Dry winters heat European summers

When southern Europe receives scant rainfall in the winter, the whole continent tends to bake the following summer.

Each of Europe’s 10 warmest summers between 1948 and 2005 followed a winter in which the continent’s Mediterranean countries experienced significant deficits in rainfall, says Robert Vautard, a climate scientist at the French National Center for Scientific Research in Gif sur Yvette. For those years, moreover, the scarcer the wintertime rainfall, the hotter the following summer, he notes.

Vautard and his colleagues turned to climate simulations to investigate the theoretical effect of wintertime droughts at latitudes below 46°N, an east-west line that runs just north of Venice and splits France in half. When portions of Europe south of that latitude began the summer with a soil-moisture content of only 15 percent, average July temperatures there would be as much as 6°C higher than if the soil had a more typical 30 percent moisture.

Also, some regions north of 46°N, such as Switzerland and southern Germany, would experience average July temperatures up to 2°C higher after a dry winter than after a wet one, even if the previous winter’s drought had been confined to southern Europe, the researchers note in the April 16 Geophysical Research Letters.

Because many climate projections suggest that southern Europe will become drier in the coming decades, the new findings suggest that European heat waves will become more frequent.

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