River hydro-energy potential assessment: balancing renewable energy opportunities with environmental-climatic constraints

The main objective of the study was to analyze the technical hydroenergy potential (HTP) of rivers in the upper Vistula basin (Poland, Central Europe), taking into account environmental constraints (the need to maintain environmental flows) and climatic constraints (occurrence of meteorological droughts). The study covered nine catchments with diverse physiographic conditions: mountainous, upland, and lowland. The research was carried out in the following stages: analysis of the formation of exploitable water resources, determination of the hydroenergy potential of the catchments, analysis of meteorological droughts using the Standardized Precipitation Evapotranspiration Index (SPEI), and identification of relationships between SPEI values and HTP potential. The results showed that the highest hydroenergy potential is characteristic of mountainous catchments, and the lowest of lowland ones. Maintaining environmental flows, determined using the new Global Index method, reduces by an average of 20% the water resources available for energy production. The analysis of the SPEI drought index revealed distinct, synchronous episodes of drought and wetness, driven by regional climatic patterns, with lowland catchments being the most susceptible to drought. A strong correlation was found between SPEI values and HTP potential, which increased with the length of the accumulation period of the index. This relationship was strongest in mountainous catchments and weakest in lowland ones. The study highlights the necessity of integrated and flexible water management planning that combines energy objectives with ecosystem protection and takes into account climatic variability, in order to ensure the sustainable development of hydropower.