Impacts of Global Warming on Southern California’s Winegrape Climate Suitability

Abstract:

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 past and future climate suitability for the cultivation of winegrape and potential global warming impacts to southern California’s winegrowing regions. High-resolution regional climate projections obtained with a physically-based climate model reveal that by mid-21st-century southern California’s winegrowing regions will become warmer and drier. Evaluation of winegrape climatic suitability through several bioclimatic indices calculated between a historic climate period 1983‒2012 and a future period 2021‒2050 indicates increases in heat accumulation for all major winegrowing areas. Results indicate an average increase of about 10% in growing-degree day index for viticulture, while morning low temperatures in September may experience increases of approximately 11% in the future, impacting the ripening stage of grapevines and leading to changes in wine composition and quality. By 2050, areal extent of regions across all indices will reduce nearly 42% for the cool to warm climate suitability categories. Simulations also suggest decreases in annual precipitation of approximately 11% in the south, south central, and north central regions of the study area, which could further negatively affect the crop. 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. The projected decline in viticulture suitability highlights the need for adaptive capacity within this sector to mitigate the impacts of global warming.