In the United Kingdom (UK), the amount of electricity generated from small-scale hydropower (HP) has nearly tripled since 2010. One of the key areas of growth within the sector has been run-of-river (RoR) hydropower schemes, with several hundred now operating across the UK and the Republic of Ireland (RoI), the majority situated in mountainous areas of Scotland and Wales. Although the overall grid contribution of these schemes is small (~2%), they still play an important role, not only in decarbonising the grid and contributing to national emission reduction goals, but also at local scales, where schemes often provide financial benefit to local communities and individuals. However, future climate change threatens to alter precipitation patterns and therefore streamflows, potentially impacting both the timing of HP generation and the total power output potential.

Across the UK and RoI, environmental regulators in each of the five nations (England, Wales, Scotland, Northern Ireland, and Ireland) approach abstraction licencing for RoR HP in different ways. Varying protection is afforded to low-flows, high-flows, and flow variability, through different hands-off-flow volumes, maximum abstraction rates, and percentage take volumes, respectively. In this study, we examine the impact of these varying abstraction licence conditions on the ability of 531 RoR HP abstractions to make optimal use of future climate change influenced streamflows. We use the EXP-HYDRO hydrological model to simulate future daily streamflow for the 2021-2080 hydrological years under a worst-case future climate change scenario (Representative Concentration Pathway 8.5). Abstraction licence conditions for each of the five nations are then applied to all of the schemes individually, with results across the 60-year study period analysed. A comparison of key abstraction characteristics is then made, including, the number of days when abstraction is possible; the number of days when maximum abstraction is reached; mean abstraction volume on days when abstraction is possible; and total abstractable volume.

The work poses an interesting question in terms of the impact of environmental regulations for the RoI and the different nations of the UK, and how best to maximise renewable energy output by HP, while protecting the natural environment.