Water availability assessment for run-of-river hydropower under future climate change in the UK and Ireland

In the United Kingdom (UK), the amount of electricity generated from small-scale hydropower has nearly tripled since 2010. One of the key areas of growth within the sector has been run-of-river 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 hydropower generation and the total power output potential.

In this study, we quantify the impact of a worst-case future climate change scenario (Representative Concentration Pathway 8.5) on the generation potential of run-of-river hydropower schemes in the UK and RoI. EXP-HYDRO hydrological model is used to simulate future daily streamflow for the 2021-2080 hydrological years in 178 catchments containing 531 hydropower abstractions. We estimate daily abstraction potential at each site based on the local environmental regulators’ (for Scotland, England, Wales, Northern Ireland, and Ireland) general abstraction conditions. We then perform seasonal and annual Mann-Kendall trend analysis at each site to analyse changes in: 1) the number of days when abstraction is possible, 2) the number of days when maximum abstraction is reached, 3) mean abstraction volume on days when abstraction is possible, and 4) the total abstractable volume. The scale of study undertaken allows for characterisation of both the impact of regional variation in future climate forcing, as well as analysis of the impact of local environmental regulation, on the future generation potential of run-of-river hydropower in the UK and RoI.

Results show increasing annual total abstraction potential in northern England and Scotland, while a decline is seen in Wales; little change is seen in Ireland and Northern Ireland. The number of days per year that abstraction is possible declines in all areas except the northwest of Scotland, while the number of days that maximum allowable abstraction is reached increases; mean daily abstraction therefore increases. A disparity can be seen in different nations between the magnitude, and in some cases direction, of change in annual mean streamflows compared to annual abstraction potential. This is likely caused by differences in water abstraction regulations between UK nations. This poses an interesting question in terms of the impact of environmental regulations for the different nations of the UK, and how best to maximise renewable energy output by hydropower, while protecting the natural environment.