Large‑scale construction of offshore wind farms in the North Sea could lead to reduced precipitation in coastal areas of Denmark, Germany, the Netherlands, and the United Kingdom. This is the conclusion of researchers from the Helmholtz Centre Hereon and the University of Hamburg in Germany. According to their calculations, under the maximum development of sea zones already designated for wind energy, precipitation in some coastal areas could decrease by 8‑15%, and in some parts of the Danish Jutland peninsula by more than 15%. At the same time, directly over the wind farms themselves, rainfall would actually increase.
Today, Europe has about 34 GW of installed offshore wind capacity, but by 2030 the European Union aims to increase it to 60 GW, and by 2050 to 300 GW. A significant portion of the new capacity will be built in the North Sea. The countries of the region have agreed to jointly develop at least 260 GW of offshore wind energy there by mid‑century. The researchers therefore decided to investigate how such large‑scale construction could affect rainfall in coastal regions.
For this, they used the regional climate model COSMO‑CLM, which allows the impact of wind turbines on air movement to be taken into account. They considered three development scenarios for offshore wind energy: the actual layout of wind farms in 2023, the plans for 2030, and a maximum scenario after 2050, in which wind farms occupy all sea zones designated for their construction. The calculations covered ten years of weather conditions – from 2008 to 2017. For the 2030 scenario, 10 MW turbines were used, and for the maximum scenario, installations of 5, 10, and 15 MW were compared.
Wind turbines extract energy from moving air and thereby slow it down. Extensive areas of reduced wind speed and increased turbulence form behind large wind farms, and under certain atmospheric conditions, such a wake can extend for 50‑70 km. With a large number of turbines, these changes begin to affect air mass movement on a regional scale. In the maximum scenario, wind speed at a height of 10 m above the sea surface in the wind farm areas decreased by 2‑3 m/s.
At the same time, turbines enhance vertical mixing of the air. Moist marine air rises more actively, promoting cloud formation and precipitation directly over the wind farms. In the post‑2050 scenarios, precipitation in these areas increased by 8‑10 mm per month, or 12‑18%. As a result, the air masses that later move toward land contain less moisture, so precipitation further inland decreases.
This effect was most pronounced in Denmark. In some areas of Jutland, the reduction in precipitation exceeded 15%. Particularly noticeable changes were shown by the model in the area of Herning, located downwind about 80 km from the large planned zone Nordsøen I off the west coast of Denmark. In the north‑west of the German state of Schleswig‑Holstein and in coastal areas of Lower Saxony, precipitation decreased by about 5‑8%. A comparable reduction was observed over most of the Netherlands, while wind farms in the Irish Sea led to a decrease in precipitation of about 5‑8% in western Britain.
Wind direction plays a key role. South‑westerly winds prevail over the North Sea, carrying moist air toward the European coast. It was under this direction that the influence of wind farms was strongest: over them, precipitation increased by 9‑20%, while in adjacent coastal areas it decreased by about 5‑8%. Under north‑westerly winds, the model showed virtually no noticeable effect on land precipitation. The effect was most pronounced in autumn and winter, when the reduction in precipitation locally reached 10‑20%. In spring, the effect was weaker, and for summer no consistent changes were found.
The researchers also found that wind farms change not so much the number of rainy days as the intensity of rainfall. For example, in central Jutland, the number of days with precipitation remained practically unchanged, but heavy rains became less intense. Over the wind farms located in front of the coast, the opposite occurred: the number of precipitation events increased by about 3%, while their intensity also increased.
Under the current scale of offshore wind energy and in the development scenario up to 2030, the model showed virtually no noticeable effect on land precipitation. Significant changes arose only under the maximum density scenario for sea area development after 2050. The scientists emphasize that this scenario represents an upper bound for possible industry development, and the calculations themselves were performed with a single climate model. The next step should therefore be studies using other models, various densities, and different wind farm layouts.
