Prispevek podaja način statističnih obdelav pretokov izvirov Vipave z namenom vpogleda v značilnosti odtoka na območju kraško razpoklinskih vodonosnikov. Statistične analize temeljijo na izračunu sekvenčnih trendov letnih decilnih vrednosti 45 letnega niza hidroloških opazovanj med leti 1960 in 2004. Za izvire Vipave so značilna krajša trajanja visokih in daljša obdobja srednjih in nizkih voda. Razmerje med nizkimi, srednjimi in visokimi pretoki znaša približno 1:10:100. Večina vode proti izvirom odteka iz neposrednega padavinskega prispevnega zaledja izvirov. Da bi zmanjšali napako zaradi subjektivnosti rezultatov, je bil izračun sekvenčnih trendov izveden komplementarno po dveh različnih metodah in sicer po metodi umerjenih delnih vsot (RAPS) in z neparametrično analizo sekvenčnih trendov po metodi Mann Kendall. Z metodama smo določili pod-obdobja znotraj posameznih časovnih vrst, nato pa smo na podlagi rezultatov ugotavljali podobnosti med posameznimi časovnimi vrstami, ki so jih predstavljale letne decilne vrednosti pretokov izvirov Vipave. Analize sekvenčnih trendov so potrdile podobnosti med nekaterimi decilnimi vrednostmi, saj so bile dolžine in smeri trendov pod-obdobij podobni med nizkimi, srednjimi in visokimi decilnimi vrednostmi pretokov. Ključne besede: kraški izviri Vipave, sekvenčni trendi, umerjene delne vsote, neparametrični sekvenčni Mann Kendall test, primerjava decilov.

Systematic hydrologic monitoring of groundwater quantity at the national level in Slovenia has been ongoing since 1952. An insight into long-term groundwater level data enables us to delineate parts of aquifers with similar groundwater level oscillation properties as well as to identify changes of those properties in time. We used variety of statistical methods to identify long-term behaviour of groundwater level oscillation of groundwater body (GWB) Murska kotlina. Results showed that fluctuation of groundwater level in time reflect complex set of events that originate in natural or anthropogenic interferences. Using percentile analysis in combination with cluster analysis, we were able to isolate areas with a related groundwater fluctuation. Results of long-term data trends analyses of monthly groundwater level showed the impact of the research area climate on long-term and seasonal groundwater level fluctuation. In addition to natural causes, by performing trend analysis on groundwater level data, we were able identify some human induced interventions into the environment made in the past.

<p>River water represents the spatial and temporal integrator of the isotopic composition of precipitation in a catchment area. Stable isotope measurements of oxygen and hydrogen (<em>δ</em><sup>18</sup>O and <em>δ</em><sup>2</sup>H) in stream waters and precipitation are widely applied to investigate hydrological pathways and transit times. In this study, we apply the stable isotope approach to improve knowledge on the hydrological characteristics of the River Sava, Slovenia, by performing monthly sampling of river water at two locations: Brod and Šentjakob and precipitation at one location (Ljubljana–Reactor), between 2020 and 2021. Gathered data was used for preliminary estimations of water transit times in streamflow. Moreover, different methods were used to determine the Local Meteoric Water Line and comparison with precipitation data for the period 1981–2021 to estimate temporal changes and transit times of the River Sava at selected locations.</p><p>The climatic characteristics of the investigated area are also reflected in <em>δ</em><sup>18</sup>O and <em>δ</em><sup>2</sup>H of precipitation that has been monitored since 1981. The <em>δ</em><sup>18</sup>O and <em>δ</em><sup>2</sup>H values of precipitation reveal strong seasonal variations, while the tracer output signal in the River Sava is dampened. Site-specific long-term (1981–2021) covariation of <em>δ</em><sup>18</sup>O and <em>δ</em><sup>2</sup>H is also in good agreement with Global Meteoric Water Line (GMWL), while short-period lines (2020–2021) differ in slope and intercept but lie close to the line GMWL. A longer time series is more suitable for the determination of the LMWL, as the error is much higher for shorter two-year periods. </p><p>The exponential flow model produced mean stream water transit times of 4.2 and 3.1 years at Sava Brod and Sava Šentjakob, respectively, whereas estimated transit times were longer compared to the results of previous investigations. Although the identified results are hydrologically plausible, the limitation of this and previous studies are presented as uncertainties resulting from a short sampling period and low sampling frequencies.</p>