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, 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.

Some years, like this one, the heat comes early and stays. Other years, it rains so much — as it did in 2014 — that the olive fly breeds like crazy, leaving worms inside the olives. Or there’s an untimely frost when the fruits first form, which is what happened in Beatrice Contini Bonacossi’s groves in Tuscany. Or, an early hot spell is followed by a week of fog and rain, which is what happened on Sebastiano Salafia’s farm in Sicily a few years ago, leaving the trees confused, as he put it, about when to bear fruit.

“Every year, there’s something,” Salafia said.

Gone are the days when you could count on the mild “mezze stagioni,” or half-seasons, that olives rely on before and after the heat. Gone, too, is the cycle you could count on: one year good, next year not good.

Now, said Guidobaldi, stretching wide her long twiggy arms, “It’s like playing the lottery.”

Olive trees are hardy survivors. In the Bible, a dove brings an olive leaf to Noah on the ark, a sign that the world is not entirely destroyed. Olive oil is central to food and folklore across the Mediterranean. And its health benefits have been so extolled that global demand for extra-virgin olive oil has surged.

Now, a changing climate is turning olive oil into an increasingly risky business — at least in the Mediterranean, the land of its birth.

Harvests have been bad three of the last five years, subject to what Vito Martielli, an analyst with Rabobank, based in Utrecht, Netherlands, called weather-related “shocks.” And with growing demand, wholesale prices have gone up.

No one will go hungry if there’s not enough olive oil on the market. But the impact of climate change on such a hardy and high-end product is a measure of how global warming is beginning to challenge how we grow food.

The forecast for olive oil production this year is mixed. In Italy it’s expected to be 20 percent below the 2000-2010 average, though better than last year, according to the International Olive Council, with some growers expecting a smaller but very tasty yield. Spain, the world’s largest producer, expects at least a 10 percent dip from last year, according to the council; the Spanish growers association forecasts a much bigger dip. Greece is expected to have a robust harvest. So, too, Tunisia.

But as the supply from the Mediterranean becomes more unpredictable, some bottlers are looking elsewhere as future sources of oil. Even some champions of Mediterranean oil, like Nancy Harmon Jenkins, author of “Virgin Territory: Exploring the World of Olive Oil,” recommend venturing further afield.

“I hesitate to say this because I love the Mediterranean and I want people to have Mediterranean olive oil,” she said, “but I think California is going to be more and more important in the years ahead and places like Australia and New Zealand.”

Between June and August this year, it was exceptionally hot and dry across southern Europe. In Spain, temperatures soared above 105 degrees Fahrenheit (40 degrees Celsius) in July. In Italy, rainfall was 30 percent below normal levels — and in parts of the country, much lower still.

Scientists with the World Weather Attribution program, a group dedicated to the study of extreme weather, concluded last month that the “the chances of seeing a summer as hot as 2017” had increased tenfold since the early 1900s, and the chances of a heat wave like the one that hit the region for three days in August, nicknamed Lucifer, had risen by four times.

“We found a very clear global warming fossil fuel fingerprint,” said Heidi Cullen, a climatologist who heads the program.

Ask Italian olive growers about the weather this year and you hear a wide range of answers. It rained on one hill. It didn’t rain on the neighboring one. One olive variety made it through the heat; another didn’t. Even in one orchard, one tree hung heavy with fruit; another barely had any.

Many said they would have to invest in irrigation. The one upside of the heat, they all said, was that the olive fly withered, too.

On an unseasonably warm Monday in October, Contini Bonacossi and her brother, Filippo, took me through their family estate, known as Capezzana, in the hills northwest of Florence. Here and there, tiny, dried-up olives lay on the ground. A few trees were bare. But many were drooping with fruit: fat, purple-green olives, the sight of which made Filippo exceedingly happy.

“He is very excited,” Contini Bonacossi said of her brother. She was less so. Capezzana would produce 20 percent less oil this year; as Capezzana’s sales chief, she would have to ration it out to her loyal customers.

Guidobaldi, for her part, was taking no chances. She started harvesting in late September, the earliest ever on the estate. It was still scorching hot. What if a freakish storm came and knocked the olives down?

“Bellissimo,” she said, caressing the olives she had saved. “I don’t have children. These are my children. You can’t just ignore them one year and then come back the next year and everything is OK.”

On the southern edge of Tuscany, in a valley of scraggly oak, Riccardo Micheli didn’t have the luxury of saving his trees with water trucks.

Unlike Guidobaldi’s conventional farm, Micheli ran his, the Agricola Nuova Casenovole, according to biodynamic principles: he used no pesticides and left much of his land to wilderness.

This year, nature did not return the favor.

By June it was burning hot. The hills around his groves turned red, then brown, as though the seasons had forgotten themselves and June had turned into November.

His early-blooming Moraiolo olives, one of three varieties that go into his oil, held on to their branches. But the late-blooming leccio del corno, the variety that gives his oil a spicy, dark kick, burned on the branches and dropped. Soon his entire field of leccio del corno was carpeted with fallen flowers, like summer snow.

To water them, Micheli feared, could moisten the soil enough to invite the dreaded fly and then ruin everything.

This year, he expects to produce 60 percent less oil than normal. And because his oil won’t contain leccio del corno olives, it will be lighter than usual, less spicy and lower in the polyphenols that make olive oil healthier than other oils.

The dry heat, in other words, would alter how much oil he makes, but also its quality.

“For the future we don’t know what to do,” Micheli said. “One year, it’s too much rain. Other year, it’s too much heat. Next year, who knows?”

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