Bangkok is already lower than sea level, and the city sinking by one to two centimetres every year.

In Indonesia, the Maritime Affairs and Fisheries Ministry estimates that the country loses 1,950 hectares of coastal land annually -- an area equal to the West Sumatran city of Padang Panjang. The 895 hectares of new beaches formed each year from sedimentation do not offset these lost lands.

North Jakarta is already seeing regular inundations from high tides, having sunk 25cm in the past decade. A recent BBC report showed a two-storey office building in the district of Muara Baru sitting mostly under stagnant water. Studies say the northern part of Jakarta may be completely engulfed by 2050.

West Jakarta is estimated to be sinking at an annual rate of 15cm. The rate is 10cm in the eastern part of the city, compared with 2cm and 1cm, respectively, in Central and South Jakarta.

Manila, the sprawling capital of the Philippines, is currently sinking at a rate of 10cm annually. In the worst-case scenario, Manila may have to cope with 2-metre tides by 2100 if greenhouse gas emissions remain unchecked and global temperature soars by 5C, affecting 62% of the Philippine citizens who inhabit low-lying coastal areas.

"Since the city has an average elevation of around 5 metres, it seems to be living on borrowed time," the authors of the 2018 Christian Aid report Rising Seas, Sinking Cities, wrote about Manila.

The underlying cause of Manila's problem is unchecked usage of water from groundwater sources. Much of the unregulated water utilisation involves water-intensive rice paddies in the suburbs, golf courses and swimming polls. The expansion of fish farming has further exacerbated the situation.

The Philippine government has undertaken land reclamation projects around Manila, but scientists and planners fear these projects will only increase urban sprawl, putting more pressure on water resources.

Vietnam, meanwhile, ranks third in percentage of land lost to erosion and natural disasters since 1961 (4.7%), behind St Kitts and Nevis (25.7%) and Ecuador (10.3%), according to a Statista infographic produced last year. Ho Chi Minh City is particularly at risk. Gilles Erkens from Deltares, an independent institute in the Netherlands, says the most populous city in Vietnam has sunk by 50cm over the past 25 years.

South Ho Chi Minh City is currently 160cm below sea level, while the highest tide was recorded at 172cm. Le Van Trung, vice-president of the city's Geomatics Association, has conducted extensive studies of the districts of Binh Chanh, Binh Tan, Nha Be, Thu Duc as well as Districts 7, 8 and 12. His assessments concluded they are sinking by 0.5 to 1cm each year.

"It is estimated that by 2070, sea levels will have risen by 50cm," he said. "Without swift action, the subsidence combined with rising sea levels will put enormous pressure on the city's drainage system and flood defences."

Hanoi is also suffering from land subsidence, attributed mainly to groundwater extraction by its growing population.

IMPACTS BEYOND SUBMERSION

According to the Global Risks Report 2019 by the World Economic Forum, Asia will be the worst affected region in the world from sea level rise. Population displacement is one of the largest concerns. The World Bank says a one-metre sea level rise could displace 37 million people, while a three-metre rise would displace up to 90 million people.

This could lead to a migration crisis if cities are unable to cope effectively, especially when infrastructure, services and employment opportunities in smaller cities and rural areas are not ready to cope with the influx.

Another major impact will be the loss of arable land, given that Southeast Asia produces 88% of the world's rice supply with much of that used for domestic consumption. This will result not only because of inundated farmland, but also from increased salinity levels that will render agriculture unviable.

In Vietnam, saltwater could intrude as much as 40km inland in the Red River Delta, leaving high levels of salt in what would otherwise be productive land.

There will also be inevitable economic costs. According to the Asian Development Bank, natural disasters arising from climate change could cost the Philippines, Thailand and Vietnam 6.7% of gross domestic product (GDP) each year over the next century. Then there is the potential losses of $864 billion in built assets that could be swept away by sea level rise in 23 Asian cities.

PREVENTING DOOMSDAY

What can be done to prevent large areas of land sinking under rising seas? Is there a common solution that all countries can use to combat land subsidence?

In Southeast Asia, the sheer weight of building structures above ground contributes to subsidence. Excess groundwater withdrawals are also a threat in many Asian metropolises. According to a study by Binaya Raj Shivakoti from the Institute for Global Environmental Strategies (IGES), over one billion citizens in the region rely on groundwater for domestic use. This over-reliance accounts for 68% of global groundwater withdrawal, making Asia the largest groundwater user. In addition, 30% of Asia's groundwater is sourced directly from aquifers.

Several viable solutions exist to resolve or at least mitigate the challenges posed by climate change. Many countries may look to emulate the low-lying Netherlands, famed for the effectiveness of the dikes, levees, pumps and dunes that have been erected along its coastline in order to hold back sea level rise. Indeed, a Dutch architect has called water engineering "the principal export of the Netherlands". Jakarta has already started building a seawall with the help of Dutch engineers.

Sea walls come with their own shortcomings, however. They simply deflect energy to nearby areas, and they are also prone to failure, which could lead to catastrophic consequences. They also pose a risk to marine life which may come up against what used to be soft shorelines.

Another solution is replanting mangrove forests, many of which were cut down to make way for today's Asean megacities. Research by the University of Southampton has shown that mangroves can help with decreasing erosion and preventing water from moving farther inland.

A more radical idea is to build amphibious structures. Prof Wong Poh Poh from the University of Adelaide in Australia, told The Straits Times that Singapore should build homes that are anchored to the ground but can float when flooded.

If all else fails, an option is the relocation of populations. While Indonesia is moving its capital away from sinking Jakarta, moving as many as 1.5 million government workers, their families and those employed in related activities to a new site will be a mammoth undertaking.

Ultimately, any solution will require a high degree of government initiative and involvement. Many experts feel that governments across Asia Pacific are not yet alert enough to the risks posed by sea level rise, and have done little to stem the impacts.

A good place to start, in Mr Englander's view, is by making changes in building codes and zoning to anticipate future flooding. "Flooding is getting worse now from heavy rain and strong storms," he said. "Over the next 30 years when sea level rise accelerates, it will lead to worse flooding."

He suggests developers and builders must plan their projects to withstand one to two metres of flooding as a matter of routine. Structures and infrastructure that are more critical and expensive should be planned even more conservatively.

"Even without government action, individuals and businesses can also build in anticipation of worse flooding in the future," he pointed out.


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