Confronting Storms & Climate Risk In HK
By Dr. Faith Chan 18 April, 2019
Typhoons have wreaked havoc in the GBA but HK can lead in building resilience, says Nottingham Ningbo's Dr. Chan; see how
In the last two summers, two fierce storm surge events from Typhoon Hato (August 2017) and Typhoon Mangkhut (September 2018) caused severe floods and other damages to Hong Kong, Macau and cities across the Greater Bay area (GBA). Intensive rainstorms, storm surges and high tidal waves led to severe floods mainly in low-lying coastal areas, with the bad experiences at Heng Fa Estate in Hong Kong East a case in point.
Storm tides induced from Typhoons Mangkut & Hato reached 3.88m & 3.57m in Victoria Harbour
These storm tides or maximum sea level induced from Mangkut and Hato reached 3.88m and 3.57m respectively at Quarry Bay in Victoria Harbour, which were only slightly lower than the historical record of 3.96m set by Typhoon Wanda in 1962 (see table below). Some other low-lying areas in Hong Kong such as Tai Po Kau recorded a maximum sea level of 4.71m (Mangkhut) and 3.77m (Hato).
Other cities in the GBA e.g. Macau, Shenzhen & the south of Guangzhou were also inundated by seawater
Other cities in the GBA, such as Macau, Shenzhen and the south of Guangzhou (Nansha districts) were also inundated by seawater during Mangkhut and Hato. As a result, many coastal infrastructures were damaged including sewage treatment plants, breakwaters of piers, beaches and harbour-front promenades.
Had Mangkhut occurred closer to the astronomical high tide period, the sea level at the Victoria Harbour could have been even higher at almost 4.9m (assuming an astronomical high tide of 2.5m). In addition, more than 100 mm of rainfall was recorded during the two typhoons, which exacerbated the conditions and caused substantial waterlogging and urban floods.
Had Mangkhut occurred closer to the astronomical high tide period, sea level at Victoria Harbour could have been almost 4.9m
The risks are not limited to water. The severe winds brought by Mangkhut (the 3rd strongest winds in history – max. gust peak speed reached 256 km/h recorded by HKO) also caused more than 60,000 fallen trees, interrupted electricity supply in more than 40,000 households, and paralysed airport and other public transport.
Mangkhut caused USD192mn of economic losses in Macau…
…while there were 2,000 insurance claims totalling HKD656mn (property & business) & HKD202mn (construction) after Hato in HK
Since the 1960s, we have experienced more than 150 severe wind incidents, with 6-7 typhoons visiting us every year on average, with severe economic consequences. In Macau, Typhoon Mangkhut caused around USD192 million losses in businesses, properties, vehicles and public infrastructures, while there were 2,000 claims totalling HKD655.7 million (property and business) and HKD202.2 million (construction) in Hong Kong after Hato.
Things could be getting worse. According to HKO, the mean sea-level in Hong Kong (Victoria Harbour) has risen about 14cm from 1954 to 2009 (an average rate at about 2.6mm per year). This rate is similar to the IPCC global projection in its AR4 and AR5 reports: which indicate a rise of 0.6 to 1.4m by the end of this century (depending on the ice-melting of the polar ice sheets and various climatic scenarios).
Hong Kong government has done well but climatic risks are rising
It has to be emphasised that the responsible institutions such as the Drainage Services Department (DSD) and the Civil Engineering and Development Department (CEDD) of the Hong Kong SAR Government have done tremendously well in the past few decades to reduce the impacts of inland and coastal floods.
Under the DSD’s management, most parts of Hong Kong can withstand “1-in-200 year floods” under the Drainage Master Plan; whilst the CEDD has also upgraded coastal flood and tidal protection infrastructures to withstand 1-in-100 year floods. These standards have kept pace with the protection levels in many Asian cities. However, we were still hit by severe flooding brought by Mangkhut, Hato, Koppu and Hugapit (the latter two in 2009 and 2008).
In the future, it remains a big challenge to Hong Kong & other GBA cities to cope…
…after all, the frequency & magnitude of coastal-enhanced floods are likely to increase
In the future, it remains a big challenge to Hong Kong and other GBA cities to cope with such climatic hazards. After all, the frequency and magnitude of coastal-enhanced floods (including seawater backlash/backflow, combined coastal and inland floods with surges and intensive rainfall all together) are likely to increase, and looking elsewhere, the recent lessons from Storm Sandy, Katrina and Harvey have raised wakeup calls that storms are powerful, that they can breach coastal defence measures, and that the impacts will exacerbate alongside with climate change and global sea-level rise.
A lack of flood risk planning & coordination between government agencies
There have already been warnings that flood risks will be growing (especially by storm-enhanced events), as current coastal flood management strategies and governance structure are still lacking. Unfortunately, the current situation in Hong Kong is still similar to nine years ago, because of two major gaps:
- In terms of planning practice, there is no authority to deal with flood risk (coastal, inland and all kind of floods) as we can see that infrastructures and new developments are still allowed to be developed on floodplains and high flood risk areas (the seawater inundation in Heng Fa Estate is an example);
- Certain government agencies have been performing impressively in their duties (e.g. CEDD with seawall constructions and maintenance; and DSD with drainage and inland flood channels) but coordination among these agencies is still lacking.
HK & the GBA could take notes from the UK’s 10-year programme to protect the Thames estuary
Mitigation on coastal flood risk is complicated as it involves multiple layers of social, environmental and economic factors. As such, Hong Kong and the GBA could take notes from the UK’s 10-year programme (Thames Estuary Asset Management 2100 Programme (TEAM2100) that aims to upgrade and refurbish London’s coastal flood defence and the Thames estuary (including the Thames Barrier and 350km of flood walls, embankments and flood gates).
This programme is designed to confront future storms and climate change scenarios until the 2100s, protecting over 1.25 million people and £200 billion worth of property from coastal and tidal enhanced flood risk. Moreover, the TEAM2100 plan is strategically designed not just to protect those exposed in London, but also those in SE England.
Collaboration among the GBA is an opportunity for long-term regional flood risk management
Recently, the governments of Hong Kong and the Guangdong-Hong Kong-Macao Greater Bay Area called for more collaboration on future social-economic developments. This is a good idea and an opportunity to establish a long-term regional flood risk management plan for the entire GBA including Hong Kong. After all, Hong Kong has had substantial experiences during the last few decades on flood management. If Hong Kong is willing to take the lead and collaborate tightly among its government agencies on flood risk mitigation and climate change adaptations, it will surely benefit the whole GBA.
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