Climate change

Hong Kong is not unprepared for extreme weather and rising sea levels, but Typhoon Mangkhut shows defence can be stepped up

PUBLISHED : Thursday, 27 September, 2018, 6:02am
UPDATED : Thursday, 27 September, 2018, 6:02am

I refer to “Weather warning” by Chandran Nair (September 22) and in particular his statement: “The city has not implemented any plans to deal with the effects of climate change. It has not built sea walls, nor changed building codes for coastal buildings to account for storm surges.”

This statement somewhat ignores the 2018 Port Works Design Manual (Corrigendum No 1/2018), issued by the Civil Engineering and Development Department, which requires all maritime structures design to take account of climate change and especially sea level rise. The requirements for storm surge assessment have also been revised. The manual already included allowable wave overtopping discharge quantities for the safety of people, vehicles and buildings. Furthermore, any maritime design engineer worth his salt has been taking into account sea level rise for the last 10 years or so, based on the Intergovernmental Panel on Climate Change guidelines.

It is unfortunate that this corrigendum will need a review of the very high wind speeds, recorded during Typhoon Mangkhut, in comparison with the manual’s extreme predicted wind speeds, typically used for wave generation and storm surge height estimates, which were probably exceeded during the typhoon.

Mr Nair’s assumption that the enhanced East Lantau Metropolis will put people and land at risk of flooding is also dubious, as the sea walls and land levels will be specifically designed for extreme event typhoon waves and surges. Clearly such measures will be more expensive, as he states, but the land sales, government rates and rent will more than pay back the costs far quicker than some recent infrastructure developments.

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The island will shelter other, currently exposed, urban areas of Hong Kong from typhoon waves and it is far more likely to reduce storm surge heights within the harbour than increase them. The combination of the island, perhaps coupled with a storm surge barrier, similar to the Thames Barrier or the Venice barrier, on the typhoons’ eastern approaches to Hong Kong, should be modelled hydrodynamically to select the best options. Such solutions are likely to be far more cost-effective than having to raise kilometres of sea walls and harbourfront land.

In short, with our concrete houses and tower blocks, we are much better prepared than in America, where they continue to build houses made of sticks, even after the wolf has visited numerous times. Therefore, let the relevant government departments plan a holistic and cost-effective defence from future typhoons, but hope they get on with it.

Jonathan Meigh, Sai Kung