Importance of snowmelt contribution to seasonal runoff and summer low flows in Czechia

Abstract

<jats:p>Abstract. The streamflow seasonality in mountain catchments is often influenced by snow. However, a shift from snowfall to rain is expected in the future. Consequently, a decrease in snow storage and earlier snowmelt is predicted, which will cause changes not only in seasonal runoff distribution in snow-dominated catchments, but it may also affect the total annual runoff. The objectives of this study were to quantify (1) how inter-annual variations in snow storages affect spring and summer runoff, including summer low flows, and (2) the importance of snowmelt in generating runoff compared to rainfall. The snow storage, groundwater recharge and streamflow were simulated for 59 mountain catchments in Czechia in the period from 1980 to 2014 using a bucket-type catchment model. The model output was evaluated against observed daily runoff and snow water equivalent. Hypothetical scenarios were performed, which allowed for analysing the effect of inter-annual variations in snow storage on seasonal runoff separately from other components of the water balance. The results showed that 17 %–42 % (26 % on average) of the total runoff in the study catchments originates as snowmelt, despite the fact that only 12 %–37 % (20 % on average) of the precipitation falls as snow. This means that snow is more effective in generating catchment runoff compared to liquid precipitation. This was demonstrated by modelling experiments which showed that total annual runoff and groundwater recharge decrease in the case of a precipitation shift from snow to rain. In general, snow-poor years were clearly characterized by a lower snowmelt runoff contribution compared to snow-rich years in the analysed period. Additionally, snowmelt started earlier in these snow-poor years and caused lower groundwater recharge. This also affected summer baseflow. For most of the catchments, the lowest summer baseflow was reached in years with both relatively low summer precipitation and snow storage. This showed that summer low flows (directly related to baseflow) in our study catchments are not only a function of low precipitation and high evapotranspiration, but they are significantly affected by the previous winter snowpack. This effect might intensify drought periods in the future when generally less snow is expected. </jats:p>

Seasonal discharge response to temperature-driven changes in evaporation and snow processes in the Rhine Basin

“…As the dS2 model does not include dams and other reservoirs, this signal can be attributed to a change in discharge production. Secondly, a recent study investigating the response of several basins in Czechia to changes in snowmelt concluded that snowmelt started earlier in the year, which also reduced summer low flows via baseflow (Jenicek and Ledvinka, 2020). However, our study shows that low flows during September and October actually increased when only snow processes are considered.…”

“…The evaporation correction factor is included to correct any bias errors in the forcing data. According to Boussinesq's theory of sloping aquifers (Rupp and Selker, 2006) and the results found in Karlsen et al (2019), systems with higher slopes are expected to show higher discharge sensitivity values. Therefore, the discharge sensitivity parameters were defined as a linear function of the slope of each pixel, based on the hypothesis that regions with steeper slopes show a more responsive storage-discharge relation than regions with gentle slopes.…”

“…Firstly, higher temperatures affect the cryosphere: there will be less precipitation falling as snow, and there is more energy available to enhance melt from snow and ice. As snow stores are depleted earlier in the year, it affects the timing of the snowmelt peak in the discharge signal (Jenicek and Ledvinka, 2020;Beniston et al, 2018;Baraer et al, 2012;Huss, 2011;Hidalgo et al, 2009;Collins, 2008;Takala et al, 2009). Since meltwater from "water towers" is vital for billions of people (Viviroli et al, 2007), it is important to have a correct understanding of the expected changes in the cryosphere.…”

Assessing the degree of detail of temperature-based snow routines for runoff modelling in mountainous areas in central Europe

“…Nevertheless, the assumption that incoming solar radiation is well represented by air temperature does not al-ways hold, such as in high-elevation catchments where temperature seldom rises above the freezing point (Gabbi et al, 2014;Pellicciotti et al, 2005) or in conditions in which sublimation from the snowpack becomes a significant process (Herrero and Polo, 2016). Such issues led to the development of extended formulations including additional variables such as wind speed or relative humidity to improve the snowmelt estimation (Zuzel and Cox, 1975) or even hybrid methods combining energy-based and temperature-based approaches, such as the inclusion of a radiation component in temperature-based models (Hock, 1999;Kane et al, 1997).…”

Impacts of regional climate change on hydrological drought characteristics in headwaters of the Ore Mountains

“…Also, thanks to the combination of these factors, the summer droughts at CHA have not been as pronounced as in the KLI or ROT catchments so far. However, according to recent studies, the proneness of montane, mid-latitude catchments to summer water scarcity is expected to increase in the next decades in concordance with the ongoing warming (Bales et al, 2018;Brunner & Tallaksen, 2019;Hotovy & Jenicek, 2020;Jenicek & Ledvinka, 2020 Langhammer, & Beudert, 2015). This fact can be related with the usage of shorter data series, which did not cover the last decade.…”