The rainmakers take to the skies

Three new radars will give researchers a better chance than ever before of determining whether controversial cloud-seeding technology actually works.

Research into cloud seeding has been carried out in the UAE for ten years but an update to the country's weather radar system could finally help scientists properly evaluate the success of the project

Views of the UAE from the wing of a plane involved in cloud seeding

Courtesy National Centre for Meteorology and Seismology.
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You rain-dance and it rains. Surely, then, the dance made it rain?

Maybe not. But while rain-dancing is obviously optimistic, several governments, including the UAE's, have in recent years put their faith in controversial cloud-seeding technology to bring more rain to parched soil.

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They, like the rain-dancers, have a problem: if it rains after a "cloud-seeding" event, how can they be sure whether one caused the other?

Now scientists are hoping that a facelift of the country's weather radar system will finally be able to dissipate the cloud of uncertainty and prove once and for all that their technology works.

Three new radars and an upgrade to the existing network will make researchers better equipped than ever to tell whether a rainstorm was directly augmented by a cloud-seeding event or not.

Since 2001, meteorologists in the UAE have been looking at the possibility that firing flares containing salt into clouds could make it rain.

"The science says that cloud seeding can enhance the rainfall by 10 and 15 per cent," said Omar Alyazeedi, director of the research and development at the National Centre for Meteorology and Seismology.

"We hope that we are doing that, but there's currently no way to verify whether we are succeeding or not."

The formation of rain in a cloud is a complex process. Vapour coalesces into water droplets around seed particles, known as cloud condensation nuclei, which can be as small as 0.2 microns - one millionth of a metre - in diameter.

Droplets can form around many different types of particles that circulate in the atmosphere, such as salt, dust or soot. They are collectively known as aerosols.

Cloud seeding works by using large particles of salt that are more conducive to the process of coalescence, also known as hygroscopy.

The particles are fired into clouds from aircraft-mounted flare guns at a height of over 2,000m. The seeding takes place at a crucial stage of the cloud formation known as convection, when warm air rises and cools to the point that water vapour particles clump together.

Cloud seeding is most effective in the summer months, as convective clouds can be sighted 40 to 50 times over mountainous areas both in the north of the country and in Al Ain - compared with five to 10 occasions during winter months.

Rain over the mountains is more helpful, too, as it does more to replenish groundwater supplies than rain over the desert - thanks to the wadis, which act as natural repositories. Between 2003 and 2005, several UAE studies have attempted to determine whether cloud seeding actually worked.

But, according to Roelof Bruintjes, a meteorologist with the National Centre for Atmospheric Research (NCAR) in Colorado, and one of the leading authorities on weather modification, the results were inconclusive.

"It's been a little bit of a mixed bag," said Mr Bruintjes. "Under some conditions there have been increases of 20 per cent in rainfall.

"But depending on the background particles that are there at a certain time, cloud seeding may have a different impact than on other days."

Evaluating a project, he said, requires both a large number of cases where seeding took place and cases where it did not.

However, the number of variables in the UAE - such as sea breeze, dust storms and various types of particle matter - made it impossible to get a clear picture.

"There was more natural variability than we expected," he said. "The sample size was not sufficient to get a statistically significant result."

Mr Bruintjes is also the chief executive of Advanced Radar Corporation, a US firm that is providing the new radar systems to the UAE. The first will be installed next week. The radars use a dual-polarisation technology - different from a traditional Doppler radar in that they emit microwaves that are polarised in two planes, horizontally and vertically.

That enables particle matter in clouds to be detected more clearly, letting scientists more clearly determine how rain droplets are formed in clouds - and measure the success of a seeding event.

"If you do cloud seeding you would be able to see some signatures in the cloud and see whether the precipitation is really developing more efficiently," he said.

There are only a handful of dual-polarisation radars in the world and only once before has one been used to evaluate the success of cloud seeding.

That was in 2009, when NCAR carried out research in the Brisbane area on behalf of the state government of Queensland, north-eastern Australia.

"It showed a lot of promise back then," said Mr Bruintjes. "That's something we're also keen to try in the UAE."

The two new fixed radars, in Al Ain and Abu Dhabi, along with one mobile radar unit, will work alongside the existing system of five Doppler radars that date back to the 1990s, based in Abu Dhabi, Delma, Dubai, Al Ain and Fujairah.

An upgrade to the existing radars this year will increase their sensitivity, allowing them to detect dust storms or sea breezes.

Mr Bruintjes and other NCAR scientists will also be carrying out new research in the UAE on how aerosols affect cloud seeding.

In addition, the team will study whether other materials could seed clouds more effectively than salt. "We'll be starting from scratch at the laboratory level," he said.

Earlier this year, reports claimed that a company called Metro Systems had built a system of giant lampshade-like structures in Al Ain that emitted negative ions purported to trigger rain.

A UAE-based scientist connected with weather modification confirmed that ionising technology had been tried but abandoned. "We didn't have any success with this," said the scientist, who declined to be named.

Hardly surprising, said Mr Bruintjes, who considers ionising technologies to be speculative at best. "There's no scientific basis to that," he said. "I'm very sceptical. All physics is against it. People are desperate, so they will pay anyone to make water."