Hydropower (potential and kinetic energy) is one of the most important renewable energy sources in the world. This energy is directly dependent on water resources and the hydrological cycle. Ongoing climate changes are likely to influence the availability/amount of this energy resource. The present study explores the relationship between climate changes and river runoff, projects future runoff in both gauged and ungauged river catchments, and then assesses how these alterations may affect the future hydropower resources in Lithuania. Runoff projections of the gauged rivers were evaluated applying Swedish Department of Climate hydrological model, and runoff of ungauged river catchments were estimated by created isoline maps of specific runoff. According to an ensemble of three climate models and two Representative Concentration Pathway scenarios, runoff and hydroelectric energy projections were evaluated for two future periods (2021–2040, 2081–2100). The results demonstrated a decrease in future river runoff. Especially significant changes are expected according to the most pessimistic RCP8.5 scenario at the end of the century. The projected changes are likely to bring a negative effect on hydropower production in the country. These findings could help understand what kind of benefits and challenges water resource managers may face in the future.

Tvenkiniai daro įtaką reguliuotų upių vandens organizmams, upės nuotėkiui, tvenkinio krantams ir upės vagai, požeminiams vandenims bei kraštovaizdžiui. Šiuo metu galiojantys teisės aktai reglamentuoja gamtosaugos debitą kaip 30 parų minimalaus debito dalį. Šis debitas tenkina tik minimalius vandens ekosistemos poreikius ir nepriklauso nuo metų vandeningumo. Tokia gamtosaugos debito apskaičiavimo praktika hidroelektrinėms palieka hidropikingo galimybę. Straipsnyje aptariami kai kurie Lietuvos mažų ir vidutinių upių tvenkinių eksploatacijos aspektai. Siūloma vietoje gamtosaugos debito reguliuotai upei žemiau tvenkinio nustatyti ekologinį nuotėkį. Svarbiausia sąlyga apskaičiuojant ekologinį nuotėkį – tvenkinio lygių ir reguliuotos upės debitų kaitos panašumas su natūralių ežerų ir upių režimu. Nustatyta, kad neištirtų upių prietaka į tvenkinį ir ekologinis nuotėkis gali būti apskaičiuoti iš atraminių vandens matavimo stočių duomenų kiekviename 15 Lietuvos upių baseinų. Siekiant reguliuotų upių geros ekologinės būklės, siūloma tobulinti HE turbinas, leidžiančias naudoti upės nuotėkį HE plačiame debitų kaitos intervale, išvengiant pikinio darbo režimo (hidropikingo).

Hydropower remains the most important and largest source of renewable energy. However, besides many additional benefits, such as dams for water supply, irrigation, flood control, recreation, navigation, etc., hydropower generation has a negative impact on the environment. This study aimed to investigate the hydrologic changes in Lithuanian lowland rivers caused by small hydropower plants (HPPs). Thirty-two indicators of hydrologic alteration (IHA) were studied in 11 rivers downstream of hydropower plants in the post-impact and pre-impact periods. The findings showed that HPPs and reservoirs considerably disturbed the primary flow of river ecosystems downstream. The largest changes in mean IHA values were found for low and high pulse characteristics (up to 57%) and the number of reversals (up to 44%). Only small or no deviations of the timing of annual extreme flows were found. The number of reversals, a low pulse count, and a fall rate were the flow characteristics that fell outside their historical ranges of variability most often. Six (out of 11) hydropower plants were identified that provoked hydrologic alterations of a moderate degree.