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British weather watch

By Michael Evans - 27 Apr 2012 7:10:0 GMT
British weather watch

British Weather; Credit: Shutterstock

Since Roman times and probably before, a popular topic for conversation has always been the perversity of British weather. Until the advent of powerful computers weather prediction in the British Isles was always something of an art rather than a science, but even with modern technology accuracy is by no means guaranteed.

It is the location of the British Isles that makes accurate prediction so difficult. Situated on the edge of Europe, the prevailing southwesterly winds come from the Atlantic Ocean and are generally damp. When a North Atlantic depression hits the islands, as is often the case, heavy rainfall is the order of the day.

During the winter period, if one of these depressions should move down from the Arctic, heavy snowfall can result. Since this is often wet snow and consequently very difficult to clear, serious disruption can result.

At other times there is a completely different picture. Anticyclonic weather moving in from Northern or Southern Europe can bring intensely cold or very dry weather in winter, while a similar pattern during summer months can result in long periods of sunshine followed by drought.

An unexpected northern movement of the climatic pattern can result in unseasonably warm weather in early spring, leading to a sense of false security, since it is invariably followed by a return to normal.

Nothing is ever certain with British weather and we have now had two consecutive winters where the rainfall has been below average levels. Across Eastern England the last six months have been the driest since records began in 1921. As a result, river flows and groundwater levels are exceptionally low for the time of year, with unusually dry soils.

The low winter rainfalls and the dry soils mean that there is very little groundwater to recharge the affected areas. As plants begin to grow and the weather becomes warmer, the soils will dry out further. In a worst-case scenario a hot, dry summer would significantly worsen the effects.

As a result, in early April the UK Government announced a series of restrictions on the use of mains water in seven water companies in Southeastern England These restrictions include watering of public parks, gardens and allotments; filling swimming pools, paddling pools, ponds and fountains; and any apparatus connected to a hosepipe. Heavy fines can be imposed in cases of infringement.

As often seems to be the case in Britain, as soon as these restrictions were introduced, the weather promptly changed. We now find ourselves in the somewhat bizarre situation where prolonged heavy rainfall that has put rivers at risk of breaking their banks and flood warnings are being issued in areas deemed to be suffering from severe drought.

To compound the issue, when the ground is very hard and dry, heavy rainfall is unable to soak into the ground, causing dangerous flash floods that simply wash away the surface.

Although news of flash floods continue to come in, people living in the water-restricted areas should not count on the easing of bans on water use any time soon. Although the rain is heavy, it has done little more than dampen the soil and has certainly not produced enough to recharge reservoirs or groundwater supplies.

Indeed much of the heaviest rainfall has been in areas of Northern England and Scotland, where there is in fact no particular shortage anyway.

The national drought co-ordinator for the UK Environment Agency, Polly Chancellor, predicts that the drought could last until Christmas. "Although we have had welcome rain this week," she said, "the soil is so dry that only steady rain will restore rivers and groundwater. We urge everyone, right across the country, to help by using less water."

The Meteorological Office said that it was too early to say whether April 2012 could turn out to be one of the wettest on record, but by the month's third week in some areas it was already close to the long-term monthly average. On the other hand, according to the Centre for Ecology and Hydrology, March 2012 was the driest since 1953.

One of the problems facing those responsible for making long-term predictions is that as the year progresses, rainfall is less effective for replenishing reserves. More is absorbed by growing vegetation and much simply evaporates in the warmer weather. It is for this reason that dry winters are the real key for the prediction of summer droughts.

Two dry winters in a row, with the strong possibility of another to follow towards the end of 2012 is a real cause for concern. As the Environmental Agency's head of water resources, Trevor Bishop, pointed out, it will take more than a week or two of rain to undo the effects of nearly two years of below-average rainfall.

As for the final outcome only time will tell, but one thing is for certain, British people will always find something to say about the weather.

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