Phenology and pollen

As a consequence of rising temperatures, the vegetation develops significantly earlier these days during spring and summer than several decades ago. Likewise, the pollen season of plants that cause allergies starts earlier. Therefore, plants are excellent indicators for the effect of the global rise in temperature. The weather service MeteoSwiss is collecting a variety of data to illustrate these changes.

Opening image: Blooming hazel bush


Phenology is the study of cyclic growth and development phenomena occurring over the course of a year, especially in relation to flora. The start times (date) of the so-called phenophases such as new leaf formation, flowering, ripening of fruit, changing colour and falling of leaves are observed and recorded in plant phenology.

Reports about the current vegetation development

The phenological observation network of Switzerland has been in place since 1951. Presently, 26 plant species are observed at nearly 160 stations. These observations represent the basis for the climatological evaluation of the current vegetation development as it is described in the monthly climate bulletin and in the climate report. The current analyses can be retrieved under climate reports.

The spring index

The spring index shows the point of time of vegetation development in spring compared to the long-time average from 1981-2010. The annually determined index summarises the phenological spring phases, from the blooming of the hazel bush to the new leaf formation of the beech tree.

Additional phenological series of observations

Aside from the observation network, two long-term and hence very valuable phenological series of observations exist in Switzerland, which have been used to observe two types of plants since 1808 and 1894 at the same location: a horse chestnut tree in Geneva and the blooming of a cherry tree in Liestal.


The extent of pollen dispersal changes year of year, and the start of blooming, especially of tree pollen, varies greatly, depending on the temperatures in the weeks and months prior. In addition to the weather development, pollen dispersal is affected by climate and is hence an important climate indicator.

Reports and graphic charts of the current pollen season

Long-time monitoring of pollen data reveals changes in pollen dispersal: an advancement or delay, intensification or weakening of the pollen season or the emergence of new allergenic pollen types such as for example ragweed. The weather service MeteoSwiss is measuring and analysing the pollen dispersal. The current pollen season is described in comparison with the average in the seasonal climate bulletin and in the climate report, both of which can be retrieved under climate reports. The ongoing pollen season as well as the comparison with the long-time average are also evaluated graphically.

The weather service MeteoSwiss had been compiling annual reports of the pollen dispersal until 2013. Starting from 2014, these evaluations will regularly be incorporated into the reports mentioned above.

Further information