Climate change is already threatening more than a quarter of Switzerland’s farmland with frequent and lengthy water shortages, according to official research.

The Swiss federal agricultural research station Agroscope said about 10 times more land would need to be irrigated to avoid lost harvests, some 400,000 hectares instead of the 38,000 hectares that currently receive regular irrigation.

But researcher Jurg Fuhrer said that such huge irrigation to cope with more frequent drought might not be economically viable or feasible.

Twenty-six per cent of usable agricultural land and 41 per cent of arable land is at risk due to the drier climate that has been emerging in recent years, the scientific study found.

The conclusions were based on a range of research including detailed observations of local climate, hydrological data and crop patterns between 1980 and 2006.

It showed that the Alpine country’s prime arable land, spread across lower lying northern plains and valleys, had been the hardest hit by a growing frequency of summertime drought, including the Rhine valley.

“I was surprised to see the size of the area,” said Mr Fuhrer. “The area is expanding, that’s the significant part.”

Swiss farmers should expect a period of damaging drought at least once every three years, the researchers predicted.

The Rhine is one of Europe’s biggest rivers, flowing northwards through Germany from its source in the Swiss Alps. The Rhone valley in southwestern Switzerland, which stretches into southern France, is also at risk.

“There are implications for anybody who lives along these rivers,” Mr Fuhrer pointed out.

Climate research cited by Agroscope has indicated that summer rainfall in Switzerland could be cut by up to a fifth by 2050.