Increased Risk of Cold Damage to Grapevines in spite of Warmer Temperatures: Importance of Considering Winter Season Dynamics.

Abstract:

Cold damage to grapevines is a primary production risk for the wine and grape juice industry, impacting yield and profitability in the current and subsequent years. However, climate change impact studies on viticulture have largely focused on growing season dynamics or made simplifying assumptions about winter season dynamics (e.g. assuming that average winter temperature exposures below a threshold lead to lethal cold damage and unsuitability for production). In the context of warmer future temperatures, such simplifying assumptions lead to currently unsuitable production regions modeled as potentially suitable in the future. Contrary to this intuitive expectation, warmer winters could lead to increased rather than reduced risk of cold damage. Hardiness thresholds (damage-inducing temperatures) develop as a result of dynamic processes that depend on temperature exposures. Consequently, while warming lowers the exposure to cold temperatures, it can also lead to higher cold hardiness thresholds (i.e., damage occurring at higher temperatures). The objective of our work is to consider the dynamic nature of cold hardiness development, and quantify the impacts of climate change on cold damage risk in grape production. We consider the US Pacific Northwest as a test case, use future climate projections (19 models each of RCPs 4.5 and 8.5) to drive a dynamic cold hardiness model for multiple varieties of grapes, and quantify changes in cold damage risk. Our results indicate an increase in cold damage risk in the near future. The risk diminishes as we go further out where the rise in temperatures compensate for a loss in hardiness. While there are geographic differences in results, in the near future (20 to 30 year investment horizon for producers), there are several regions with more than 20% absolute increase in the number of years with damaging events. Warmer fall and spring temperatures prolong the cold acclimation period, trigger unseasonal deacclimation, and accelerate spring deacclimation and budbreak phenology. This reduces the damage “safety margin” and increases vulnerability to bud damage. These results underscore the importance of considering winter season dynamics along with growing season dynamics to get a complete picture of climate change impacts on viticulture and other perennial crop industries.