Contribution of glacier melt to runoff under climate change using a conceptual hydrological model in selected high alpine regions in Austria

The timing and quantity of snow and ice melt in high-alpine regions is of great importance, especially for time-sensitive processes such as hydropower production. In most conceptual hydrological models, the simulations of these components are frequently only based on simple temperature index methods, and the question arises whether these are sufficient to derive useful information on changing runoff seasonality and quantities for hydropower producers.

This study examines the quantitative and seasonal changes in glacier melt contribution to total runoff under climate change in several Austrian high-alpine catchments with hydropower production (Stubaital, Stubachtal, Kölnbrein/Maltatal, Schlegeis/Zillertal). As the estimation of precipitation model inputs for areas with complex terrain is characterised by a high degree of uncertainty, an undercatch-correction adapted for high-alpine areas was applied, integrating information from local weather stations, topography and iterative feedback from the modelled water balance. The conceptual, semi-distributed rainfall-runoff model COSERO was set up for the case study regions.  To cover long-term changes, the model was run for Stubai- and Stubachtal for the reference period (1990-2020) and future scenarios (2021-2100) with daily timesteps. In addition to the daily timesteps, COSERO was also coupled with the physically-based snowpack model Alpine3D for simulations in the Kölnbrein and Schlegeis catchments for recent decades to implement the simulation of relevant components of the water balance including snow and ice processes at an hourly timestep based on more complex energy-balance modelling. Besides air temperature and precipitation, the coupling requires additional hourly meteorological input such as radiation, relative humidity and wind information.

The combination of COSERO with Alpine3D improves results at the hourly timestep, but the conceptual model delivers satisfying results on its own as well. Moreover, the results are in line with literature and show the expected decrease of ice volume and ice melt in coming years. By 2050, the ice melt contribution to total runoff is significantly reduced in all case study areas and seasonality shifts due to less ice melt and earlier snowmelt in the form of more winter and spring runoff and less flow in summer are prevalent. In addition, we show that the modelling of the water balance components in the past can be greatly improved by using the undercatch-corrected precipitation data.

 

Acknowledgements: We thank the VERBUND Energy4Business GmbH, the Austrian Climate Research Programme (ACRP), the Austrian Research Promotion Agency (FFG), and the ÖBB for funding, fruitful discussions and providing us with data.