The environmental implications of tidal stream energy extraction need to be evaluated against the potential climate change impacts on the marine environment. Here, we present how hypothetical very large tidal stream arrays and a "business as usual'' future climate scenario can change the hydrodynamics of a seasonally stratified shelf sea.
The Scottish Shelf Model, an unstructured grid three-dimensional ocean model, has been used to reproduce the present and the future state of the NW European continental shelf. Four scenarios have been modelled: present conditions and projected future climate in 2050 with and without very large scale tidal stream arrays in Scottish Waters (UK). This allows us to evaluate the potential effect of climate change on the hydrodynamics and compare it with the future state of the seas modified by large scale energy extraction.
It is found that where tidal range is reduced of by few cm by tidal stream energy extraction, it can help to counter extreme water levels associated with future sea level rise. Tidal velocities, and consequently tidal mixing, are also overall reduced by the action of the tidal turbine arrays. A key finding is that climate change and tidal energy extraction both act in the same direction, in terms of increasing stratification due to warming and reduced mixing, however, the effect of climate change is an order of magnitude larger.
The results presented in this work are the basis for other studies that evaluate the impacts of the above mentioned physical changes on animal behaviours, in particular the distributions of mobile predator and prey species, on sediment dynamics with special attention to water turbidity, and on benthic communities.