Scientists in Greece have developed a new method to predict when olive and oak trees will release allergy-triggering pollen into the air. This breakthrough could help allergy sufferers better prepare for the season and alleviate their symptoms.
The research, led by S. Papadogiannaki at the Aristotle University of Thessaloniki, focused on two trees common in the Mediterranean region—olive and oak. Their pollen is known to cause strong allergic reactions in many people, especially during spring.
Using data collected over several years in Thessaloniki, researchers found patterns in how and when these trees release their pollen. They used weather information and advanced computer models to predict the start, peak, and end of the pollen season. These predictions are important for helping doctors advise patients and for planning public health alerts.
Allergies on the rise as pollen seasons grow longer
In cities across Europe, up to 40% of people suffer from pollen allergies. Children are especially at risk. Pollen can cause sneezing, itchy eyes, and even asthma attacks.
The problem is worsening with climate change. Warmer weather means longer and more intense pollen seasons. That’s why being able to predict these seasons has become urgent.
Olive and oak trees are two of the biggest pollen producers in the region. In Greece, olive trees are widely grown, especially near Thessaloniki and the surrounding countryside.
Oak trees are common in the nearby mountains. Both are strong contributors to airborne pollen, which travels through the air and enters homes, schools, and workplaces.
Pollen traps and weather models reveal timing patterns
The research team studied pollen levels from 2016 to 2022 using data from a rooftop pollen station at Aristotle University, which has been operating since 1987. The station collects daily samples of pollen floating in the air.
By combining this data with weather records—such as temperatures, rainfall, and sunlight hours—the scientists developed models to forecast when pollen levels will rise. These models examine two main factors: the amount of cold required in winter to awaken the trees from dormancy, and the warmth needed in spring to trigger flowering.
They used several different methods to track this. One model counted the number of cold hours during winter. Another looked at how much heat built up as spring arrived. They also tested models that combined heat with the number of daylight hours.
Among all the methods tested, the most accurate predictions came from using a mix of cold-hour and heat-based models, supported by statistical tools that identify the most important weather conditions.
Pollen season timelines
Olive pollen season in Thessaloniki typically starts in early April and peaks in mid-May. On average, it lasts about 58 days. Oak pollen starts a bit earlier—usually in late March—and peaks around April 25. It also lasts about 55 days.
The models were able to predict these periods with good accuracy. However, some years were harder to predict, especially when weather conditions were unusual. For instance, in 2022, the olive pollen season lasted longer than usual, and the models failed to fully capture this change. Nonetheless, in most years, the predictions were close to reality.
The study also found that oak trees release more pollen than olive trees. Oak pollen levels were especially high in 2016, which had both an early start and a long season.
Compared to places like southern Spain, Thessaloniki had lower pollen counts overall, but the duration of the season was longer. This shows how local climate affects pollen behavior, even within the same region.
Temperature and rainfall matter
Researchers discovered that spring temperatures have the most significant impact on when olive trees release their pollen. For oak trees, winter temperatures and April rainfall were more important. This information helps explain why the pollen season can change from year to year.
If winter is too warm, trees may not get the cold rest they need. If spring arrives early, flowering might start sooner. But if spring is dry or unusually cool, flowering may be delayed.
Understanding these patterns enables scientists to predict not only when the season will start but also when it will end and how intense it will be.
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