Climate change reduces frost exposure for high-value California orchard crops

Authors: PARKER, LAUREN - University Of California, Davis; PATHAK, TAPAN - University Of California; Ostoja, Steven

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2020
Publication Date: 12/1/2020
Citation: Parker, L., Pathak, T., Ostoja, S.M. 2020. Climate change reduces frost exposure for high-value California orchard crops. Science of the Total Environment. 762. Article 143971. https://doi.org/10.1016/j.scitotenv.2020.143971.
DOI: https://doi.org/10.1016/j.scitotenv.2020.143971

Interpretive Summary: Here we show that climate change projections result in a decline in frost exposure across California, and that future frost risk will be lower for some of California’s most frost-sensitive high-value perennial crops. Additionally, we show that projected changes in frost exposure may result in tens of thousands of acre feet of water and millions in energy costs saved across California orchards but that reductions in risk are both crop and location specific. Through examining these changes to exposure during extreme frost years, and through detailing the implications of frost exposure changes for three illustrative high-value orchard crops, we highlight one potential benefit for agricultural production from climate change. However, the interactions of this benefit with the potential tradeoffs such as reduced chill, increased pest pressure, and greater potential for heat damages remains to be fully explored. Further, we reiterate that frost risk estimates for a given crop can be highly dependent on methodology, including the capacity to model plant physiology, phenology, and the conditions that result in frost damages (Darbyshire et al., 2016). These important lingering questions highlight the need for further and more comprehensive study to better provide growers with clear, actionable knowledge for improved, wholistic, and climate-informed decision making. Still, quantifying changes in cool-season exposure to frost temperatures does provide useful projections of climate change impacts to a critical agroclimatic metric, and this information may prove helpful for growers and farm managers in their decision making today, and provide insight for long-term orchard management planning in light of projected climate change.

Technical Abstract: Frost exposure is a particular challenge for cultivating perennial crops, whose adaptive capacity to weather and climate impacts is limited. Irrigation is a common means of mitigating damage, but draws on limited water resources, is costly, and energy intensive. Here we examined the projected impact of climate change on the incidence of frost temperatures during the coldest winters, defined by the 98th percentile of cool season (November–April) frost hours, under both early- and mid-21st century time periods, as compared to contemporary conditions, across a range of threshold temperatures. We focused on three high-value perennial orchard crops – almonds, avocados, and oranges – to assess the effects of climate change on the incidence of temperatures below crop-specific threshold temperatures and for crop-specific critical development phases, and what these temporal changes in frost exposure may mean for the water and energy requirements for mitigating damages. Across time periods and temperature thresholds, frost exposure declines in California's agricultural regions, with an average of reduction in frost exposure of 63% by the mid-21st century. The majority of almond and orange acreage saw 50–75% reductions in frost exposure by mid-century, while avocado acreage experienced >75% fewer frost hours. This yielded attendant reductions in water use and energy costs, and growers in the highest acreage counties may save more than 50,000 acre feet of water and $4.2 million in electricity costs for water pumping per year, collectively. Although climate change is projected to increase growing season crop water demands, pest pressures, and have an overall net-negative impact on agriculture, the potential reduction in frost exposure and the accompanying water and energy costs to mitigate frost damages may allow growers to reprioritize some of their long-term decisions around farm management.