Digitisation and Homogenisation of Swiss Climate Data (DigiHom)

Füllemann Christine*, Begert Michael*, Brönnimann Stefan**, Croci-Maspoli Mischa*
*Swiss Federal Office of Meteorology and Climatology MeteoSwiss, Krähbühlstrasse 58, CH-8044 Zurich (christine.fuellemann@meteoswiss.ch)
** Swiss Federal Institute of Technology, Institute for Atmospheric and Climate Science, Universitätstrasse 16, CH-8092 Zurich

The term DigiHom combines the intentions at MeteoSwiss i) to digitize long-term surface time-series from historical paper data and ii) to homogenize the complete data series with respect to make accurate estimates of the dimension of climate change and the corresponding effects. The goal of DigiHom is to make an important contribution to the national and international climate observation system by means of long-term climate series of Switzerland.
DigiHom has a time-frame from 2008-2011 and is accomplished in close collaboration with ETH Zurich. The homogenization process will be carried out at MeteoSwiss using a well established homogenization procedure (THOMAS, Tool for Homogenization of monthly data series, cf. Begert et al. 2005).
The surface observation stations processed within DigiHom are the long–term climate series of the newly defined Swiss National Basic Climatological Network (Swiss NBCN). This network defines the most valuable climatological stations in Switzerland and accordingly guarantees a long-term perspective of their operation. The Swiss NBCN consists of 28 climatological stations (different parameters), presented in Begert et al. (2007) and 46 precipitations stations (Begert, 2008) covering respectively all climatological regions of Switzerland. Representative climatological regions for the different surface observation stations have been calculated using the complete-linkage cluster analysis.
After the successful completion of DigiHom in 2010 the following climatological variables will be available electronically and in high-quality back to the year of their origin (most of them before 1900): temperature (mean, minimum, aximum), precipitation and sunshine duration. Although the coverage of stations at different altitudes is quite good, stations with multivariate time series are mainly located below 1000m asl. Higher elevated stations generally offer mean temperature and precipitation series. NBCN stations have all parameters starting before 1901. In this study the technical background to accomplish DigiHom will be presented and first results of homogenized long-term time-series will be introduced.

REFERENCES
Begert M., Schlegel T., Kirchhofer W. 2005: Homogeneous temperature and precipitation series of Switzerland from 1864 to 2000. Int. J. Climatol. 25, 65-80.
Begert, M., Seiz, G., Foppa, N., Schlegel, T., Appenzeller, C., Müller, G. 2007: Die Überführung der klimatologischen
Referenzstationen der Schweiz in das Swiss National Climatologial Network (Swiss NBCN), Arbeitsberichte der
MeteoSchweiz, 215, 43p.
Begert, M. 2008: Repräsentativität der Stationen im Swiss National Basic Climatological Network. Arbeitsberichte der
MeteoSchweiz, 217, 40p.
Brönnimann, S., Annis, J., Dann, W., Ewen, T., Grant, A. N., Griesser, T., Krähenmann, S., Mohr, C., Scherer M., Vogler C. 2006: A guide for digitising manuscript climate data. Climate of the Past, 2, 137-144.