A team from the Swiss Federal Research Institute said that in Périgord and in Spain's Aragon region the amount harvested fell at around the same pace from 1970 to 2006, and this trend was in line with an overall decline in summer rainfall.
When they looked at harvests in northern Italy's Piedmont and Umbria they were also on decline, but not as badly as in France and Spain, and this correlated with relatively higher levels of summer rain in those regions.
The scientists believe questions hang over the future of the Périgord black truffle.
"Considering a variety of climate models, the researches predict incessant Mediterranean summer drying until the end of the 21st century, associated with a continuation of fading Spanish, French and Italian truffle harvests," they said.
Related: Get set for Lalbenque truffle market
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