California Current Upwelling

The California Current flows southward along the West Coast. Regular wind on the ocean surface pushes surface waters offshore. The combined actions of “coastal divergence” and “wind stress curl”  drive the phenomenon of  “upwelling”, which bring nutrient-rich water up to the surface that feed sizable populations of plankton. [1] In turn, the plankton are food for a diverse group of species including seabirds, fish, and marine mammals.  In California, the upwelling season is most noticeable in spring and summer.  

More research is needed but one high-resolution atmospheric model [WRF-WFP model] in conjunction with an ocean-circulation model of the United States West Coast [the ROMS ocean circulation model] suggested little effect in the 10-kilometer coastal band where upwelling is the strongest and an approximate reduction by 5% of wind speeds at 10 meters above surface level in the vicinity of the proposed wind farm. The modeling suggests little change on “coastal upwelling” and some impact on “wind stress curl-driven upwelling.”[1] The modeling was based on a scenario of 877 10 MW turbines located across Humboldt Bay Wind Energy Area (152 turbines), Morro Bay 399 Wind Energy Area (230 turbines), and Diablo Canyon (495 turbines) call areas. Only two of these areas have been leased. [3]

 “Subsurface temperatures along a transect at 35 °N show modest warming inshore of 50 km once simulated turbines were introduced in the environment, indicating reduced upwelling in this zone. This warming was accompanied by the cooling of subsurface waters offshore of 50km including enhanced upwelling and increased nutrient concentrations in these offshore waters.” [2] Overall, the net changes to upwelling when spread across a 100 kilometer coastal zone were “modest”. [1]  No significant impacts were observed for other atmospheric fields associated with wind turbines (e.g. e.g. precipitation, radiation, surface pressure).  Changes in upwelling “were more pronounced at Morro Bay and Diablo Canyon than they would be at Humboldt, likely due to relatively smaller footprint over which turbines were simulated at Humboldt.” [2]  

The model was designed to take into account a changing climate between 2020-2085 but did not take into account stratification changes in the water column from surface heat differences. Researchers have only run limited models but there may be regionwide reduced changes in “upwelling from offshore wind-energy development…in the face of intensifying winds due to climate change.” [2] More research is needed in this area because of the complexity of modeling winds and climate-change-induced changes at a regional scale. 

These models do not model the ecosystem but only model wind and ocean circulation. “The consequences of these changes in physical upwelling structure on the ecosystem are currently unknown and could potentially form future areas of investigation that could also include an assessment of fisheries and socio-economic effects.” [1] More information is needed to understand the impact of any changes to upwelling on phytoplankton, zooplankton, and krill. More data will need to be collected about “mixing and turbulence from wind-turbine-structures in the water column” that could impact wave patterns.  [2] 

The takeaway from these studies is that the interaction between offshore wind infrastructure and upwelling events is something that permit agencies need to be aware as they make decisions about where to site offshore wind infrastructure.

[1] Raghukumar, K., Nelson, T., Jacox, M. et al. (2023) Projected cross-shore changes in upwelling induced by offshore wind farm development along the California coast. Commun Earth Environ 4, 116. https://doi.org/10.1038/s43247-023-00780-y [Note: This study did not calculate “ecosystem responses” from physical oceanographic changes which includes modeling in additional factors including “alongshore wind stress, nutrient fluxes, and primary productivity”]; See also Raghukumar et al. (2022) Effect of Floating Offshore Wind Turbines on Atmospheric

Circulation in California, Frontiers in Energy Research, 10. https://www.frontiersin.org/articles/10.3389/fenrg.2022.863995/full

[2]  Raghukumar, K.; Nelson, T; Chang, G.; Chartrand, C.; Cheung, L. et al. (2020)  A Numerical Modeling Framework to Evaluate Effects of Offshore Wind Farms on California’s Coastal Upwelling Ecosystem. Publication Number: CEC-500-2024-006. https://www.energy.ca.gov/sites/default/files/2024-02/CEC-500-2024-006.pdf 

[3] Higher-capacity turbines (15 MW) could result in a lower density build out. Placement of turbines within a call area can also alter potential wind wakes that influence upwelling.