Viability of temperate fruit tree varieties in Spain under climate change according to chilling accumulation

Fruit trees stop their growth over the coldest period of the year to avoid damage. To resume their growth and for successful fruit production, they need to accumulate winter chill. It is expected that global warming will diminish winter chill availability with potentially negative impacts on the viability and yield of these crops. The objective of this study was to assess the viability of seven tree crops among the most relevant in peninsular Spain and the Balearic Islands. For this purpose, chilling requirements were gathered from the literature to define a requirement range for each tree crop encompassing most of the varieties used in Spain. Then the bias-adjusted outputs of an ensemble of 10 regional climate models under the two representative concentration pathways (RCPs), 4.5 and 8.5, were used to feed a chilling model for calculating chill accumulation. The ensemble's outcome agreement index was applied to each combination of chill requirement and climate ensemble to assess crop viability. This was done by testing the hypothesis that the winter chill accumulation will be greater than the safe winter chill for the 2021–2050 (near future) and 2071–2100 (far future) periods and for both RCPs. A future reduction in the safe winter chill areas is projected with high agreement in climate projections across peninsular Spain and the Balearic Islands independently of the RCP or future period. The crops studied would be viable in the near future period as long as varieties with low chilling requirements are used. These varieties, however, would not be adequate in the far future in some currently highly productive regions, where the situation would become more severe, especially under the RCP8.5 scenario. In these cases, adaptation would be possible by shifting the crop to adjacent areas together with careful variety selection in terms of chilling requirements. The results indicate that the RCP8.5 scenario in the far future has an especially negative impact on the crops analysed, calling for resolute mitigation measures to guarantee tree crop production and food security. Recommendations for adaptation, with low uncertainty regarding climate projections, were included here, using actual tree varieties, thereby facilitating interpretation and on-field application for farmers and agricultural technicians.