Scientists see no need for sandstorm forecasts

PUBLISHED : Thursday, 25 March, 2010, 12:00am
UPDATED : Thursday, 25 March, 2010, 12:00am

Scientists say Hong Kong can put a better sandstorm forecasting system in place but they doubt it is worth the investment for such rare events.

Alexis Lau Kai-hon, of the University of Science and Technology, said Monday's sandstorm - which pushed the air pollution index off the 500-point scale - was an exceptional event that did not deserve more attention than roadside air pollution.

Responding to the public debate on whether the city should step up its forecasting of sandstorms, Lau said Hong Kong had the technical capability and modelling skills to do this but he doubted if the problem should be taken too seriously.

'It is questionable whether we have to invest so much time and resources for sandstorms of such a magnitude that might only come once in 10 years or more.'

He said meteorological agencies on the mainland already had rich forecasting data on sandstorms and all the city needed to do was to step up co-operation with them.

His view was echoed by Dr Fang Ming, a retired scientist who in 1996 confirmed that dust from northern China was transported to the city.

'In the past we never thought the dust could come from so far away. But in fact it happens quite frequently, though no one notices as the local background pollution is already high,' he said.

Fang said it was 'energy consuming' to forecast the impact of sandstorms that were almost unnoticeable most of the time and there was no guarantee of accuracy.

'Technically, prediction is possible but whether it is socially desirable is another matter.'

He also proposed better networking with meterological bodies on the mainland or Taiwan. Fang recalled how his research team collected dust samples near Tung Chung and in Sai Kung in May 1996. 'We thought we had made a mistake when we found the samples were yellowish. But soon we knew we had hit the jackpot.'

Fang said air pollution index data they collected later showed an unusual rise in pollution concentrations similar to what happened to Hong Kong on Sunday night. Chemical analysis on the samples also confirmed the origins of the dust.

Lau said strong winds that blew up fine dust in northern China to a height of more than 2,000 metres hit Beijing earlier this month. A westerly wind then took it to Korea and Japan. A region of high pressure in the north also created a clockwise rotational motion that swept the dust south near to Shanghai and then out towards the sea. The dust moved down the east coast of Taiwan on Sunday, then an easterly wind pushed it over Hong Kong. Dr Mark Wenig, of City University, said a good sandstorm forecast required reliable meteorological information, a weather prediction model, satellite images and computer modelling. The whole process was very complicated.

A spokesman for the Observatory said they were still in discussions with the Environment Bureau over future forecast of sandstorms and it was too early to say what would be adopted.

The Observatory said the city was not hit by a sandstorm in the strictest sense, since visibility never dropped below one kilometre.

In response to media reports that northern China will have six to nine sandstorms in two months, the Observatory said it could not tell now if they would affect Hong Kong. There is no official sandstorm warning or forecast issued on the website of the National Meteorological Centre.