Climate Extremes Threaten Mediterranean Olive Harvests More than Rising Temperatures

“An olive grove can survive a warmer average climate,” Italian agroclimatologist Marco Moriondo told Olive Oil Times. “But a single day of extreme heat during flowering can destroy an entire harvest, even if the rest of the season is perfect.”

Moriondo’s observation comes on the heels of the latest European State of the Climate 2025 report released by the European Union’s Copernicus program and the World Meteorological Organization. The report described 2025 as one of the driest years on record for soil moisture in parts of southern Europe, while extreme weather events intensified across the Mediterranean basin.

In May 2025, scientists found that 35 percent of Europe was affected by extreme agricultural drought, adding to previous drought conditions caused by prolonged soil moisture deficits, with consequences for crop yields and wildfire risk.

Besides confirming that surface temperatures in Europe continue to rise faster than in most other regions of the world, the report also highlighted how increasingly frequent heatwaves, prolonged dry spells and concentrated rainfall events have major implications for olive oil production across the Mediterranean.

“We talk about temperatures increasing by one degree, one-and-a-half degrees or two degrees. But what comes with that are extreme events, both drought-related and thermal, which in some cases are more important than the average climate itself,” Moriondo said.

A researcher at Italy’s National Research Council specializing in climate impacts on Mediterranean agriculture, Moriondo said that discussions about farming have historically focused on gradual shifts in annual temperatures and rainfall totals. But those averages can obscure the more damaging effects of short-term extremes.

According to Moriondo, olive trees are especially vulnerable during flowering and pollination, when excessive heat can sterilize pollen, dry flowers or prevent successful fruit set.

Researchers have already identified temperature thresholds beyond which physiological processes begin to fail in olives, grapevines and wheat. “The heatwave is no longer exceptional,” Moriondo said. “Now we expect it and we expect it to last.”

The problem is compounded by changing rainfall patterns across the Mediterranean basin. Moriondo noted that annual precipitation totals alone no longer provide an accurate picture of agricultural water availability.

“The same amount of rain falls in fewer days,” he said. “That water is often lost because the soil cannot absorb it properly.”

As a crop adapted to the slow seasonal rhythm of Mediterranean moisture, the olive tree may experience severe physical and metabolic stress following a sudden deluge of extreme rainfall.

Fast-moving torrents on vulnerable slopes can strip away fertile topsoil and expose roots. Waterlogged soils may also sharply reduce oxygen levels around the roots, triggering root asphyxiation and damaging fine absorbing root hairs.

Such stress can lead to leaf yellowing and fruit drop weeks after the rainfall event. The humid conditions created after intense storms may also favor outbreaks of Peacock Spot and root rot, especially in groves with bare or heavily tilled soils.

Moriondo noted that orchards managed with permanent ground cover often prove more resilient than bare soils, which are more exposed to erosion and long-term degradation.

The Copernicus and WMO report confirmed a pattern of longer dry intervals interrupted by increasingly intense precipitation events. For agriculture, longer periods of water stress combined with greater runoff can reduce effective groundwater recharge and accelerate soil erosion.

“That is the aspect that worries me most,” Moriondo said. “Not simply that rainfall decreases by ten percent, because perhaps many could adapt through irrigation. The real problem is that much of the rain may arrive in concentrated events and be effectively lost.”

Growers across southern Europe are also reporting increasingly irregular flowering patterns and unstable production cycles. Many producers describe olive trees continuing vegetative activity well into winter due to milder temperatures, disrupting dormancy patterns that have historically regulated the tree’s annual cycle.

Moriondo said he has observed the phenomenon personally in Tuscany.

“In the past, shoots would stop developing in autumn,” he said. “Now I often still see green shoots deep into winter. The tree may not complete its chilling requirements properly, the accumulation of cold hours needed to regulate flowering and dormancy. That creates delays and irregular flowering patterns.”

Such conditions may also increase vulnerability to late frosts, which can damage tissues that remain metabolically active during unusually mild winters.

Although some modeling studies suggest that most Mediterranean cultivars may remain within safe chilling thresholds for the foreseeable future, researchers increasingly warn that year-to-year variability could still create severe disruptions.

Climate instability may also be amplifying one of the olive tree’s defining physiological tendencies: alternate bearing. Producers in Italy, Spain and other Mediterranean countries increasingly report abundant harvests followed by sharp production declines the following year.

“If an extreme event destroys production in one year, then that imbalance can trigger a strong rebound the following season,” Moriondo said.

Recent modeling studies suggest those fluctuations could become more pronounced under future climate conditions. One study projected yield declines of up to 28 percent in parts of the Iberian Peninsula, accompanied by a 20 percent increase in interannual variability.

Across the Mediterranean, many growers are already expanding irrigation systems and adopting more intensive orchard management strategies. But Moriondo warned that future water availability itself may become one of the sector’s primary constraints.

Studies indicate that irrigation demand for olive orchards could rise between 5 and 27 percent under future climate scenarios, increasing competition among agriculture, urban systems, industry and ecosystems for limited water resources.

“It will not be easy everywhere to provide the amount of irrigation required,” Moriondo said. “The necessary water may conflict with other uses.”

The challenge appears especially significant for traditional rainfed orchards, which many researchers consider among the most vulnerable systems under future Mediterranean climate conditions.

Even so, Moriondo said the future of Mediterranean olive cultivation should not be viewed in apocalyptic terms. Olive trees remain highly resilient crops, capable of adapting to drought and poor soils better than many other agricultural species.

The impact of climate change on olive oil quality, however, remains more difficult to estimate. While scientists can increasingly model impacts on yields and water use, understanding how heat stress, drought and shifting seasonal patterns affect olive oil composition is far more complex.

“Producers are increasingly concerned about quality,” Moriondo said. “That is one of the aspects that still needs much more investigation.”