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Monday, 13th July 2009

Weather hazards (2)

In a previous blog on weather hazards, we talked about the dangers of tropical cyclones and rainstorms. These are obvious to people who live in Hong Kong long enough. However, there are other less obvious weather hazards which nonetheless can kill.

I am referring to lightning and high winds brought about by thunderstorms when the sky is gloomy, and to heat strokes when the sky is clear.

Lightning

Figure 1 below presents the casualty figures associated with lightning in Hong Kong in recent years.

Figure 1 below presents the casualty figures associated with lightning in Hong Kong in recent years


There were 39 casualties during the period from 1990 to 2008, including 6 deaths (or 0.3 death per year).

To enhance safety in this aspect, the Observatory implemented a lightning location system in 2005. Various products of lightning information are available on the Observatory website and its automatic telephone answering system. The latest product is a location-specific service which enables an alert to be automatically sent to the user whenever lightning is detected within a specified distance from a location chosen by him/her.

High winds from thunderstorms

While people know that tropical cyclones can bring windy conditions, the danger of high winds brought about by thunderstorms is often overlooked among the local public. The associated casualty figure as extracted from press reports is given in Figure 2.

The associated casualty figure as extracted from press reports is given in Figure 2


The casualty figure is 28 over the past 8 years, caused by capsized boats/ships, broken trees, and fallen containers, neon signs, windows and scaffolding. The figure includes 6 deaths, or 0.8 death per year which is more than that associated with lightning.

There are inherent difficulties in accurately predicting the gusts from thunderstorms. To heighten alertness, the Observatory has enhanced the wind and gust information and prepared dedicated webpages and automatic answering phone messages to warn people of the high winds.

To mitigate the damaging effect of high winds from thunderstorms, however, it is very important that members of the public are aware of the relevant safety precautions. Operators, contractors, and engineers should also ensure that outdoor structures and machinery are properly secured and attended to by the time the Thunderstorm Warning is issued.

Heat strokes

Hardly any year goes by without casualties associated with heat strokes. As shown in Figure 3, although the record is not long, the casualty figure (suspected to be suffering from heat-related illnesses) as extracted from press reports is quite high: 325 over the period 2005 to 2008, including 23 deaths which amount to 5.8 deaths per year. This is many times the figures for the previous two weather hazards.

Heat strokes


A majority of these incidents happened to people engaged in outdoor activities. Some of these people were often young and still in their productive years.

The press reports did not state the medical causes for the casualties. There can be many factors associated with a heat stroke. In Hong Kong, the weather factors can be: high temperature, high humidity, and no wind. Non-weather related factors include physical fitness, state of dehydration, amount of rest prior to exercise or work, pre-existing chronic disease, etc.

What complicates the matter is the fact that some incidences might have been triggered by the heat, but the ultimate death causes were something else, unrelated to weather. Despite this, the casualty figure certainly requires greater attention.

Together with relevant parties, the Observatory is actively studying the matter using available weather data in Hong Kong. The task is not simple, but hopefully some useful heat-stress information can be developed for the public over the next couple of years.

In the meantime, the public is advised to pay attention to the Very Hot Weather Warning as well as the regional temperature information issued by the Observatory, and take extra care in protecting themselves under hot weather.

Outdoor workers should heed the advice of the Labour Department:
http://www.labour.gov.hk/eng/public/oh/heat.pdf.

B.Y. Lee



Last revision date: <17 Jan 2013>