Regional impacts of offshore wind farms on the North Sea hydrodynamics

Offshore wind energy is essential for expanding renewable energy generation and reducing global greenhouse gas emissions. However, as offshore wind turbines form new elements in the marine environment, the offshore wind infrastructure has implications for the physics of the atmosphere and ocean. In this study, we demonstrate the effects of surface wind speed reduction and structure-induced mixing, and illustrate the consequences for ocean dynamics in the southern North Sea. Using unstructured grid modeling, we present simplified parameterizations to account for wind speed reduction due to offshore wind farms and the underwater structure drag by offshore wind turbine foundations in hydrodynamic models. The simulations cover the seasonal cycle of the summer stratification, while taking into account the recent state of European offshore wind development in the southern North Sea. The modeling shows that offshore wind farm effects cause large-scale structural changes in ocean physics, systematically affecting the North Sea hydrodynamics. The wake effects at offshore wind farms lead to spatial redistributions of horizontal currents and, in particular, affect the seasonal stratification development on regional scales. Although these perturbations are on the order of natural variability, changes in regional stratification suggest potential consequences for biogeochemical processes and marine ecosystem dynamics. With our results, we provide new insights into the adaptation of coastal seas to offshore wind farm effects and raise awareness for potential changes in the future coastal ocean and the southern North Sea.