By Paris Lord
Bangkok - 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 south-east 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 rain-making 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 rain-making and agricultural aviation, tells reporters.
The chemicals are sprayed into clouds to encourage smaller clouds to merge and induce rain. The cocktail causes tiny vapour 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 rain-making bureau has 600 staff and a budget of almost $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.
In late March, at least 60 of Thailand's 76 provinces were hit by drought, causing low dam levels that shut down hydro-electric plants, forcing farmers to stop irrigating second crops and water officials to restrict supplies to several hours a day in some areas.
The millions of acres of ruined fields cost more than $189.2-million, the interior ministry says.
After nearly 1 100 cloud seeding flights from March 15 to April 9, enough rain had fallen to ease the drought in at least 80 percent of the affected areas, according to the ministry of agriculture.
Sixteen provinces remain drought affected, five of them seriously.
But measuring how much rain fell by cloud seeding, and how much fell naturally is difficult.
US-based cloud seeding specialist William Woodley, who worked with Thai scientists on rainmaking projects in the 1990s, says that "carefully crafted cloud seeding has been shown to enhance rainfall in Thailand".
But he warns that no cloud seeding methods can succeed without suitable clouds.
"In periods of extreme drought, there is not much that can be done for rainfall enhancement. The key is to employ cloud seeding when suitable clouds are present such that the enhanced rainfall is available in reservoirs during periods of drought."
Encouraged by Thailand's experience, Cambodia has asked Bangkok for cloud seeding help, with 14 of its 24 provinces hit by the drought and up to 700 000 people suffering from food shortages due to poor rice crops.
Thailand's government is considering how best to respond to the request, but has been asked by countries from around the region for technical assistance and demonstrations of the Thai technique.
Thailand and Cambodia are among the hardest-hit of seven countries baking in the drought, but Vietnam and parts of southern China, Malaysia, Laos and Indonesia and are also suffering.
Malaysia holds annual cloud seeding operations between April and May, but this year began in March to boost water supplies in the northern states of Perlis and Kedah, the country's "rice bowl".
The Philippines began cloud seeding in 1997 in the Visayas, and today uses the technique in major farming areas such as northern Luzon and the southern island of Mindanao.
The department of agriculture in Manila said operations have in some areas cushioned the impact of long dry spells, especially in Mindanao.
In China, meteorologists combat increasing water shortages, particularly in Beijing, by pouring rainmaking chemicals from aircraft, or shooting them into the sky using rocket shells and anti-aircraft guns.
Between 1995 and 2003, China spent $266-million on rainmaking efforts in 23 provinces and regions, state press reports said.
Australia, the world's driest continent, began cloud seeding experiments in the late 1940s. Because of varying results, the Commonwealth Scientific and Industrial Research Organisation, Australia's top science body, stopped tests in the 1980s, having concluded the technique was ineffective at breaking droughts.
Two areas in Australia still use it - the Snowy Mountains in New South Wales state for snow, and the southernmost state of Tasmania for water.
During its first season last winter, snow in the Snowy Mountains project increased by 25 percent, officials said. - Sapa-AFP