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Last Updated: Thursday, 18 May 2006, 12:07 GMT 13:07 UK
Would cloud seeding ease the drought?
By Finlo Rohrer
BBC News Magazine

HOW CLOUD SEEDING WORKS
Graphic showing how clouds are seeded
1. Fire silver iodide into cloud using flares on planes or from ground
2. Water droplets attach to these particles, falling as snow which melts into rain
3. This boosts updrafts, which pulls moist air into clouds

With lawns going brown and cars left unwashed, can we make it rain by firing chemicals into the clouds, a technique reportedly used during the 1976 drought?

It has only taken a few weeks of drought panic for the blue-sky thinkers to come up with seemingly outlandish plans such as towing icebergs up the Thames.

But while one such idea - cloud seeding, also known as weather modification - sounds like the stuff of science fiction, it dates from the 1940s. Particles are dropped or fired into clouds in an effort to change levels of precipitation.

Its best known use is in Moscow, where legend goes that it never rains on Red Square on May Day. It's a practice that still goes on today.

"It wasn't raining in Moscow [this May Day]," a spokeswoman for the mayor says. "We have a 'making the weather' department."

Water disputes

In China it's credited with boosting rainfall in drought-stricken areas, although there are allegations of "rain theft" levelled at provinces that use it too zealously.

Ground-based cloud seeding device
It's used to boost snowfall
It's used to boost snowfall in the mountains above Californian hydroelectric dams, at Colorado ski resorts, to stop fog at airports and to prevent hail damage in cities.

Don Griffiths, president of North American Weather Consultants, says the first step is to take a cloud with upper layers below freezing. Next fire silver iodine (or salt or dry ice) into the cloud. This can be done either by dropping flares from a plane - these may be attached under the wings - or fired from the ground.

Water droplets attach to the particles forming snowflakes. Once these are heavy enough, they fall as first snow then melt into rain at lower altitudes.

"The trick is getting those seeding materials in the right place at the right time," says Mr Griffiths.

Experiments show that rainfall can be boosted by at least a quarter in specific areas over a whole season, he says. As for whether the UK could benefit, that depends on the type of clouds in the affected areas.

Ongoing controversy

Many meteorologists agree that cloud seeding brings more rain, but the issue of whether it can be increased in any predictable way remains controversial.

Clouds being seeded in summer
There is no technology that can create rain when there was no potential for it to begin with
Keith Seitter
American Meteorological Society
The US National Academy of Sciences has called for more research, driven by a world in which two billion suffer water shortages. But, it warns in a recent report, "scientists are still unable to confirm that these induced changes result in verifiable, repeatable changes in rainfall, hail fall, and snowfall on the ground."

And Keith Seitter, executive director of the American Meteorological Society, also adds a note of caution.

"There is no technology that can create rain when there was no potential for it to begin with. Cloud seeding appears to be able to get a little bit more than you would have got otherwise. The conditions are going to have to be just right for cloud seeding to have a measurable impact."

For there are annual variations in rainfall, variations even scientists cannot explain.

Wrong sort of clouds

Stephen Dorling, senior lecturer in meteorology at the University of East Anglia, says it's difficult to imagine finding a reliable way to boost rainfall.

Reservoir in southern England
Reservoirs are running dry
"The difficulty is doing it in a controlled way. The process of rain formation is reasonably well understood, but as far as a computer programme that can model it, each cloud has an incredible amount of science going on inside it. We simply wouldn't have the computer to handle it."

He's also worried that cloud seeding could provoke legal disputes between nations, if rain was increased in one area but reduced in another.

But Mr Griffiths dismisses suggestions that cloud seeding could harm other areas.

"There is a huge amount of water vapour in the atmosphere. It is like an ocean but you think of it as a small lake. Only 10% of the water vapour ever reaches the ground as rainfall or snowfall."

Whether or not southern England has the right sort of clouds, the authorities regard talk of cloud seeding - and iceberg towing - as a distraction.

"Banning non-essential use is the priority," says an Environment Agency spokeswoman. "We do not currently need to even consider extreme measures."


Add your comments on this story, using the form below.

One major problem is flushing the toilet with perfectly clean drinking water! There should be new plumbing systems installed that dont waste such water.
Sam C, London

We help Third World countries overcome the fact they have no water, so why can't we help ourselves? I find it stupid that a country as advanced as ourselves have come to this situation, but yet nothing is done about it and we will be in the same situation again next year. Stopping people from using the water is not going to solve the problem and especialy giving out fines... it just creates a bigger distance between the goverment and the people.
Richard, Northwest

Perhaps water can be condensed out of the hot air spouted by politicians explaining away the need to upgrade the distribution network to prevent leaks ?
Anon, UK

The country has gone mad, would it not be easier and cheaper in the long run for the water companies to patch the leaks? How much profit have they made recently?
Tony Smith, London

Brilliant, not only is there going to be a drought with lawns going brown but they're also going to poison the water course. In fact this reminds me of a similar story that came out of glastonbury festival one year where they reckoned they had a cloud buster to stop it raining. You watch next thing they will have men on the moon.
Guy Parkinson, Dewsbury

I thought this was a joke. We are dealing with global warming, icecaps melting and they are talking about pulling icebergs up the Thames. Surely with the amount of rain England actually gets we could erect large temporary water tanks in rain fall area. And if the water companies actually repaired damaged pipes correctly we wouldnt see leaks for weeks on end.
Amanda, Leeds, Leeds

I read only yesterday how the Thames Valley area, managed mainly by Thames Water, has the worst leakage record in the country, co-incidence they are imminently considering a non essential drought order. Are slack water companies being fined, or considered for take over, threatened with nationalisation, or someone fixing prices till their abysmal record improves, that'd kick start investors into action!
Chris, Oxford

I think we need some more info on 'iceberg towing'. It sounds like genius!
Russell, Bristol

Why expend time and money on these idea in England when so much of the rain the does fall is wasted?? How much water is lost by the water companies through leaks? Water meters should also be mandatory, my house in Australia like all homes their has one. I could see the effect simple measures had on my useage. Like Lord Kelvin said, you can't manage what you can't measure. Management of the resource is needed not just more of it!
Matthew, London

For goodness sake, maybe we should be considering wider issues here, such as why so many people live in the south.....we don't struggle for water in the North....ummm less people, less stress on the system...better quality of life (dare I say?)
Naomi, Durham, UK

Although cloud seeding might seem like a good idea at first has anybody considered the real costs. Not just financial but enviromental as well. Surely it would be better to put more effort into capturing eccessive rainfall water for later use and fixing old and damaged pipes. Use the money from shareholders to build more reservoirs and desalination plants. Divert rivers that are prone to flooding into reservoirs instead of straight out to sea. With a little thought and investment now in years to come we could be selling water to real drought stricken areas and boost our nation's income. A far better way keep the tap running.
Chas, Southampton

I have been a mariner all my life and have noticed that 40 years ago weather depressions transited well to the north, over iceland. Today we see them touch the tip of Scotland as they travel east, and the highs rarely form over the UK any more. The Gulf stream therefore must have moved to the south more closer to Scotland, so based on the time it has taken to reach this point, it will not be too long before we loose the benifits of the Gulf stream, Then we will have all the water we want in the form of ice,
Jim Evans, brighton uk

Cloud seeding was reported to cause disastrous flooding in North Devon - the govt would have to think really carefully before doing this!
Duncan McCarthy, Bristol,UK

Cloud seeding is wrong - you are just interfering with a natural cycle. The rain that is bought about by seeding obviously stops that rain from falling naturally elsewhere. Nowhere near enough is known to re-attempt this folly.
Ian, England

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