Current and future variability of water supply to a mountain reservoir (Polish Carpathians).

This study presents the characteristics of the current course of the phenomenon of droughts and floods in the catchment area of a man-made mountainous reservoir and forecasts of water inflow changes to the reservoir over the next three decades. The catchment area of the Klimkówka reservoir on the Ropa River, a tributary of the Wisłoka River, located within the Polish Carpathians was selected for the study. The analysis carried out, using Soil and Water Assessment Tool (SWAT) modelling among other techniques, showed an increase in the importance of low-flow outflow from the upper Ropa catchment and a negative balance of inflow to the reservoir (Q < 2 m3s−1), manifested by a prolonged duration of low flows and an increase in outflow deficit during the year. The duration of flood flows and the runoff excess during these periods show a constant or decreasing tendency, while the length and excess of runoff increase during large floods. Thus, in the upper Ropa catchment, an increase in the intensity of extreme hydrological phenomena is observed. The prepared forecasts indicate an increase in annual runoff from the catchment in the decades 2021–2030 and 2031–2040 and a marked decrease in the decade 2041–2050. In the annual cycle, the projected changes in the coming decades will take different directions. In December only, throughout the entire period 2021–2050, the outflow will increase, whereas in May it will systematically decrease. [ABSTRACT FROM AUTHOR]