Winter chill is expected to decrease in many mild-winter regions under future climatic conditions. Reliable es timates of the chill requirements (CR) of fruit trees are essential for assessing the current suitability of cultivars and potential climate change impacts on fruit production. We determined chill and heat requirements of ten apple cultivars in northwestern Spain using a bud-forcing method. CR ranged from 59 (‘Granny Smith’) to 90 (‘Regona’) Chill Portions (CP) according to the Dynamic Model. These results indicate that international dessert apple cultivars such as ‘Elstar’ and ‘Granny Smith’ have clearly lower CR than the studied local cultivars. The agro-climatic needs of the traditional apple cultivars are aligned with the historical climate conditions in the region. To assess future apple cultivation in northwestern Spain, we evaluated winter chill availability over the course of the twenty-first century by applying an ensemble of future climate scenarios. Relative to the past, projected winter chill might decline by between 9 and 12 CP under an intermediate global warming scenario and by between 9 and 24 CP under a pessimistic scenario. Despite relatively minor changes, the viability of some local apple cultivars may be jeopardized by their high CR. Results suggest that even a moderate decline in future winter chill, relative to fairly high levels observed in the past, can threaten the economic sustainability of fruit tree orchards composed of high-chill genotypes. Strategies such as growing low- to moderate-chill cultivars may be critical for sustaining future apple production in the region. Our findings can help guide new breeding strategies aiming to develop climate-resilient cultivars adapted to future environmental conditions.