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Friday, 15th May 2009

Weather hazards

Last week's two tropical cyclones, one in the South China Sea and the other in the western Pacific, remind us that we are once again into the rain and typhoon season.

I recently met a group of young students and asked them whether they knew how many people got killed or injured each year by tropical cyclones hitting Hong Kong. The question was put to them in multiple choices: (a) 100 or more; (b) 10 or more; and (c) a few. A majority of them picked (a) or (b). I believe many members of the public also share this view.

The casualty figures presented in Figure 1 below should dispel that impression, however.

Figure 1 : Casualties caused by tropical cyclones hitting Hong Kong during 1960-2008

The amazing fact is that the figures have gone down to only a couple of casualties in recent years. The same can be said about casualties caused by heavy rain.

So, what has happened? Three reasons can be given. One is that Hong Kong has a very robust weather warning system that is being constantly improved upon. Under this system, members of the public know how to respond in unison in their precautionary measures while the emergency services activate their time-tested operations in a well coordinated manner.

The second reason is the advance in general in weather forecasting especially in the prediction of tropical cyclones. Figure 2 below gives a flavour of how the duration of tropical cyclone warnings has on average decreased over the years. The decrease translates into less disruptions to normal life and higher efficiency for society.

Figure 2 : Number of hours with Tropical Cyclone Warning Signal Number 3 or above divided by the total number of hours with tropical cyclones within 800 kilometres of Hong Kong

The third, and by far the most important, reason is the tremendous improvement that has been brought to housing and other infrastructures over the past few decades. Gone are the days when scores of people got drowned in their sampans or dinghies, or swept away in their temporary hillside dwellings by floodwater and failed slopes.

But there is no room for complacency. First, despite its recent advance, weather forecast by its very nature is a projection into the future. It is not possible to be 100% accurate all the time. For this reason, the public should still beware of occasions with weather warnings issued at short notice and make the appropriate response.

Second, because of climate change scientists believe that storms may become fiercer and rains ever heavier. To face the eventuality of typhoons getting ever stronger, the Observatory has recently added two additional categories to the classification of typhoons, viz. severe typhoon and super typhoon, so as to heighten people's awareness towards their dangers. If we are not careful, a repeat of super typhoons like Wanda and Ruby in the 1960s or the deluges in 1966 and 1972 would still wreck havoc in Hong Kong.

While we at the Observatory spare no effort in ensuring the timely issuing of warnings, it remains imperative that people listen to the weather announcements on electronic broadcasting media, Internet and automatic telephone answering services, stay away from the hazards and take appropriate precautionary measures. Otherwise we still have to contend with people unnecessarily losing their lives in floods, high winds and in stormy waters.

In the next blog, I will talk about what other weather hazards there are around us, which may be equally if not more dangerous than typhoons and rainstorms.

B.Y. Lee

Last revision date: <17 Jan 2013>