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Kick-off for the European pollen season

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For many people allergic to pollen, timing the start of medication is crucial. You want to begin medication well before the onset of a new pollen season, in order to for the medication to take effect. On the other hand, medication has side-effects (like making you drowsy), so you do not want to start the medication before it is necessary. Hence, a common request from our readers is to receive an advance warning, e.g. ten days prior, to when a new pollen season is about to start.

Throughout this spring, Airmine will post updated reports on how the pollen season develops throughout Europe. Although we do not yet have a rigorous model in place to predict future pollen levels, we will explore whether it is possible to predict the onset of a new pollen season from how the “onset front” is moving from south to north.

The “pollen front”

Alder (alnus) and hazel (corylus) normally kick off the pollen season in Europe. The forests on the Hungarian-Austrian border are typically very early pollen starters and see relatively high pollen levels in early January. The pollen season then successively follows westwards and northwards in what we call the “pollen front”.

The map below illustrates the phenomena. It shows prevalence of alder pollen (faded green colour) and typical pollen levels for alder January 7th (bright green and orange colours). We can clearly see the Hungarian-Austrian forests stand out.

Early January averages: Prevalence and normal pollen levels for alder on January 7th (averages based on data from last 10-15 years).
Hazel normally follows the same pattern, except that pollen levels are lower in Portugal and higher in Central Italy.

Currently (January 2) almost none of the monitoring stations in Europe detect significant levels of alder or hazel pollen, but this is expected to change over the next 2-3 weeks. As can be seen from the map below, which shows historic averages, by late January the season for alder has normally kicked off in large parts of Europe. For example in France, there will usually be high levels of pollen from alder and hazel by late January.

Late January averages: Normal pollen levels for alder in late January (averages based on data from last 10-15 years).
Hazel follows more or less the same pattern but tends to have even higher levels in the hotspots, for example close to Clermont-Ferrand in France.

Will 2020 be a normal year?

Based on assessment of alder catkins, the university in Vienna estimates that alder will be ready to blossom in the middle of January (January 13th in Vienna). The exact date for the pollen onset will depend on the outdoor temperature, but this means that the Austrian forecasts are more or less on track with what has been seen historically.

The pollen count in the Netherlands, however, indicates a significant deviation from the historic trends. Here the pollen counts for alder in late December has been significantly higher than the historic pattern, see the figure below. Normally, by January the pollen count in the Netherlands tend to flatten out and decrease due to relatively cold weather. But the weather forecast for the next ten days is five degrees above the average for January so it might look like the alder pollen season has already start for earnest in the Netherlands, one month earlier than normal.

Count of alder pollen in the Netherlands December 2019, compared to the historic average.

Is this likely to mean that the pollen season will start earlier than normal in other countries in Europe as well? Not necessarily, the monitoring stations in France and Germany has counted no alder pollen in December. In Belgium, alder already have catkins, but the pollen season is not expected to start before sometime into January. Hence, insofar the high pollen levels in the Netherlands seem to be a relatively local phenomenon, but indicate an early start in the neighbouring areas.

So when does it come? Estimated start of alder and hazel pollen season 2020

The currently available data indicates that the onset for pollen from alder and hazel will develop as follows in Europe:

Onset within 1 week (January 9th), or already started

  • Warm forests in Austria-Hungary
  • Amsterdam, Brussels, Düsseldorf
  • Rome
  • Northern Portugal

Onset within 2 weeks (January 16th)

  • Vienna
  • Scotland
  • Lower parts of the Alps (France, Italy, Switzerland, Austria)
  • Corsica, Sardinia

Onset within 3 weeks (January 23rd)

  • Most of Europe, except Norway, Finland, Sweden (north of Gothenburg), the Baltic, Belarus, Ukraine

Onset within 6 weeks (February 13)

  • Norway, Belarus

Note: The estimated dates are based on historical data and weather forecasts and contain uncertainties. There may be major local variations, based on weather and growing conditions.

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