Louis Delelee, Patricia Skinkis,* and A. John Woodill
*Oregon State University, 2750 SW Campus Way, Corvallis, OR, 97331
(patricia.skinkis@oregonstate.edu)

Climate change is a growing concern for winegrape production worldwide. One of the unknowns associated with climate change is the impact of increasing temperatures on grapevine physiology. Increased temperatures may affect the timing of key phenological stages during the growing season, thereby impacting final crop quantity and quality. The relationships between grapevine physiology and growing degree day accumulation have been studied using temperature-based phenological models. However, these models perform inconsistently among regions, especially when models that were calibrated in one pedo-climatic context are applied to other regions, where factors that limit grapevine growth differ. We used the Smoothed-Utah and Wang-Engel phenological models and the Grapevine Sugar Ripeness model, each of which was applied to observed phenological dates from 2012 to 2021 for 18 vineyards across the Willamette Valley. Model performance was assessed using Root Mean Squared Error (RMSE), model efficiency, and adjusted R-squared. The RMSE values ranged from 5.5 to 8.5 days and R-squared values from 0.35 to 0.56 for each phenology stage modeled. Calibrated models were then used to project phenological dates from 2020 to 2100 under four climate change scenarios as defined by the Intergovernmental Panel on Climate Change’s Shared Socioeconomic Pathways. High-emissions scenarios indicate that bloom, veraison, and harvest will occur anywhere from three to five weeks earlier in the growing season. Additionally, as veraison and harvest shift earlier, they will occur at warmer stages of the growing season. However, budbreak dates are less affected by increased temperatures under high-emissions scenarios. The lowest-emissions scenarios project all phenology dates will shift roughly one week earlier. These results represent a resource for Willamette Valley grapegrowers as they anticipate future challenges and make informed decisions to address them.

Funding Support: Northwest Center for Small Fruits Research, Oregon Wine Research Institute, Oregon State University Viticulture Extension