45 5 Preparedness and Resilience • Warnings and response for storm surges HKO currently provides storm surge forecast to the public and special users mainly with reference to the tropical cyclone forecast track and the worst-case scenario. Risk-based and impact-based products based on the probabilistic forecast are being tested, which could support emergency response decision-making of possible storm surge scenarios at specific locations out to several days ahead that could be converted into a risk matrix. The protection measure adopted in Tai O was a successful example of enhancing the resilience of a vulnerable community against storm surge impact due to extreme weather. Subsequent to the storm surge inundation of Tai O during Severe Typhoon Hagupit in 2008, the government put in place both hardware (polder scheme consisting of riverwall and demountable flood barriers) and software (an emergency response plan) to protect the village. The response plan kicks into the place whenever the predicted sea level at Tai O exceeds the 3.3 mCD threshold. Tai O residents and relevant supporting organizations will be notified, DSD will install the demountable flood barriers to form a flood protection zone, and various disciplinary forces will help evacuate residents. The plan proved effective during subsequent typhoons, such as Super Typhoon Hato of 2017. HKO’s new risk-based storm surge foreast noted above, currently under internal trial, can enhance the precision of mobilization of the Tai O response team. FIGURE 5.3 Risk-based and impact-based storm surge forecast concept Source: HKO HKO’s operational storm surge prediction system “SLOSH” EC EPS 51 ensemble tracks Probabilistic forecast of tidal height at a specific location Risk-based storm surge forecast (under internal trial with DSD) KOMPASU (2130) Water levels from 2021-10-11 00:00:00 (HKT) to 2021-10-13 03:40:00 (HKT) at QUB station 10-10 23:50 10-12 23:40 – – 10-12 00:10 10-12 22:50 – – 10-11 23:30 10-12:22:30 10-13 01:30 – 10-10 23:00 10-12 21:20 10-12 22:20 10-13 00:13 Water levels (mCD) 0.75 0.50 0.25 0.00 Probability Low Medium High Very high Runtime UTC : 10-11:00 Storm size : 112km
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