ORIGINAL PAPER Potential vulnerability of Moroccan apple orchard to climate change–induced phenological perturbations: effects on yields and fruit quality Adnane El Yaacoubi 1 & Nabil El Jaouhari 2,3 & Mohamed Bourioug 3 & Lahcen El Youssfi 1 & Sanâa Cherroud 1 & Rachid Bouabid 3 & Mohamed Chaoui 2 & Aziz Abouabdillah 3 Received: 28 July 2019 /Revised: 10 October 2019 /Accepted: 19 October 2019 # ISB 2019 Abstract Climatic factors are of a big importance for the determination of phenological stages of several fruit tree species, including apple, during the pre- and post-blooming periods causing their modifications and consequently affecting the fruit quality and produc- tivity. This study aimed to identify the important dormancy phases (chilling and forcing periods) involved in determination of the flowering time in Gala apple trees in order to estimate temperature and chill/heat requirements, useful to assess the effect of climatic factors and phenological modifications on apple productivity and quality. Phenological and climatic data (temperatures, rainfall, irrigation, chilling and heat requirements) were collected, calculated, and measured from orchard in Imouzzer-Kandar, Morocco. Fruit productivity and quality parameters (total yield, fruit weight, size, firmness, and sweetness) were measured. Results showed a prolonged chilling period basing on the pre-blooming phases identified using partial least squares regression. Inadequate chill during warm seasons (insufficient chilling requirements) induces some phenological perturbations: late flowering, extended flowering duration, and period from flowering to harvesting. These phenological anomalies affect negatively the fruit quality of apple as a cause of inadequate climatic factors, mainly temperature and chilling requirements during the chilling period. Our findings demonstrated that sufficient chilling and heat requirements correlate positively with fruit weight, size, and firmness, although the low irrigation applied during the period from flowering to the harvesting times. In unfavorable conditions, total yield and fruit sweetness could be improved by supplementary irrigation during the same period. Practically, chilling requirements of 645–677 chill hours, 709–1157 chill units, and 43.4–55.2 chill portions according to 0–7 °C, Utah model, and Dynamic model respectively and heat requirements of 26,290–27,057 growing degree hours are sufficient for good fruit quality. These are equivalent to temperature of 9.3–9.9 °C during the chilling period and 11.1–12.5 °C during the forcing period. These findings are useful for eventual management measures in order to improve apple production in their cropping area. At long terms, we propose necessity of rearrangement of high-chill apple varieties by low-chill cultivars as a way of apple crop adaptation to climate variations. Keywords Climate variation . Apple . Phenology . Fruit quality . Yield . Chilling and heat requirements Introduction Pre-blooming periods in forest and fruit tree species, including apple trees, are still complicated phenological stages. Their progress takes place in ambiguous phases, controlled by some metabolic and genetic mechanisms in response to certain en- vironmental conditions (Heide 1993; Chmielewski and Rötzer 2001; Labuschagné et al. 2002). Apple production takes an important place in Moroccan gross domestic product (GDP). Royal Gala variety is largely planted in their cropping areas such as Imouzzer-Kandar. Knowing the dormancy pattern for this cultivar in this area would have a positive impact, since it Adnane El Yaacoubi and Nabil El Jaouhari contributed equally to this work. * Adnane El Yaacoubi a.elyaacoubi@usms.ma 1 Higher School of Technology Khenifra, University Sultan Moulay Slimane, PB 170, Khenifra, Morocco 2 Faculté des Sciences, Université Moulay Ismail, B.P. 11201, Zitoune, Meknès, Morocco 3 Départment d’Agronomie et d’Amélioration des Plantes, Ecole Nationale d’Agriculture de Meknès, km. 10, Route Haj Kaddour, B.P. S/40, 50001 Meknès, Morocco International Journal of Biometeorology https://doi.org/10.1007/s00484-019-01821-y