Future Winegrape Crop Suitability in Southern California and Winegrower's Perceptions of Climate Change Impacts

Southern California has seen a resurgence of winegrowing regions in the past few decades, however the future of winegrape climatic suitability in the area has not been exhaustively explored. This study evaluated the future climate suitability for the cultivation of winegrape and potential global warming impacts on southern California's winegrowing regions through a series of high-resolution surface air temperature and precipitation projections obtained with the WRF-SSIB regional climate model. Results reveal that by mid-21st-century the surface air temperature will increase by approximately 1.2 °C, while average precipitation will decrease by as much as 11% in the southern winegrowing areas under the Intergovernmental Panel on Climate Change high greenhouse-gas emissions scenario. Evaluation of bioclimatic suitability indices indicate increases in heat accumulation for all major winegrowing areas; including an increase of about 10% in growing-degree day, while morning low temperatures in September may experience increases of approximately 11% in the future, thus impacting negatively the ripening stage of grapevines and leading to changes in wine composition and quality. Additionally, the extent of areas classified under the cool to warm climate suitability categories could decrease by nearly 42% in the study area by 2050. Conditions in southern California are already warm and dry for viticulture and continuing heat accumulation increase, along with rainfall reduction, could potentially place additional stress to winegrape crop in the area, including advanced phenological timing and moisture deficit stress that could lead to decreases in yield. The projected decline in viticulture suitability highlights the need for adaptive capacity within this sector to mitigate the impacts of global warming. Possible mitigating strategies include planting hotter climate grape varieties, moving vineyards to regions that are more suitable in the future, and adopting dry-farming techniques. Despite potential declines to wine yield and quality, growers’ perceptions of climate change and their management response play a critical role in adaptive potential, but have not been well examined for southern California. We use a survey approach to better understand how winegrowers in the South Coast American Viticultural Area perceive climate and climate impacts, and if and how they are adapting on their vineyards. We further assess winegrower’s adaptive capacity based on knowledge and resource accessibility, as well as subjective feelings of preparedness to climate risks. We find that over the past decade many growers are observing fewer rain events (73%) and more frequent heat events (63%). This is followed by observed changes to vineyard phenology, particularly earlier bud burst (32%) and harvest dates (41%). Growers reported implementing a variety of short-term adaptive practices, such as canopy management, but fewer considered long-term anticipatory measures, such as planting drought/heat tolerant varieties. However, those who perceived negative impacts of climate change or regarded it as a threat were more likely to have implemented adaptive strategies (p = 0.02), and also reported feeling more prepared (p = 0.05). Despite some growers expressing confidence in overcoming climate challenges, many feel they do not have the necessary support (34%) or resources (52%) to do so. We identify a pressing need for participatory science that fosters cross collaboration and knowledge exchange between growers, academics, local government agencies, and appropriate stakeholders toward capacity building, which should promote the resilience of this burgeoning wine industry.