By Finlo Rohrer
BBC News Magazine
HOW CLOUD SEEDING WORKS
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
3. This boosts updrafts, which pulls moist air
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
"It wasn't raining in Moscow [this May Day]," a spokeswoman for
the mayor says. "We have a 'making the weather' department."
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.
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.
It's used to boost
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.
Many meteorologists agree that cloud seeding brings more rain,
but the issue of whether it can be increased in any predictable way
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.
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
Reservoirs are running
He's also worried that cloud seeding could provoke legal disputes
between nations, if rain was increased in one area but reduced in
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
"Banning non-essential use is the priority," says an Environment
Agency spokeswoman. "We do not currently need to even consider
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
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 ?
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
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
I think we need some more info on 'iceberg towing'. It sounds
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!
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?)
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.
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,
Cloud seeding was reported to cause disastrous flooding in North
Devon - the govt would have to think really carefully before doing
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.
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