FOREST fires and drowned fields, unprecedented water shortages and devastating floods make it seem as if the weather has gone crazy.

A large area of Europe, from Switzerland to Bulgaria, has been battered by days of torrential rainfall, setting off floods that left more than 40 people dead amid widespread destruction.

Romania has been the worst affected, with authorities putting the death toll at 31 yesterday. In Switzerland six people were reported killed and four hundred in the town of Brienz had to be rescued from their homes.

Bavaria, in southern Germany, remains on flood alert and the Government has said that it expects the damage from the floods this week to exceed €100 million (£68 million).

Meanwhile, Spain and Portugal are being roasted in a record-breaking drought and blistering heatwave, which has set huge tracts of forest ablaze and left water supplies perilously low. At least 15 people have been killed and up to 140,000 hectares destroyed. More fires broke out in Portugal yesterday. In Britain, a drought in the South and East has been replaced by persistent downpours. This week’s deluges have exceeded the usual rainfall for the whole of August.

The reason behind the mayhem is the jet stream. A few miles high in the sky, this wind races around the Earth like a river, reaching speeds of more than 200mph and travelling eastwards — which is why transatlantic flights are quicker going from America to Europe.

The jet stream forms between warm air from the tropics hitting cold air from the Arctic. This clash brews storms in the Atlantic and drives them towards Europe, and because the jet stream wobbles its track can make huge differences to the weather: a jet stream to the north of Britain in summer often leaves us bathed in warm air from the south; if it passes over us it often brings wet weather; and a track to the south leaves us in the cold.

For much of this summer the jet stream has steered close to the north of Britain, then dived down in a big loop into the southeast of Europe. This has sent a barrage of depressions into northwest Britain, and then Romania, Bulgaria and Croatia, with deluges of rain that have benighted the region almost all summer, since June.

Wet weather for Britain and much of Europe is not that unusual at the end of summer. From August 20-30 there is often an outbreak of depressions as the jet stream picks up speed with the first hint of autumn cold in Greenland and the rest of the Arctic.

The unusual thing this year is how persistent the track of the jet stream has been in its sweep around Europe, locking high pressure over southwest Europe where it has created such an intense drought in Spain and Portugal since November. Unless the jet stream changes track, the outlook for Europe will be for similar conditions, for a few days or even several months.

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