Studies show much of Hong Kong's reclaimed land is at risk of being claimed back by the sea around the beginning of the next century. A report by Wang Yuke

The world's coastal cities, our own Hong Kong among them, are under threat of being swamped by the rising seas, spurred by global warming and melting of polar ice caps. Hong Kong is likely to be spared the initial onslaught of submersion that will strike coastal areas like New York City, the Maldives, Kiribati and Tuvalu in the next 15 to 30 years. Hong Kong's hilly topograAn. "But still, parts of the city are at risk of being submerged in the future," predicts Benjamin Strauss, director of the program on sea level at Climate Central based in New Jersey, United States.

"By the end of the century, chronic flooding or submergence will threaten places in Hong Kong where 200,000 to 385,000 people live today," he told China Daily.

Those alarming figures place Hong Kong at No 18 among the world's top 20 places at risk of submersion. The sea is rising to take back its own from those 6,000 hectares (based on government maps and charts), reclaimed by Hong Kong authorities to create developable land for a land-strapped city.

More than 20 hectares of the Central Business District, including the Hong Kong Central Station Airport Express Terminal, are on reclaimed land. Hong Kong Disneyland, Tuen Mun, Sha Tin, West Kowloon, the Hong Kong International Airport and other sites sit on reclaimed land as well.

Reclamation began in earnest during the 1890s. Reclaimed land turned almost vertical after 1967, when urban development mushroomed.

Dykes and seawalls soon will have to be erected to prevent floods brought on by rising tides. The alternative is to build up previously reclaimed land, raising them above sea level, says Strauss.

"Global sea levels have risen roughly eight inches from 1880 to 2009. That rise occurred because global warming accelerated the melting of land-based ice into the oceans, and because seawater expanded as it absorbed heat from the warming atmosphere," wrote Union of Concerned Scientists (a US advocacy group) analyst Erika Spanger-Siegfried, climate scientist Melanie Fitzpatrick and consultant Kristina Dahl in their study, "Encroaching Tides", released in October 2014.

The rate of global warming slowed down during the past 15 years. Global mean temperatures rose by only 0.09F per decade, according to statistics released in 2013 by the Intergovernmental Panel on Climate Change (IPCC) based in Switzerland. That compares with statistics showing a steady increase of 0.21F per decade between 1951 and 1998.

The hiatus is predicted to be short-lived. The brief cessation of global warming may be explained by the ocean's having reached its capacity for absorbing heat. Rising temperatures brought about by greenhouse gases affect the ocean more profoundly than other parts of the planet. Ninety percent of the heat energy generated by the greenhouse effect from 1971 to 2010 was absorbed by the ocean, according to the IPCC report.

South China Sea temperatures were erratic - caused by El Nino besides the combined effects of winds, waves, ocean currents and other factors.

The El Nino factor

"Situated at the South China Sea, Hong Kong is subject to that interplay between El Nino event and ocean dynamics," said Gan Jianping, professor in the Division of Environment at Hong Kong University of Science and Technology.

Gan pointed out that other factors affecting ocean dynamics include ocean salinity, water temperature, density of seawater and ocean depth. If the most active ocean dynamics were to combine to raise the highest tides, during an acute El Nino event, a major flood could seize Hong Kong without notice, at least in theory, reveals Gan.

A scientific enquiry led by Benjamin Strauss shows that the increase in sea level in the century between 2000 and 2100 in Hong Kong is projected at between 1.23 m and 1.50 m in the worst scenario in which greenhouse gas emissions maintain their present rate.

"If the pristine sea is likened to a huge bath tub, reclaimed land resembles a shallow washbasin," says Gan. "Whenever a typhoon strikes, an aggressive tide will follow. Then the powerful storm will generate an even greater tide, technically called a storm surge. That major influx of water could be handled by a bath tub, but it (the "storm surge") must spill out of a diminished washbasin."

"Artificial lands reclaimed from the sea often have high risk from a rise in sea levels which causes flooding, even in mountainous areas," Strauss says.

"North Point and Quarry Bay appear to be uplifting slightly, while Tai Po Kau is sinking," says Robert E. Kopp, associate professor of the Department of Earth and Planetary Sciences in Rutgers University in New Jersey, United States.

"Between 2000 and 2100, under business-as-usual conditions, Tai Po Kau is very likely to experience a rise in the sea level of between 0.50 m and 1.40 m. Any significant abatement of greenhouse emissions would bring down the increase in sea-level to 0.30-1.0 m." But the rise in sea level will not cease when the calendar changes to 2100. Kopp projects the increase could grow to between 0.80-2.60 m by 2150. "The West Antarctic Ice Sheet might collapse quicker than we expect. Under such a worst case scenario, Tai Po Kau could experience up to a 2.90 m increase in sea levels by 2100."

Tai Po has been somewhat notorious as the most flood-prone area of Hong Kong in past decades. In July 2010, a total of 225mm of black rain associated with Typhoon Chanthu poured down on Hong Kong. Rivers rose 1.20 meters in half an hour.

Reclamation drive on

Despite warnings from record temperatures and rising sea levels, the Hong Kong government shortlisted six potential sites for reclamation in 2013. The list includes Lung Kwu Tan at Tuen Mun, Siu Ho Wan on Lantau Island and Ma Liu Shui in Sha Tin, Tsing Yi and Sunny Bay.

Hong Kong International Airport sits on reclaimed land, covering 12.48 square kilometers between Chek Lap Kok and Lam Chau islands. Floods could pose an enormous threat to the low-lying airport, causing irreversible disaster.

Climate scientist Strauss says "airports are commonly built in low, flat areas next to the water, and face a great threat from sea level rise. Commonly, one of the first threats from sea level rise in large coastal cities is to their airports." Again, the lurking danger seemed to have fallen under the radar. The construction of a third runway for the airport was approved this year on 650 hectares of reclaimed land.

The Airport Authority acknowledges the risk from extreme tidal conditions and other adverse elements. "We have ensured that the upcoming runway is designed accordingly with respect to the statutory standards and regulations. The potential rise of sea level by climate change has also been taken into consideration," says Vincent Lui, a spokesman for the Airport Authority. He offers the reassurance that "the airport at Chek Lap Kok was built on reclaimed land, and has been operating smoothly since 1998."

Before the submergence projections are fully realized, there are steps that can be taken to mitigate the damage that threatens Hong Kong. "Rezoning low-lying land and moving unsafe and critical infrastructure to higher ground and construction of low wave reflection sea walls" would help, says Kalmond Ma, head of climate program of WWF Hong Kong.

He says the vertical sea walls used for protecting Victoria Harbor are flawed as they could cause a ricochet effect. But low wave reflection sea walls not only prevent powerful wave from breaching the sea walls, but also help to curb flooding and limit coastal erosion.

Contact the writer at jenny@chinadailyhk.com

Land reclamation, like here at Central, continues apace in Hong Kong. The city is rated No 18 among the world's economies most at risk of submersion.  Edmond Tang / China Daily

An aerial view of Hong Kong International Airport , which is potentially at risk from rising sea levels.

(HK Edition 10/21/2014 page7)