Potential Effects of Weather, Climate and Climate Change on the California Winegrape Industry

Weather and climate are major considerations for the California winegrape and wine industry. Weather and climate directly affect winegrape characteristics and yield. Climate (expected weather) also affects vineyard management and production costs and thereby indirectly affects grape characteristics and yield. California is divided into seventeen crush or pricing districts. In 2011 the average price of Cabernet Sauvignon differed by up to a factor of ten across districts. Weather and climate vary across crush districts and explain part of this price variation. The effects of climate change on California winegrapes interest all those concerned with the evolution of land use and grapes production and prices. This dissertation estimates relationships among weather, climate, yield and sugar content of winegrapes grown in the seventeen crush districts in California. After an overview of the relevant biological and economic relationships, chapter 3 focuses on the recent climate and historical climate change in California winegrape crush districts. This dissertation uses eight decades of daily weather data from 86 weather stations across California to model and document climate conditions and historical climate change by crush district. Climate changed differentially across California crush districts and climate change in each region differs by weather variables. Unlike most studies that use downscaled projections from global climate models, this dissertation uses historical trends of weather to project climate for 2080. Using these trends, average growing season minimum temperatures in California winegrape regions would increase by 3–4.3°F by 2080, and average growing season maximum temperatures would increase by 0.2–0.8°F. Chapter 4 estimates statistical relationships among climate, weather, yield and sugar content by variety and crush district. Using historical vineyard data (rather than experimental data), vineyard management affects these estimates. The estimated historical relationships are used to project potential effects of climate change on yield and sugar content of winegrapes by variety and crush district for 2080. Average yield in California is expected to increase by 1.5–2.4 ton/acre and average sugar content of winegrapes grown in California is projected to decrease by 1.3–2 degree Brix, conditional on other variables