- The post-rain collapses have killed hundreds in the city, much of which is made up of slopes
- Now the custodians of its hillsides want to notify people of the dangers, and of ways to stay safe
Hong Kong could develop its first early-warning system for landslides, using a new index which gives the risk of the potentially deadly collapses following rainstorms, a top government engineer has said.
The Landslide Potential Index, one of the only such metrics in the world, estimates the risk of landslides in the city based on the intensity and location of rain and the distribution of slopes, the Geotechnical Engineering Office (GEO), which is responsible for the upkeep of hillsides, said.
Hong Kong, where more than 70 per cent of land is made up of slopes, has a history of tragic landslides, with more than 470 fatalities in the 50 years from the end of World War II. In 2018 more than 250 landslides were reported, the highest number in a decade.
"We already have the technology in place to have an early-warning system for landslides, but we also need to make sure people understand the risks and what to do to be safe," GEO head Pun Wai-keong said.
There is only so much we can do to prevent landslides with engineering. That is why we are trying to educate residents, and the index can decrease fatalities by up to 80 per centPun Wai-keong, Geotechnical Engineering Office
Ratings on the updated index, introduced in October, are posted online within five minutes of the end of a rainstorm and updated every five minutes. The index gives the risk of landslides from 0 to more than 100, with 10 to 50 being high-risk, 50 to 100 very high-risk, and more than 100 extremely high-risk. After each rainstorm, the risk decreases over time.
The previous index took up to two weeks to calculate and did not have a numbered scale, which was neither user-friendly nor easy to understand, Pun said.
The office gets an average of 300 landslide reports each year, most triggered by storms. Between 1985 and 2018 there were three rainstorms which would have triggered a landslide potential index warning of more than 100 under the new system, according to government statistics.
Of the three storms, the highest rated on the updated index scored 126, coming after a heavy storm on June 7, 2008, which triggered 347 landslides in areas around Lantau Island and the University of Hong Kong, killing two people.
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A 1994 storm which triggered a fatal landslide on Kwun Lung Lau estate in Kennedy Town killed five and injured three, and would have had an index of 103.
The third storm rated above 100 killed one man in Fu Yung Shan after a rainstorm on Aug 20, 2005.
But Pun warned that although Hong Kong has been "quite lucky" in recent years " particularly during Typhoon Mangkhut, which brought more wind than rain " projections showed that extreme weather could cause up to 9,000 landslides across the city.
"If something on the scale of Taiwan's deadliest Typhoon Morakot in 2009 hit Hong Kong in the future, we could see 4,000 to 9,000 landslides and extensive damage to infrastructure and roads," he said.
"There is only so much we can do to prevent landslides with engineering. That is why we are trying to educate residents, and the index can decrease fatalities by up to 80 per cent," he said.
Pun said residents should avoid hillside areas, and stay on the second floor if they live near hills, after heavy rain.
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