TREVI, Italy — It was in June, the time of year when the first olives normally burst from their blossoms in the mild warmth of early summer, when Irene Guidobaldi walked through her groves in blistering heat and watched in horror as the flowers on her trees began to wither and fall.

The only way to save her family’s precious orchard in the hills of Umbria was to buy the most precious thing of all in this summer of drought: water.

Lots and lots of water.

And so, Ms. Guidobaldi, an eighth-generation olive grower, bought water by the truckload, nearly every day, for most of the summer.

The heat wave that swept across southern Europe this summer, which scientists say bore the fingerprints of human-induced climate change, is only the latest bout of strange weather to befall the makers of olive oil.