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

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.