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.