An improved scientific understanding of interactions between precipitation, surface and groundwater under the current and future climatic conditions is required to better comprehend the water cycle and manage water resources. In Alpine climate zone the storage of precipitation in snowpack, and the subsequent spring melting, both highly variable in space and time, substantially impacts the water cycle. Aquifers recover during snowmelt (IAEA, 2010). Therefore, it is challenging to incorporate snowmelt processes and delay in incorporation of water stored as snow cover into hydrological models.
Stable isotopes of oxygen and hydrogen have been used to study snow deposition and the subsequent alteration of snowpack characteristics and its influence on runoff (KOENIGER et al., 2008). The solid phases of precipitation, i.e. snow, almost do not undergo isotopic exchange with atmospheric water vapour as they fall; instead, they conserve the isotopic composition formed in the cloud (GAT, 1996). On the ground, the initial isotope signal of the snow layers may be modified by drifting, water vapour diffusion in the snowpack, condensation of water vapour on the snowpack, deposition of rainwater, sublimation into the atmosphere, or partial melting and percolation of the melted water. Most commonly, metamorphism and the subsequent melting of the snowpack reduces the initial isotopic variability in the snow cover (COOPER, 1998; STICHLER & SCHOTTERER, 2000). In the context of runoff separation modelling at relatively small scales JUDY et al. (1970) recommended an evaluation of spatial variations in isotope content of a snow cover with large elevation differences before isotope variations can be applied to studies of snowmelt runoff. In addition, KOENIGER et al. (2008) showed that snow isotopic composition can provide a useful parameter to improve snowmelt hydrograph separations under varying scenarios.
Recent climate warming and changes in atmospheric circulation patterns have resulted in reductions in the duration of the snow cover season, the amount of water stored in the snowpack, as well as a widespread trend toward earlier melt. Comparison of water balance for periods 196190 and 19712000 showed that in Slovenia average precipitation amount remained the same in both periods while runoff decreased and the evaporation increased recently (DOLINAR et al., 2008).
We selected for proposed investigations the area of Julian Alps (NW Slovenia) that represents the upper catchment area of river Sava. The area is characterised by high precipitation amount (1500 to > 3500 mm), rapid runoffs (> 2500 mm) and low evaporation (< 550 mm) (DOLINAR et al., 2008). Snow cover is regular, starts to accumulate in late autumn and lasts more than 100 days. Due to positive temperature trend snow cover period is changing and consequently the discharge regime is affected (FRANTAR et al., 2008).
However, spatial and temporal variability of snow and its isotopic composition, as well as snow cover contribution to the water balance in Julian Alps remains poorly investigated. Therefore, the aim of proposed investigations is to improve the knowledge on snowpack isotope characteristics and processes in it, and consequently to enable better understanding of water balance with emphasize on recharge of important Slovene aquifers.
