More summer storms point to global warming
From: Psalm 110 (SatansLiars_at_SwiftRepugs.org)
Date: 08/18/04
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Date: Wed, 18 Aug 2004 07:27:06 GMT
http://www.nzherald.co.nz/storydisplay.cfm?storyID=3585140&thesection=news&thesubsection=world
More summer storms point to global warming
18.08.2004
1.00pm - By MICHAEL McCARTHY
Increasingly severe summer rainstorms like the one which led to the
flood which devastated Boscastle, Cornwall on Monday are beginning to
suggest the influence of global warming, a leading flood scientist
said yesterday.
Climate change is predicted by supercomputer models to cause more
violent summer downpours in Britain - but such is the variability of
our climate that no single storm can be taken as conclusive evidence
of it.
However, the increasing occurrence of such events is now starting to
point to global warming as the ultimate cause, said flooding expert
Professor Alan Werrity.
Speaking in the aftermath of Boscastle, Professor Werrity, who is
adviser to the Scottish Executive on sustainable flood management,
said that it was difficult to detect an upward trend of extreme
climatic events against a background of high climatic variability - or
as scientists say, to "separate the signal from the noise."
However, most climate scientists were increasingly confident that a
signal was starting to emerge, he said.
"You would find very few experts who would say that what happened at
Boscastle is unequivocal evidence of climate change," said Professor
Werrity, who is Professor of Physical Geography at the University of
Dundee.
"One can't point the finger at a particular event and say, this proves
it.
"However, it is consistent with it. And taking event after event, the
more frequent and more intense storms affecting Britain suggest that
it is very likely that climate change is beginning to register. My
feeling is that a signal is beginning to emerge from the noise."
While the popular conception of global warming is of increased heat,
it is increased precipitation that may be of much more consequence for
Britain.
The predictions from supercomputer models of the future global
climate, like that run by the Met Office's Hadley Centre for Climate
Prediction and Research at Exeter, are that as the present century
progresses, Britain will experience increasing winter rainfall,
especially in the north and west, and summer rainstorms of increasing
force all across the country.
Britain is already situated in a meteorological "battle zone", where a
mass of warm air coming up from the tropics meets a mass of cold air
coming down from the pole, Professor Werrity explained.
With global warming, the intensity of the encounter between these two
converging air systems is predicted to increase, and more storms will
be generated. The warmer the air, the more moisture it can hold -
which will eventually fall as rain - and the more dynamic are the
atmospheric processes.
The result: a soggy future for Britain.
This may present a severe challenge to the public, to policymakers and
to Governments, Professor Werrity said yesterday.
We will often get very wet in the summer, he said, but more seriously,
cities which will experience many more intense storms than they have
in the past will be unable to cope with the run-off from the streets.
"The Victorian sewer system we have wasn't designed to cope with the
rainfall intensity we are experiencing today and which will become
even more violent in the future," he said.
"The urban drainage can't evacuate the run-off from the storms, and in
a city if you can't get rid of the water quickly enough through the
drains, then the drains back up."
This happened in London only two weeks ago, leading to a massive
discharge of untreated sewage into the River Thames, which killed many
thousands of fish,
However, re-engineering the Victorian sewer system across the country
would cost many billions of pounds, Professor Werrity said, and it was
unrealistic to think that this money would be spent, as urban drains
are the responsibility of the privatised water companies, and the
official water regulators would be unlikely to allow water prices to
be put up high enough for the companies to cover the costs.
There was a partial solution in SUDS - sustainable urban drainage
systems, a technology that is trying to replace impermeable street
materials such as asphalt and concrete with surfaces which allow
rainwater to pass through them into the soil - but this was applicable
mainly to new developments.
There would also be an increasing problem with steep river valleys,
like that of the Vallency which overflowed at Boscatle, and the Lyn at
Lymouth which flash-flooded with heavy loss of life in 1952.
"If you have thin soils and a steep slope to the river and its
tributaries, then it's inevitable that the amount of rainfall that
fell at Boscastle [60mm] in two hours is going to produce a very large
and rapid rise in the river," he said.
"It might be an event to be expected once in a hundred years. The
amount that fell at Lynmouth was thought of as once in 500 years. But
these frequencies are certainly going to change."
In planning regulation, we would have to be much more robust about
allowing building near riverbanks in areas which are at increasing
risk, but it was impossible to predict exactly where extreme events
might occur.
"The difficulty is that events of the Boscastle severity are almost
random in time and space," he said.
"Here was an intense storm which could occur almost anywhere is
southern Britain. On this occasion by chance it was right over
Boscastle, but the likelihood of it being in any particular place is
really very small. So thinking of it from a policy point of view, it's
almost impossible to predict that a given settlement is going to
experience a flood of that magnitude within ten to twenty years."
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