Annual and seasonal variability of precipitation and temperatures in Slovenia from 1961 to 2011

Abstract

Spatial and temporal variability of annual and seasonal (summer and winter) precipitation sums and mean temperatures observed at forty-six stations in Slovenia from 1961 to 2011 were analysed. Principal component analysis (PCA) and a varimax rotation with Kaiser normalization were used to determine the dominant precipitation and temperature patterns in Slovenia. Time series data from the PCA (the principal components, PCs) were used to look for the existence of linear trends and periodicity in the precipitation and temperature data using the Mann-Kendall test and spectral analysis. The relationships between the PCs and circulation patterns, such as the North Atlantic Oscillation (NAO), the East Atlantic (EA) pattern, and the East Atlantic/West Russia (EA/WR) pattern, were also examined. The first four PCs of precipitation (temperature) contributed from 78.7% in summer to 94.5% in winter (98.4% in winter to 98.5% in summer) of the total variance, and their loadings indicated that the most (least) intensive signal was observed over mountainous northwest Slovenia. A statistically significant decrease of PC1 in annual precipitation and increase in mean annual and both seasonal temperatures was found. Significant relationships existed between annual and winter precipitation in Slovenia and the NAO, and temperature and the East Atlantic pattern from 1961 to 2011. Applying the spectral analysis, periods of 2.4 years in summer precipitation and 2.8 years in winter precipitation series, and 2.1 years in annual temperature (significant at the 5% level of significance) were found in Slovenia.