Rainmakers linked to SAR deluge

PUBLISHED : Thursday, 19 September, 2002, 12:00am
UPDATED : Thursday, 19 September, 2002, 12:00am

The torrential downpours that soaked Hong Kong this week coincided with a rainmaking operation in which aircraft sprayed chemicals on clouds blanketing Shenzhen.


More than 400mm of rain fell in Hong Kong between Sunday and Tuesday, leaving the territory's reservoirs 90 per cent full, even though the Observatory initially forecast only scattered showers.


Over the same period, officials in Shenzhen sent planes into the sky to distribute rain-inducing chemicals, a process known as cloud seeding, prompting speculation that it may have caused Hong Kong's downpours.


The Hong Kong China News Agency said that the authorities in Shenzhen carried out the operation because they were concerned about drought conditions in some of its neighbouring areas.


Residents in Shenzhen were deluged with rain over the same three-day period this week.


One of them, a 28-year-old accountant, said yesterday: 'We read about the rainmaking operation and a lot of people have been wondering if the very heavy rain is because of it.


'We heard Hong Kong had been getting some of the same weather and we suspect the whole process might have worked better than the people responsible expected it to.'


However, experts yesterday said the cloud seeding operation was probably not to blame for the heavy downpour in Hong Kong. Scientific officer for the Observatory, Wong Wai-kin, attributed the Hong Kong deluge to a low air pressure system over the South China Sea.


The associate dean of science and engineering at City University, Johnny Chan Chung-leung, said it was unlikely that cloud seeding over Shenzhen would have caused rain as widespread as that which hit Hong Kong.


Rain vapour in clouds needs a particle around which to form a raindrop heavy enough to fall to the ground, he said. In nature, dust can act as the particle but, in cloud seeding, chemicals such as silver iodide play the role instead.


The Commonwealth Scientific and Industrial Research Organisation in Australia concluded in a recent paper that cloud seeding in its experience was effective only in a limited number of weather conditions.


The mainland is one of the world's biggest users of cloud seeding, and spent more than 243 million yuan (HK$229 million) on weather modification attempts in 2000.


At least two workers were killed in Shenzhen yesterday when a landslide caused by torrential rain buried the makeshift shelters they lived in near a petrol station at the Meilin checkpoint.


The China News Service reported last night that the landslide had taken place shortly after lunchtime. Rescuers found 30 transient workers at the scene and two were dead before they reached hospital.


The report said rescuers were still searching for survivors at the site last night.


 

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