Modelling the Impact of Offshore Wind Farms on the Coastal Atmosphere and Ocean off Western Iberia

We investigate the impact of offshore wind farms (OWFs) on the coastal atmosphere and ocean off western Iberia by comparing two five-year (2009–2013) dynamical downscaling simulations performed with the Weather Research and Forecasting (WRF) regional model. One simulation includes a wind farm parameterization (WFP) scheme, while the other does not, enabling a direct assessment of turbine-induced modifications to local wind patterns and ocean circulation associated with upwelling. Winds in this region are typically stronger in summer and predominantly from the north, and upwelling dominates along most of the region in the baseline scenario. Maximum reductions of approximately 12.5% in wind speed at 10 meters, averaged over the five-year period, were identified in the wind farm areas with the highest number of turbines, with wakes extending more than 125 km downwind and oriented southward. Summer exhibited the strongest wind reductions and longest wake extensions. Wind deficits were also evident aloft, with maxima between 100 and 150 m, encompassing the hub height, where the flow directly impacts the rotor. Near-surface wind wakes generate horizontal gradients in wind stress within the wind farm areas, producing zones of surface-water divergence and convergence and driving vertical ocean motions. Turbine-induced upwelling is expected to occur on the offshore side of the farms and downwelling on the onshore side, forming dipoles that can extend over 100 km and are predominantly oriented southward. Five zonal transects crossing the OWFs at different latitudes – approximately perpendicular to the dominant wind-wake direction – provide indications of these dipoles and interactions between dipoles from neighboring farms, forming double dipoles in some cases. Integration along these transects indicates that weakening of upwelling, resulting from the combined effects of Ekman pumping and coastal upwelling, is the most recurrent outcome throughout the year, particularly during summer. This reduction in upwelling is also expected to have an impact in nutrient concentrations and primary productivity in the studied regions. These projected results provide insights into the potential response of the coastal atmosphere–ocean system to wind energy extraction, highlighting the need to consider coupled interactions in OWF planning.

Keywords: Offshore Wind Farms; Western Iberian Margin; Wind Farm Wakes; Upwelling; Weather Research and Forecasting (WRF); Wind Farm Parameterization