Open Geosci. 2016; 8:593–605 Research Article Open Access Dragan D. Milošević*, Stevan M. Savić, Milana Pantelić, Uglješa Stankov, Igor Žiberna, Dragan Dolinaj, and Igor Leščešen Variability of seasonal and annual precipitation in Slovenia and its correlation with large-scale atmospheric circulation DOI 10.1515/geo-2016-0041 1 Introduction Received April 3, 2015; accepted December 17, 2015 Abstract: This paper examines temporal and spatial vari- Precipitation is a very important meteorological element ability and trends of annual and seasonal precipitation in in the Mediterranean region (MR) as its future change can Slovenia and their relationship with three atmospheric cir- impact human activities (e.g. water management, agricul- culation patterns represented by their indices: North At- ture) and ecosystems. Significant progress has been made lantic Oscillation index (NAOi), Mediterranean Oscillation on climate projections for the MR [1]. Future projections re- index (MOi) and Western Mediterranean Oscillation index garding seasonal precipitation show predominant reduc- (WeMOi). Data from 45 precipitation stations were used tions for spring, summer and autumn, however projec- for the period 1963–2012. Mean annual precipitation varies tions for winter are distinctly different [2]. Precipitation is from 736 mm in eastern Slovenia to 2,518 mm in north- projected to decrease in all parts and all seasons (the most western Slovenia. A significant annual precipitation de- significant percent change occurs in summer) except for crease (from −3% to −6% per decade) is observed in west- the northernmost parts in winter [3]. This is in accordance ern Slovenia. Significant negative trends are observed in with the expected drying over the MR as a part of global southwestern Slovenia in summer (from −4% to −10% per warming [4]. decade) and near the Adriatic coast in spring (from −6% to Precipitation variability and trends in the MR have −10% per decade). Non-significant negative and positive been analyzed in many studies. For example, Ziv et al. [5] trends are observed in winter and autumn, respectively. analyzed changes in the precipitation regime of Israel Results indicate significant correlations between winter showing a statistically non-significant decreasing trend precipitation and MOi (from −0.3 to −0.7), NAOi (from prevailing in most of the country. The majority of Is- −0.3 to −0.6) and WeMOi (from 0.3 to 0.6). Significant We- rael has significant precipitation decrease only during MOi influence is observed in spring and autumn, while spring. Luković et al. [6] examined spatial patterns of rain- NAOi and MOi influence has not been detected. Annual fall trends in Serbia suggesting only weak, mostly non- precipitation and WeMOi are significantly correlated in significant trends. The study of de Luis et al. [7] has shown central and eastern Slovenia, while significant NAOi and a significant annual precipitation decrease in northwest- MOi influence is observed in western Slovenia (with the ern and western Slovenia and during all seasons, except larger area covered by MOi influence). autumn. As local changes in meteorological variables in mid- Keywords: precipitation; atmospheric circulation; North latitudes are mainly controlled by atmospheric circula- Atlantic Oscillation; Mediterranean Oscillation; Western tion [8, 9], the correlations between circulation indices Mediterranean Oscillation; Slovenia Uglješa Stankov: Center for Spatial Information of Vojvodina *Corresponding Author: Dragan D. Milošević: Climatology and Province, Faculty of Science, University of Novi Sad, Trg Dositeja Hydrology Research Centre, Faculty of Science, University of Novi Obradovia 3, 21000 Novi Sad, Serbia Sad; Trg Dositeja Obradovića 3, 21000 Novi Sad, Serbia, E-mail: Igor Žiberna: Department of Geography, Faculty of Arts, University [email protected] of Maribor, Koroška cesta 160, Maribor, Slovenia Stevan M. Savić, Milana Pantelić, Dragan Dolinaj: Climatology Igor Leščešen: Department of Geography, Tourism and Hotel Man- and Hydrology Research Centre, Faculty of Science, University of agement, Faculty of Science, University of Novi Sad; Trg Dositeja Novi Sad; Trg Dositeja Obradovića 3, 21000 Novi Sad, Serbia Obradovića 3, 21000 Novi Sad, Serbia © 2016 Dragan D. Milošević et al., published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License. 594 Ë Dragan D. Milošević et al. and precipitation in the MR are very important to analyze. The Republic of Slovenia is situated in the central- The relationships between atmospheric circulation pat- southern part of Europe (Figure 1) abutting four distinct tern indices and precipitation in Slovenia have not been geographical regions: the Mediterranean Sea, the Alps, the well identified: only a few studies [10, 11] have been made Dinaric Alps and the Pannonian Basin [22]. Slovenia ex- on this topic with only a limited number of precipitation tends between 45°25’ and 46°30’ N and 13°23’ and 16°36’ stations investigated. One of the goals in this paper is to an- E [23] and covers an area of 20,273 km2 [22] with a pop- alyze these relationships in order to obtain a better under- ulation of 2.06 million. The Alpine macroregion is in the standing of the causes of precipitation variability in Slove- north of Slovenia, while the Mediterranean macroregion nia. The study includes data on the large-scale North At- is in the west of Slovenia. Toward the east, the Mediter- lantic Oscillation (NAO) and regional Mediterranean and ranean macroregion is replaced by the Dinaric macrore- Western Mediterranean Oscillations (MO and WeMO, re- gion that stretches in a northwest-southeast direction and spectively) known to affect the MR. covers most of the southern part of Slovenia. The Pannon- NAO is associated with a meridional dipole structure ian macroregion is a densely populated and intensively in sea level pressure with two centers of action located cultivated area at the east end of Slovenia [24] (Figure 1). near Iceland and the Azores [12]. A positive NAO phase Submediterranean, temperate continental and alpine cli- leads to more intense precipitation over northern Europe, matic influences intertwine in the territory of Slovenia. whereas a negative NAO phase causes a precipitation shift However, most of Slovenia has a temperate continental towards southern Europe [8]. The influence of NAO on pre- climate. Alpine climate characterizes higher and lower cipitation in the MR has been investigated by a number of mountain areas to the north and west of the country, while authors [5, 8, 10–14]. A study by Sušelj and Bergant [11] a submediterranean climate is present in the south and showed significant negative correlation between NAOi and southwest of the country at the Adriatic coast (coastal sub- precipitation in Slovenia. However, this interpretation is mediterranean climate) and its hinterland (inland sub- limited by the fact that only four selected meteorological mediterranean climate). Continental climate intensifies stations represented the whole country which is geomor- with the distance increase from the Adriatic Sea and Alps- phologically and climatologically diverse. Dinaric mountain barrier towards the eastern and north- MO was defined in order to explain opposing atmo- eastern Slovenia [25]. spheric dynamics between the western and eastern part In the study of de Luis et al. [7] it was discussed that of the Mediterranean basin. The original MOi was defined changes in large-scale atmospheric circulation patterns as normalized pressure difference between Algiers and may have contributed to an observed long-term drying in Cairo [15]. A second version of this index, which was used Slovenia. This study contributes to the investigation of in this paper, can be calculated as the difference of stan- these suggested relationships. The main goals of this pa- dardized pressure anomalies at Gibraltar and the Israeli per are to investigate temporal and spatial variability and meteorological station of Lod [16]. The influence of MO trends of annual and seasonal precipitation in Slovenia on precipitation variability has been analyzed in numer- and to correlate them with indices of the large-scale (NAOi) ous studies [5, 10, 11, 13, 17–19]. A study of Sušelj and and regional (MOi and WeMOi) atmospheric circulation Bergant [11] showed significant negative correlation be- patterns, which are more representative for MR precipita- tween MOi and precipitation in Slovenia as registered at tion. four selected meteorological stations (Ljubljana, Murska Sobota, Rateče and Postojna). WeMO was defined by Martin-Vide and Lopez- 2 Data and methods Bustins [20] by means of the dipole composed by an an- ticyclone over the Azores and a depression over Liguria. Annual and seasonal precipitation in Slovenia recorded at This is the situation with a WeMO positive phase, while 45 stations was analyzed (Figure 1, Table 1). Selected pre- in the negative phase the situation is the opposite. We- cipitation stations are located on the territory of each of the MOi was defined as the result of the difference between different geographical regions of Slovenia: 16 in the Alpine standardized values in surface atmospheric pressure in macroregion, 15 in the Dinaric macroregion, 10 in the Pan- San Fernando (Spain) and Padua (Italy). WeMOi’s influ- nonian macroregion and 4 in the Mediterranean macrore- ence on climate variability in the Iberian Peninsula has gion. Selection of adequate stations