HUA HIN High above Thailand's parched landscape the kingdom's fleet of intrepid royal rainmakers work their meteorological wizardry.

A squadron of 20 aircraft plunges through the clouds firing a cocktail of chemicals that they hope will provoke a downpour to alleviate the effects of drought on the country's crucial agriculture sector.

The annual cloud seeding operation is something of a personal crusade for Thailand's King Bhumibol, who has earned the title “Father of the Royal Rainmaking” for his half-century project to persuade clouds to rain on cue.

Not content to leave the weather in the hands of nature, the octogenarian monarch developed the programme to support the country's farmers and has even patented his own cloud seeding technique.

In a manoeuvre known as the “sandwich”, the king's rainmakers fire chemicals at different altitudes - such as sodium chloride above and dry ice below - to induce rainfall from warm clouds.The “super sandwich” adds another aircraft to the operation, releasing silver iodide from about 20,000 feet - around 6,000 metres - to initiate rain from formations of varying temperatures.

Pilot Major Phumintorn Undhisote flies from the rainmaking centre in Hua Hin, where the king has his holiday home.

Seeding in this narrow strip of the country between the Gulf of Thailand and the Myanmar border takes a high level of precision. And while Major Phumintorn believes in the effectiveness of his missions, they are not without risk.

“According to the flying textbook, in bad weather pilots have to fly away... or land, but rainmaking means we have to fly into the clouds,” he said.

He is one of 522 people - including scientists, engineers, pilots and technicians - involved in the Bureau of the Royal Rainmaking and Agricultural Aviation's efforts to manipulate Mother Nature.

More than 5,500 cloud seeding flights were made from eight centres in 2008 and around 870 million baht (27 million dollars) was spent on the project.

This year the rainy season - normally from about May to October depending on the region - got off to a weak start. While Thailand has a tropical climate and suffers floods as well as drought, the size of the agriculture sector and growing consumer demand for water makes the country particularly sensitive to the vagaries of the wet season.

Figures from the country's central bank suggest agriculture accounted for almost 10 per cent of the economy last year and nearly 40 per cent of the labour force.

Wathana Sukarnjanaset, director of the Hua Hin cloud-seeding centre, said there had been “quite a crisis” this year, with water in some of the country's biggest dams falling to critical levels, although the situation is improving.

In the most recent dry season, from November through April, 6.4 million people in 52 provinces were affected by drought, according to the Department of Disaster Prevention and Mitigation.

In the past, cloud seeding was dismissed by some as little more than meteorological alchemy as scientists struggled to assess whether rainfall would have happened regardless of chemical assistance.

But it has gained a mainstream following in many countries, including the United States and China, while Thailand recently gave Australia permission to use the king's techniques.

Wathana said Thailand's own research suggested cloud seeding can increase precipitation by 109 per cent.

He said there was usually “quite a change in the weather” after the flights, which operate from February to October.

“Farmers come to ask us to make rain in that area so we tell them 'go back and wait' and it is raining in the afternoon (or) in a short time, one or two days mostly,” he added.

One of those who relies on the cloud seeders is Siriwan Boonngarm, whose farm nestles deep in the Phetchaburi countryside.—AFP