SciDev.Net

Clouds over Thailand

NASA Johnson Space Center - Earth Sciences and Image Analysis

Cloud seeding is a technique used to ease drought by spraying chemicals, ranging from silver iodine to salt and dry ice, into clouds to increase rainfall.

The chemicals cause vapour droplets to freeze into snow, which melts as it falls to the ground. In regions with pronounced wet and dry seasons, the technique helps overcome drought.

In this article, Paris Lord reports that agricultural officials in Thailand say that cloud seeding more than 1,000 times in less than one month has eased the toughest drought in seven years by 80 per cent.

Using a technique patented by the Thai king Bhumibol Adulyadej, two aeroplanes spray their chemicals into warm and cold clouds at different altitudes to make rain over a wide.

Thailand's success has led countries including Cambodia and Oman to ask for technical assistance to help relieve their own droughts.

As Thailand considers how best to help, it has warned that cloud seeding only works with suitable clouds and when the humidity is higher than 60 per cent. Also, it cannot do much to ease extreme droughts.

Cloud seeding experiments have been taking place for more than 60 years and the technique has been applied successfully in several countries including Australia, China, Malaysia and the Philippines.