Seasonal Upwelling Forecasts in the California Current System.

Coastal upwelling plays a vital role in the support and maintenance of productive marine ecosystems throughout the California Current System (CCS). Here, we evaluate upwelling forecast skill using ∼30 years of seasonal reforecasts from four global climate models contributing to the North American Mulitmodel Ensemble (NMME). The models skillfully predict upwelling intensity throughout much of the CCS in boreal winter, and in the South‐Central CCS in spring/summer. The models also skillfully predict various aspects of upwelling phenology, including the timing of the spring transition, as well as the total vertical transport integrated over the course of the upwelling season. Climatic sources of forecast skill vary with season, with contributions from the El Niño‐Southern Oscillation in winter‐spring, and the North Pacific Oscillation and the North Pacific Meridional Mode in the winter‐summer. Our results highlight the potential of seasonal climate forecasts to inform management of upwelling‐sensitive marine resources. Plain Language Summary: Upwelling—the process of drawing cold, nutrient rich ocean waters toward the surface—plays a vital role in supporting vibrant and diverse biological populations throughout the California Current System (CCS). Here, we assess whether four global climate models can forecast seasonal upwelling 1–12 months in advance. We show that for much of the year (winter through summer), models can predict anomalous upwelling intensity several months in advance. We also show that the models can predict the timing of the "spring transition" (i.e., the start of the upwelling season) for much of the CCS. The model skill is related to large‐scale climate modes, including the El Niño‐Southern Oscillation, the North Pacific Oscillation, and the Pacific Meridional Mode. These climate modes alter the strength of the surface winds along the U.S. west coast from winter‐summer, giving rise to predictable patterns of upwelling. Our results highlight the potential of seasonal climate forecasts to inform management of upwelling‐sensitive marine resources. Key Points: Global climate models skillfully predict upwelling in the California Current System in winter‐summerModels also skillfully predict timing of spring transitionWinter skill is linked to the El Niño‐Southern Oscillation and North Pacific Oscillation, summer skill with the Pacific Meridional Mode [ABSTRACT FROM AUTHOR]