A variety-specific analysis of climate change effects on California winegrapes

Authors: PARKER, LAUREN - University Of California, Davis; ZHANG, NING - University Of California, Davis; ABATZOGLOU, JOHN - University Of California; KISEKKA, ISAYA - University Of California, Davis; McElrone, Andrew; Ostoja, Steven

Submitted to: International Journal of Biometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2024
Publication Date: 4/23/2024
Citation: Parker, L.E., Zhang, N., Abatzoglou, J.T., Kisekka, I., McElrone, A.J., Ostoja, S.M. 2024. A variety-specific analysis of climate change effects on California winegrapes. International Journal of Biometeorology. 68:1559-1571. https://doi.org/10.1007/s00484-024-02684-8.
DOI: https://doi.org/10.1007/s00484-024-02684-8

Interpretive Summary: California is the top winegrape producing state in the United States. However, climate change is projected to alter climate indicators important to viticulture and increase the incidence of conditions that are not favorable to winegrape production. Previous research has shown that the effects of climate change on winegrapes vary by location and grape variety, but a spatially explicit and variety-specific analysis has not been conducted in California. Therefore, this study explores the potential effects of projected climatic changes on winegrape production in California across 12 key viticultural regions and 6 grape varieties by modeling potential shifts in variety-specific phenology and quantifying the change in viticulturally-important climate metrics at the scale of American Viticulture Areas (AVAs). The study shows that winegrape development will shift towards earlier budburst, flowering, veraison, and maturity, but that how much earlier depends on the variety, the location, and the specific development phase. Likewise, the study shows that some AVAs will be more exposed to unfavorable conditions such as extreme heat days. The degree to which an AVA will experience changes in viticulturally important climate metrics similarly depends on the location and the metric in question. The results of this study are confirmatory and well aligned with the existing literature while the AVA-scale climate projections and projected phenology changes for California winegrapes provides variety-specific information at a meaningful spatial scale that can empower growers to identify and adopt the most appropriate adaptation actions for their situation. Moreover, the approachable methodology presented in this study can be applied to other varieties, crops, and/or geographies to support climate resilience in agriculture.

Technical Abstract: California contains a broad geography over which climate conditions can be suitable for cultivating many varieties of winegrapes. However, climate change is projected to make winegrape cultivation more challenging across many of California’s winegrowing regions. In order to understand the potential effects of climate change on winegrapes, this study models the potential shifts in variety-specific phenology for six winegrape varieties and quantifies the change in phenology and viticulturally-important climate metrics over 12 of California’s American Viticultural Areas (AVAs) by the mid-21st century. Results show a contracted growing season for winegrapes with earlier budburst, flowering, veraison, and maturation across all varieties and AVAs. Cabernet Sauvignon shows the greatest change in phenology timing, while Chardonnay shows the least change. Likewise, the West Sonoma Coast AVA shows the greatest average change in phenology timing across varieties and development stages and Lodi AVA shows the least. Projected changes in agroclimatic metrics include an additional month of potentially damaging heat days (above 35°C) in some AVAs, and decreases in frost days. These projected changes in phenology and agroclimatic metrics underscore the need for California winegrape growers to adopt strategies, such as shift grape varieties (plant heat-tolerant or drought-resistant grape varieties), change planting practices (adjust the timing of planting and pruning to match the changing growing seasons and temperature patterns), irrigation management (implement more efficient irrigation systems to conserve water and ensure consistent moisture levels), and adaptive harvesting (adapt the timing of grape harvest to account for changing ripening patterns), to improve their resilience to climate change. By conducting climate effects analyses at the variety-specific and AVA scale, important information is provided to the winegrowing industry at a resolution that can support decision-making towards resilience.