Changes in birch and tree pollen seasonal patterns due to climate change

Abstract Climate change is clearly evident in Germany. Yet what changes does a 1 °C increase in the annual average maximum temperature bring about in the natural environment, for example? Pollen serves as an excellent bioindicator for determining these changes. However, since pollen counts are subject to natural fluctuations, long time series are required to detect effects such as those caused by climate change. Studies in other European countries demonstrated an earlier onset of the pollen season for nearly all pollen types and found that pollen levels have increased. In Germany, data for birch pollen, for example, are currently limited. In Bavaria, an automated pollen monitoring network was established in 2019, running in parallel with existing manual monitors. For Bavaria, it is evident that pollen is appearing progressively earlier in terms of start, end, and peak dates. Compared to start dates over the past 30 years, the birch pollen season now begins approximately 1 month earlier. The amount of birch pollen has also increased in recent decades. For hazel and alder, the manual system—which has the longest data series—does not collect data in winter, resulting in gaps in pollen dispersal data and making it more difficult to detect changes. However, indicator parameters such as hazel pollen in December (normally in February) show the same pattern as for birch. In the future, however, birch pollen levels in Bavaria will decline as tree populations shrink due to climate change. Similar trends are expected for the rest of Germany. For most people with pollen allergies, daily pollen levels—which are subject to significant natural variability—are more important than long-term trends. The new automatic pollen monitors with data available online display current pollen levels (e.g., Pollenscience.eu). Although the automatic network is not yet distributed evenly across Germany, the German Weather Service is currently expanding the network and expects to complete this by 2027.