Long Swiss meteorological series

Ensuring long-term climate records is one of the core tasks of GCOS. Apart from maintaining high-quality stations for future needs, extending the series back in time using data rescue (followed by quality control and homogenisation) is a key aim. This proposal responds to the Pillar 1, priority 1.4 of GCOS Switzerland (extend time series in the past through promoting data rescue) and addresses the generation of long meteorological series. Switzerland features two long temperature time series reaching back into the mid-18th century (Basel and Geneva) as well as a third, 200-yr long series from Gr. St. Bernhard. These series are widely used to put present climatic changes into a long-term context (e.g., in the CH2018 Technical Report). However, prior to 1864 the series from Basel and Geneva are largely built on daily data produced and assessed in the 1950s and 1960s. Also, both are infilled (Geneva with data from Neuchâtel, Basel with data from Mulhouse and Delémont, respectively). In the MeteoSwiss-funded project DIGIHOM III we digitised the original (sub-daily, all variables) data underlying all three series (though Geneva only back to 1798). In the ongoing SNF project CHIMES (Swiss Early Instrumental Measurements for Studying Decadal Climate Variability) we discovered a large number of additional series for Basel and Geneva that (a) could fill the gaps and (b) provide many overlaps and thus opportunities to better quality check the series.

Furthermore, we discovered a large number of series from Zurich, which potentially allow constructing meteorological series back to 1718 (though with a gap) or back to the 1750s. This would constitute a third long Swiss climate series (potentially even the longest, if the very early data prove useful and if the gap can be filled). A minor backward extension of the Gr. St. Bernhard series by two additional years will also be conducted. Most of the original data sheets have already been imaged by us and a considerable fraction has been digitised. In this project we propose to digitise all remaining series found for the three locations. With the additional series and more overlap, a better quality can likely be achieved. Once the data have been digitised, we will perform Quality Control on all series and, depending on the results, include the temperature series for a new merge, followed by homogenisation. Quality control will also be performed for pressure and (where available) precipitation. As the quality of the series to be digitised is not yet known, we cannot guarantee that three new high-quality climate series will emerge. However, in any case we will provide additional information for assessing Swiss preindustrial climate and its variability. The series from Zurich is an entirely new series that is of interest for Swiss climate assessments and research.

Project team:

Dr. Yuri Brugnara, Prof. Dr. Stefan Brönnimann

Funding:

Federal Office of Meteorology and Climatology MeteoSwiss in the framework of GCOS Switzerland

Project duration:

September 2019 – August 2021