| Summary: | Abstract Snow plays a significant role in hydrological studies in cold climates because of its importance for runoff and recharge, provision of water for water supply and energy production, etc. In this thesis, we evaluated snow, with a particular focus on snowmelt processes, from the perspective of stable water isotope (δ18O and δ2H) hydrology. δ18O and δ2H isotopes possess unique fingerprinting properties and are valuable in various snow hydrological applications, including source water identification, quantitative partitioning of water sources and their mixing, and estimating water residence times within catchments. We aimed to answer the following research questions: (i) how do isotope values change vertically across the snow layers in the snowpack? (ii) how do snowmelt isotope values evolve spatiotemporally? and (iii) how do different sampling methods and mathematical approximations of meltwater isotopes influence the extent of potential bias in estimating snowmelt water’s contribution to streamflow? An analysis of the isotope datasets revealed distinct isotopic stratigraphy in the snowpack layers over winter, with an enriched base layer and spatially consistent stratigraphy across the Pallas catchment. Vertical isotope profiles homogenized during the peak melt period, showing an average of 1 to 2‰ higher δ18O values than before melting. Snowmelt rate influenced liquid-ice fractionation, with pronounced fractionation effects during low melt rates, leading to the depletion of heavy isotopes in initial meltwater samples. Before the peak melt period, meltwater was isotopically heavier and more variable than the depth-integrated snowpack, exhibiting a disparity of approximately 3.1‰ in δ18O, which diminished during the peak melt period. By using δ18O data from snowfall, snowpack, and meltwater, we quantified the biases and estimated the total contribution of snowmelt water to streamflow during the snowmelt period. If meltwater samples are unavailable, snowpack isotopes during peak melt period can yield ...
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