50-year time series of phenological phases in Germany and Slovakia: a statistical comparison
Bissolli, Peter; Müller-Westermeier, Gerhard; Dittmann, Ernst; Remisová, Viera; Braslavská, Olga; Stastný, Pavel
Within a bilateral project of the meteorological services in Germany and Slovakia, time series of phenological phases in both countries have been analysed and compared for the time period 1951-2000. Phases of plants from all seasons which are available in both countries have been selected for a sample of eight representative stations from the observation networks of the meteorological services. The investigation comprises trend analysis, comparison of medians of the phase onset date and its year-to-year variability, their changes between the subperiods 1951-1985 and 1986-2000 and correlation with monthly averaged air temperature near surface. Differences between the phase onset dates in Germany and Slovakia can be found especially for early spring, when the onset dates are sooner and the year-to-year variability is higher in Germany compared to Slovakia. Later on in the year, differences between maritime and more continental regions within Germany become more important than differences between the two countries. The trend analysis shows that trends to sooner onset dates in spring and summer for the period 1951-2000 can be detected in general clearly in Germany, while in Slovakia trends of different sign and weaker trends can more often be found. Since the correlation between phenological phases and temperature is strong in both countries and also certain patterns of variability appear in both countries, the variability of phenological phases reflects large-scale climate change and its impact on vegetation. A future international action on a European basis is suggested to create a phenological reference data set for the area of Europe, providing a data base for climate monitoring applications and climate change impact research.