Abstract:This paper describes the HISTALP database, consisting of monthly homogenised records of temperature, pressure, precipitation, sunshine and cloudiness for the 'Greater Alpine Region' (GAR,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(43)(44)(45)(46)(47)(48)(49). The longest temperature and air pressure series extend back to 1760, precipitation to 1800, cloudiness to the 1840s and sunshine to the 1880s. A systematic QC procedure has been applied to the series and a high number of inhomogeneities (more than 2500) and outliers (more than 5000) have been detected and removed. The 557 HISTALP series are kept in different data modes: original and homogenised, gap-filled and outlier corrected station mode series, grid-1 series (anomaly fields at 1°× 1°, lat × long) and Coarse Resolution Subregional (CRS) mean series according to an EOF-based regionalisation. The leading climate variability features within the GAR are discussed through selected examples and a concluding linear trend analysis for 100, 50 and 25-year subperiods for the four horizontal and two altitudinal CRSs. Among the key findings of the trend analysis is the parallel centennial decrease/increase of both temperature and air pressure in the 19th/20th century. The 20th century increase (+1.2°C/+1.1 hPa for annual GAR-means) evolved stepwise with a first peak near 1950 and the second increase (1.3°C/0.6hPa per 25 years) starting in the 1970s. Centennial and decadal scale temperature trends were identical for all subregions. Air pressure, sunshine and cloudiness show significant differences between low versus high elevations. A long-term increase of the high-elevation series relative to the low-elevation series is given for sunshine and air pressure. Of special interest is the exceptional high correlation near 0.9 between the series on mean temperature and air pressure difference (high-minus low-elevation). This, further developed via some atmospheric statics and thermodynamics, allows the creation of 'barometric temperature series' without use of the measures of temperature. They support the measured temperature trends in the region. Precipitation shows the most significant regional and seasonal differences with, e.g., remarkable opposite 20th century evolution for NW (9% increase) versus SE (9% decrease). Other long-and short-term features are discussed and indicate the promising potential of the new database for further analyses and applications.

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This paper presents an attempt to obtain high-quality data series of monthly air temperature for Slovenian stations network in the period from 1961 to 2011. Intensive quality control procedure was applied to mean, maximum and minimum air temperature datasets from the Slovenian Environment Agency. Recently developed semi-automatic homogenization tool HOMER (HOMogenisation softwarE in R) was used to homogenize the selected high-quality datasets. To estimate the reliability of homogenized datasets, three to six experts independently homogenized the same datasets or their subsets. Different homogenization parameter settings were used by each of the experts, thus comprising ensemble homogenization experiment. Resulting datasets were compared by break statistics, root-mean-squared-difference (RMSD) of monthly and annual values, and RMSD of the long-term trend. This semi-automatic homogenization approach based on metadata gave more reliable homogenization results than a fully automatic approach without metadata. While the network-wide linear trend of the dataset did not change after semi-automatic homogenization was applied, the distribution of the trends of individual stations became spatially more uniform. The arithmetic mean of the homogenized datasets of three experts was assigned as a reference homogenized dataset and it was compared with some publicly available homogenized datasets. The calculated linear trend on an annual level for Slovenia is strongly positive in all datasets, though the trend values are significantly different between the datasets. We conclude that the warming trend of near-surface air temperature in Slovenia in 1961-2011 is significant and unequivocal in all seasons, except for autumn. Mean, maximum and minimum temperature series indicate linear trend of around 0.3-0.4 ∘ C decade -1 on an annual level.

In the study, the climate regions of Slovenia were determined. The regionalization was based on the gridded climate data for the reference period 1981–2010. The climatic regionalization was performed predominately objectively with a combination of two statistical methods; the factor analysis which was followed by k‐means clustering. With the use of factor analysis the initial number of 31 climate variables was reduced to four variables or factors, which comprised the input for the cluster analysis where Slovenia was divided into six climate regions: Submediterranean climate region, Wet climate of hilly region, Moderate climate of hilly region, Subcontinental climate region, Subalpine climate region and Alpine climate region. Compared to previous climatic regionalization studies for Slovenia, the presented study uses a higher degree of objectivity in the determination of the extent and borders between climate regions. The current study was based purely on climate data, while in the previous studies, the borders were defined more subjectively, based on the authors' expertise of local climate.