Observational evidence of offshore wind farm impacts on sea surface temperature in the North Sea

To meet the greenhouse gas targets of 2050, European countries plan a large expansion of offshore wind energy in the North Sea. This expansion is expected to cover 11% of the basin's surface area. The environmental impacts of this expansion are not fully understood yet. However, it is known that wind turbines alter the local microclimate by creating wakes, regions of decreased wind speed and enhanced turbulence. Mesoscale models are a promising tool to investigate the feedback effects of wind turbines on the environment. As such, recent studies show that offshore wind farms affect environmental factors such as sea surface temperature (SST). However, these studies are not conclusive and show both warming and cooling of SST induced by wind farms.

This study seeks to clarify the environmental feedback effects on SST of already installed wind farms using observations, as observational evidence of these effects remains limited. The study is focused on North Sea wind farms with over 100 turbines and examines both buoy measurements and satellite images. Time series of at least four years from before and after the construction of wind farms are investigated using conventional statistical models. Since buoy measurements are limited to a few offshore wind farms, satellite images provide additional spatial information and coverage at farms where buoy information is absent. In a second part of the study, the observational relationships between offshore wind farms and sea surface temperature derived from buoy and satellite data are used to train machine learning models. These models are then applied to projected offshore wind farm configurations to estimate potential future impacts on SST.

Preliminary results from observations show a consistent warming of SST in the wakes of large offshore wind farms, generally on the order of 0.2–0.5°C. This is in line with previous numerical modelling studies. The feedback effect of wind farms on SST has a strong seasonal component, being more pronounced in winter. During spring and summer months, SST cooling is also observed. Furthermore, a strong correlation with atmospheric stability is found, along with interdependent site variations. In future studies, these insights are expected to inform parameterizations in (coupled wave–ocean-)atmosphere mesoscale models.