The Role of Hydropower in Climate-Resilient Energy Systems: Case Study of the Jeziorsko Reservoir (Poland).

Hydropower supports the energy transition by providing flexible, low-carbon generation, yet its performance is increasingly constrained by climate-driven variability in water availability. This study quantifies long-term hydroclimatic changes in the Warta River–Jeziorsko reservoir system (central Poland) and assess their implications for water resources, hydropower generation, and reservoir operation. The analysis combines multi-decadal meteorological observations, daily river flows at the Sieradz gauge (1951–2022), and reservoir and plant operational records, with electricity production evaluated for 1995–2022. The results indicate significant warming and shorter snow-cover duration, while annual precipitation shows no consistent long-term trend. Hydrological drought has intensified, reflected by lower mean flows in recent decades and a strong increase in days with discharge below SNQ, particularly after 2015. Electricity production is highly variable and shows a significant downward trend, amplified by reduced usable storage following operating-rule changes. By linking long-term hydroclimatic indicators with site-specific operational and production data for a lowland multi-purpose reservoir under environmental constraints, this study provides evidence to support adaptive reservoir management balancing water security and hydropower reliability.