a) Storuman, S0 without environmental flow 600
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electricity production when introducing a range of environmental flow options that have the potential to promote ecosystem functions or habitat conditions for riverine organisms. The simulation software One-area Power-Market Simulator (SINTEF, 2023) was also used. The researchers based the 13 environmental flow options on combinations of four components: 1. Prohibiting zero-flow events by requiring a minimum water flow through the station at all times, to prevent stretches of the river system becoming completely dry
2. Matching seasonal water flow, with flow levels higher in spring and lower in summer, to promote the growth of vegetation alongside waterways
3. Ensuring the release of water into fishways – areas of the river system intended to enable the movement of various fish species
4. Ensuring the release of water into bypass channels – areas of the system that directly connect stretches of river upstream and downstream of a hydropower facility.
As the authors explained, introducing environmental flow measures like the ones analysed in their present study offer the opportunity to mitigate negative effects on riverine ecosystems caused by the combined stress of hydropower production and climate change, helping to avoid the most harmful flow and water-level events while increasing ecosystem resilience. They go on to give the example of the Storuman hydropower station. Here the duration of zero-flow events was projected to increase during hydrologically dry years in the future, with a 18% increase in the climate of 2040 compared to 1981–2010. However such a risk can be alleviated by introducing rules for continuous discharge. Overall, the climate models predicted higher water runoff entering the river system in future scenarios than under recent conditions, with average annual water discharge at the hydropower station at the mouth of the Ume River predicted to be 1.8% greater in 2030 and 2.2% greater in 2040. The models also predicted seasonal changes, with lower runoff levels from June to October and higher levels from October to May. Without any environmental flow management and taking into account hydropower operations, regulated flow in the river was not projected to change significantly under future scenarios. However, under these conditions there would be a reduction in seasonal variation in water flow. The difference between annual maximum and minimum flows at the river-mouth station under 2040 conditions was predicted to be 17% lower under the 2040 climate scenario than recent conditions. Overall hydropower production without
environmental flow restrictions would rise by 2.6% under a 2040 climate compared to recent conditions. Under six of the environmental flow options, projected power production under 2040 conditions looked higher than recent conditions without any environmental flow restrictions. Power production variability through the year was projected to reduce under 2040 conditions, primarily due to a less extreme dip in April. This study demonstrates the feasibility of introducing
environmental flow actions in Sweden, and other regions where increases in runoff are projected, with sustained hydropower production, having large benefits for riverine biodiversity and enhancing resilience of riverine ecosystems to climate change. Indeed, the environmental benefits of such management in this area would be especially significant in the future, when
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b) Storuman, S9 with environmental flow 600
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Above: a) Hydrographs for the Storuman hydropower station with current hydropower operation rules for mean conditions with current and future (2030) climates, along with hydrographs for hydrologically extreme years: A high spring flood year (based on 1995), a dry year (based on 1996), and a wet year (based on 1998). (b) Hydrographs for the Storuman Storuman discharge with environmental flows according to scenario 9, for mean conditions with present and future (2030) climates, along with hydrographs for hydrologically extreme years: A high spring flood year (1995), a dry year (1996), and a wet year (1998). Source Widen et al in
https://doi.org/10.1016/j.scitotenv.2024.176622
biodiversity is likely to be under increasing pressure from climate change impacts. However, the researchers encourage an understanding of the interactions between environmental protection and power production on a case-by-case basis when determining optimal flow management options. Projected flow increases in a catchment can facilitate environmental flows, but also raises important questions about whether to allocate flow to ecosystem rehabilitation versus increasing renewable electricity production, since both can be argued to contribute to climate change mitigation, they add. In addition, any increase in hydrological extremes may lead to situations where meeting environmental flow demands might conflict with hydropower production if negative effects in riverine ecosystems and organisms are to be avoided. This is why the authors suggest further studies
are needed to understand the consequences of environmental flow management in regions where water scarcity is expected to increase in a future climate, since the challenges of meeting the requirements of all users may be greater. Collaboration among stakeholders will also be required for successful outcomes.
References
https://afry.com/en/events/potential-increased-capacity-and-balancing-swedish- hydro-power
Environmental flows in a future climate: Balancing hydropower production and ecosystem rehabilitation in the Ume River system, Sweden. Åsa Widen, Birgitta Malm Renofalt, Roland Jansson. Science of the Total Environment 955 (2024) 176622.
https://doi.org/10.1016/j. scitotenv.2024.176622
https://environment.ec.europa.eu/news/water-flow-management-can-support- hydropower-production-while-protecting-river-ecosystems-swedish-2025-07-03_en
www.waterpowermagazine.com | October 2025 | 21
Below: Akkats power plant near Jokkmokk, Sweden. The paintings adorn the gates of the power plant, which is also a popular tourist attraction, symbolising the Sami way of life and culture, which is a major feature of this part of northern Sweden © Lasse Johansson /
Shutterstock.com
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S0-High spring flood (Current) S0-Dry (Current) S0-Wet (Current) S0 Average (Current) S0-High spring flood (2040) S0-Dry (2040 S0-1998 (2040) S0 Average (2040)
S9-High spring flood (Current) S9-Dry (Current) S9-Wet (Current) S9 Average (Current) S9-High spring flood (2040) S9-Dry (2040 S9-Wet (2040) S9 Average (2040)
Flow (m3
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Flow (m3
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