Whither weather?

March 7, 1997

The wettest February has followed the driest January. THES reporters look at the changing climate. THE storms that claimed the lives of seven people in one night were severe by any reckoning. But were they merely freak conditions - or the latest signal that something odd is going on with the weather?

Many weather watchers are focusing on extreme events and radical fluctuations in temperature and rainfall. Researchers at the Institute of Hydrology, for instance, say that this year's figures are breaking records at two extremes. This January was the driest in England and Wales since 1769. February has more than made up for it, however.

The institute's Terry Marsh predicts a dramatic contrast: "I shall be surprised if February's rainfall is less than twice the average for the United Kingdom, making the month one of the wettest this century."

The data seem to confirm anecdotal evidence that forecasts frequently have more than a hint of melodrama about them. And the January/February contrast is by no means a one-off. Wide and sustained departures from the normal seasonal variations have been detected by Dr Marsh over eight years. In 1995 the second-driest August on record was followed in parts of southern Britain by the second-wettest September.

Academics like Tim Burt, professor of geography at Durham University, agree that the weather has been particularly extreme. "Things are volatile at the moment. We are seeing unusual fluctuations from very wet to very dry periods. What is this a sign of? Global warming? Yes, but we don't know yet whether this is the greenhouse effect," he said.

Average temperatures over the seven years to 1995 are the highest on record, and for the past 20 years when taken as a block, temperatures have been 0.5 degrees centigrade greater than the average for the preceding 20 years.

Dr Marsh believes the past ten years have been pushing at the limits of historical variability. "It is fair to assume the goalposts are moving," he said. He points out that climatic instability and Britain's continuing vulnerability to unusual weather patterns has been underlined by a number of notable flood and drought episodes.

Such droughts, when considered in the context of historical rainfall, are exceptionally rare, he said. But the clustering of droughts over the past 20 years has now called into question the ability of historical data to provide an accurate basis for the design of water management strategies.

Apart from the obvious water supply implications, experts are looking at the environmental impact of global warming as it subtly changes Britain's climate and triggers wild fluctuations in rainfall and temperatures.

Researchers at Durham University's environmental research centre believe that Britain's wildlife may already be under threat.

Ecology lecturer Bob Baxter is involved in research into extreme weather events which may result from climatic warming, and in particular their impact on wildlife. A significant proportion of the work is centred on the North Pennines around the Natural Environment Research Council's flagship site in the Upper Teesdale national nature reserve.

Long-term data on weather, climate, flora and fauna are being analysed. The project combines studies of plant and insect physiology with their population dynamics to predict responses to climate change.

Dr Baxter said there was still inadequate global data to determine accurately how weather extremes have changed during this century. But global models were being scaled down to show regional trends, and there was good evidence for changes in some extremes at regional level - for example, in the incidence of frosts and droughts.

The concern is that such extreme events may trigger the local extinction of vulnerable species as vegetation adapts to climate change,.

The Case Moth is one example. Failure of its food supply through altered local temperatures results in the disappearance of the moth and its reappearance depends on its ability to re-colonise.

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