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Rainmaking efforts ease drought

Planes take off almost every day over Thailand's dried-out rice paddies with a chemical cocktail that scientists -- guided by Thailand's king -- hope will wring the clouds dry and ease a drought that has scorched southeast Asia.

The propeller planes are packed with up to seven people including the pilot, scientists and technicians, all squeezing in around large containers of chemicals ranging from silver iodine to ordinary salt and dry ice.

Flying at about 3,000m over parched fields, dusty dams and thirsty rivers, the planes fly directly into clouds that most pilots avoid so scientists can dump their loads and wait for rain.

Thai agricultural officials say those rainmaking efforts -- known as cloud seeding -- have worked and eased the toughest drought in seven years by 80 percent.

The reported success has led countries from Oman to Cambodia to ask Thailand if the method used here could ease periodic droughts in their countries, but scientists warn that cloud seeding works only in certain circumstances.

Besides, cloud seeding has a history which stretches back more than six decades and results of experiments around Asia have been mixed at best and appear more likely to cushion a drought's impact than break it.

Thailand has used cloud seeding for almost 30 years, led by King Bhumibol Adulyadej, who has his own patented rain-making technique.

Rainmaking begins when the relative humidity exceeds 60 percent. Lower humidity makes the efforts harder, Wathana Sukarnkanaset, director of Thailand's bureau of royal rainmaking and agricultural aviation, tells AFP.

The chemicals are sprayed into clouds to encourage smaller clouds to merge and induce rain. The cocktail causes tiny vapor droplets to coalesce and the water freezes into snow which melts as it falls.

The king's technique uses two aircraft to seed warm and cold clouds at different altitudes to make rain over a wider area than other methods, Wathana said.

Flights by BT-67s, Nomads and Cessna Caravans are held almost daily and last up to two hours, depending on the aircraft's size and the target area.

With Thailand's drought pinching, the air force, police and navy loaned the agricultural ministry additional planes, giving scientists a total of 45 aircraft for cloud seeding, Wathana says.

The rainmaking bureau has 600 staff and a budget of almost one billion baht (US$25 million), though expanded operations this year and rising fuel costs could force them to request more money, Wathana says.

Like much of the rest of the region, Thailand receives lots of rain -- more than 1,200mm a year in most areas and up to 4,000mm in some coastal provinces.

But the rain doesn't fall evenly across the year, causing a cycle of droughts and floods, made worse this year by the exceptionally harsh dry season ahead of the rains that normally begin in mid-May.

"Our technique tries to help distribute rain for the whole season," Wathana says.
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