The contribution of snow meltwater to catchment streamflow can be quantified through hydrograph separation analyses for which stable water isotopes (18O, 2H) are used as environmental tracers. For this, the spatial and temporal variability of the isotopic composition of meltwater needs to be captured by the sampling method. This study compares an optimized snowmelt lysimeter system and an unheated precipitation collector with focus on their ability to capture snowmelt rates and the isotopic composition of snowmelt. The snowmelt lysimeter system consists of three individual unenclosed lysimeters at ground level with a surface of 0.14 m2 each. The unheated precipitation collector consists of a 30 cm-long, extended funnel with its orifice at 2.3 m above ground. Daily snowmelt samples were collected with both systems during two snowfall-snowmelt periods in 2016. The snowmelt lysimeter system provided more accurate measurements of natural melt rates and allowed for capturing the small-scale variability of snowmelt process at the plot scale, such as lateral meltwater flow from the surrounding snowpack. Because of the restricted volume of the extended funnel, daily melt rates from the unheated precipitation collector were up to 43% smaller compared to the snowmelt lysimeter system. Overall, both snowmelt collection methods captured the general temporal evolution of the isotopic signature in snowmelt.
In this study a 25-year (1976-2000) series of observed precipitation, temperature, runoff and further water-flows of a lysimeter balance within the pre-alpine research catchment Rietholzbach (Switzerland) is analyzed. The comparison of the precipitation volumes on this lysimeter to precipitation collected by a conventional rain gauge shows that conventional rain gauges provide strongly underestimated values for precipitation, especially in winter. The obtained monthly precipitation correction factors indicate that precipitation losses above 20% for rain and above 50% for snow are realistic. The observed hydrometeorological values allowed for improving the understanding of the model-based simulation of the hydrological processes with distributed hydrological models and for investigating both a conceptual and a physically based runoff-generation approach. The albedo, soil moisture and lysimeter water balance allowed for a simultaneous assessment of the performance of several model components, such as the soil moisture, runoff-generation and evapotranspiration modules and the module for the determination of snow cover accumulation and melt. and V príspevku sú analyzované 25-ročné rady zrážok, teploty vzduchu, odtoku a hydrologickej bilancie v lyzimetri vo výskumnom povodí Rietholzbach (Švajčiarsko). Porovnanie zrážok zachytených lyzimetrom a konvenčným zrážkomerom ukazuje, že údaje zo zrážkomera sú veľmi podhodnotené, najmä v zime. Podľa získaných mesačných koeficientov opráv zrážok sú straty zrážok vyše 20 % pre dážď a vyše 50 % pre sneh realistické. Pozorované meteorologické údaje umožnili lepšie pochopiť simuláciu hydrologických procesov pomocou distribuovaných hydrologických modelov a pomohli pri posudzovaní konceptuálneho aj fyzikálne založeného prístupu k modelovaniu tvorby odtoku. Albedo, vlhkosť pôdy a hydrologická bilancia lyzimetra umožnili posúdiť funkciu niekoľkých zložiek modelu (moduly vlhkosti pôdy, tvorby odtoku, evapotranpirácie a akumulácie a topenia snehu).