Water flow management can support hydropower production while protecting river ecosystems, Swedish study finds

Hydropower forms a critical part of renewable energy production systems in many countries. However, hydropower installations interfere with natural water flow and degrade river ecosystems, which are already among the most sensitive environments to climate change, being altered by temperature and hydrological change.

Many hydropower operations in the EU are implementing ‘environmental flow’ assessment schemes to combat this, often to comply with environmental targets set by the Water Framework Directive. Environmental flow assessments define the water flows needed to sustain a river ecosystem and its services, considering the quantity, quality and temporal pattern of flow. As climate change will bring consequences for hydropower in coming years, these assessments – and related policy – must consider climatic change impacts that may occur over longer time frames. While crucial for environmental sustainability, such initiatives can limit power output and performance, and must therefore be balanced with the need to ensure sufficient, continued supply of renewable energy in various climate scenarios.

The study assessed the effect of 13 different environmental flow management options on ecosystem functioning, on habitat condition, and on power production in the Ume River catchment of Northern Sweden. The area contains 19 hydropower stations. Researchers assessed the performance of each station under each flow option for both recent (1981-2010) and predicted future climate conditions using the IPCC scenario A1B of moderate global greenhouse gas emissions and high economic growth to model future conditions. They ran each model over an 83-year period (based on historical records for 1931-2013), and used the annual mean averages to inform projections of how hydropower would most likely be affected in the years 2025, 2030 and 2040.

The researchers based the 13 environmental flow options on combinations of four components:

• 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
• Matching seasonal water flow, with flow levels higher in spring and lower in summer, to promote the growth of vegetation alongside waterways
• Ensuring the release of water into fishways – areas of the river system intended to enable the movement of various fish species
• 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.

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[1]. The models also predicted seasonal changes, with lower runoff levels from June to October and higher levels from October to May - likely due to reduced snow formation, allowing more precipitation to run off during winter and providing less snowmelt in spring and summer.

They found that without any environmental flow management, the regulated flow in the river, taking into account the hydropower operations, 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.

The results indicated that it would be feasible to implement environmental flow management in this catchment under future climate conditions in Sweden. They noted that the environmental benefits of such management in this area would be especially significant in the future, when biodiversity is likely to be under increasing pressure from climate change impacts. They suggested that increased water runoff due to climate change could benefit both hydropower and biodiversity, with flow management – although management schemes may limit the potential for hydropeaking (increasing flow to raise power output during periods of high electricity demand). 

The study used weekly water flow data, and therefore did not consider water flow or power production issues occurring over shorter periods. The models did not account for the potential increased frequency and severity of extreme weather events under future climates.

The researchers highlighted the importance of understanding the interactions between environmental protection and power production in individual cases to determine optimal flow management options. They suggested that further studies were 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.

Source

Widén, Å., Renöfält, B. M. and Jansson, R. (2024) Environmental flows in a future climate: Balancing hydropower production and ecosystem rehabilitation in the Ume River system, Sweden. Science of The Total Environment 955:176622. https://doi.org/10.1016/j.scitotenv.2024.176622

[1] Northern Sweden is expected to experience higher rainfall under climate change, particularly in autumn and winter, leading to higher runoff volumes. Earlier snowmelt will be another contributing factor. (E.g. Salmonsson, T., 2013. Assessing the impacts of climate change on runoff along a climatic gradient of Sweden using PERSiST.)