SREP-DROUGHT (Sep 2014 - Aug 2017) will evaluate how summer low flows and droughts are affected by winter snowpack in three catchments Alpbach (Prealps, central Switzerland), Kamenice (Jizera Mountains, northern Czech Republic), and Gudjaretis-Tskali (Little Caucasus, central Georgia). Two GIS-based rainfall-runoff models will simulate more than 10 years of runoff in streams by means of measured rain- and snowfall, other meteorological variables. We also use information on the geographical settings (features) of the catchments and knowledge of the main hydrological processes involved that transform rainfall into streamflow. These processes in the selected mountainous catchments include snow accumulation and melt, evapotranspiration, recharge and subsurface storage until the summer outflow, and will be studied by means of environmental isotopes 18O and 2H. This knowledge will result in parameters such as contribution of snowmelt water in the streamflow and time the water spends in the underground between snowmelt recharge and outflow. The obtained parameters will be employed for improvement of the models and therefore for a better simulation of runoff in snowmelt-dominated catchments. This approach will be tested at two catchment scales (small catchment 1-2 km2 and larger catchment 100-200 km2) in all three countries. The results will improve the performance of the GIS-based rainfall-runoff models, examine their potential of further development through comparison in different catchments, and allow better prediction of low flow periods in various mountain zones across Europe.