Can tidal energy extraction counteract sea-level rise impacts?

The impacts of tidal energy development on the environment, ranging from species to habitats to oceanographic systems, remain uncertain, and gaps persist in current research. Most studies to date have focused on the impacts relating to collision, noise, displacement, and localised hydrodynamic changes that affect sedimentation transport and benthic species composition. There have been limited studies on the impacts of tidal energy on habitats, species distributions (especially mobile, pelagic species), and the wider ecosystem. There has also been no consideration of cumulative environmental impacts of energy extraction at multiple sites, and few studies have considered the comparative impacts of climate change.

Here, we simulate the tides in the Celtic Sea using the multi-scale unstructured mesh numerical model, Thetis.  Spatially varying sea-level rise is applied to these models for the first time, using data from the AR6 IPCC assessment, to examine the impact of sea-level rise on tidal dynamics. Shared Socioeconomic Pathways (SSPs) 1.19 through to 5.85 at the 50% confidence interval for years 2050, 2100, and 2150 are used to predict sea-level rise under different scenarios. 

Results show that tidal range (m) and maximum velocity (m/s) are likely to generally increase over time and with SSP scenario. Tidal range increases are particularly high in the Severn Estuary (up to 0.5 m increase) and, to a lesser extent, in the wider Celtic Sea (up to 0.1 m). Sea level-rise is expected to add between 0.28 and 2.01% to the maximum tidal range within the Celtic Sea. This is in addition to predicted sea-level rise.  Conversely, when adding tidal energy arrays into current tidal model conditions, tidal range tends to decrease across the south of the domain area, with a small increase in tidal range between Northern Ireland and North-west Scotland, followed by a mix of small increases and decreases off the Scottish coast. Overall, the installation of tidal arrays is expected to decrease the maximum tidal range by 10%. This keeps pace with increasing relative sea-level rise, demonstrating that possible sea-level rise and tidal array installation may complement each other to offset predicted changes to tidal dynamics.

Under SSP scenarios, maximum velocity is predicted to increase between some islands off the coast of North-west Scotland, and between Morecambe Bay and the River Dee. These predicted changes may affect the efficiency of tidal energy development over time, as well as affect species distributions in localised environments where high levels of change are predicted.

Unsurprisingly, with the presence of tidal arrays, maximum speed is predicted to generally decrease across the Celtic Sea, with some small increases expected between islands off the North-west Scottish coast. When incorporating predicted sea-level rise, the level change is minimal, demonstrating that tidal arrays are more likely to have an impact on tidal velocity and that sea-level changes are unlikely to affect velocities enough to significantly reduce tidal energy efficiency.  Further work is being considered on optimising tidal array installations to suitably offset predicted relative sea-level rise and maintain energy production levels.