Abstract: Shaanxi has large apple cultivation areas and high apple yields, but its yields are susceptible to late frost. The occurrence of freezing damage is closely related to the apple flowering date and the time of late frost. Therefore, accurate prediction of apple flowering date and research on the temporal and spatial changes of apple flowering date is of great significance to the disaster prevention and mitigation of apple production. In this study, the phenological models (e.g. Spring warming model, Sequential model, Overlap model, and Parallel model) were used to study the variations of apple flowering date (including both first flowering date and end flowering date) in Shaanxi Province under the background of climate change. Firstly, four phenological models were selected to evaluate the results of model simulation on apple flowering date in Shaanxi apple producing areas, and the optimal flowering prediction models in the study area needed to be screened out. Then, based on the selected optimal model, the apple flowering date of each representative station (e.g. Luochuan, Baishui, Fengxiang, and Changwu) during the historical period (1980−2019) was simulated. Finally, based on the future meteorological datasets generated by 33 Global Climate Models (GCMs), the selected model was used to simulate the apple flowering date at each representative station from 2021 to 2100 under the two scenarios of RCP4.5 and RCP8.5, and the temporal and spatial variations of flowering date were analyzed. The results showed that the Sequential model was the optimal model to simulate the apple flowering dates in the Eastern and Western area of Weibei, while the Parallel model was the optimal model for Yan'an and the Western area of Guanzhong. From 1980 to 2019, the first flowering date of representative stations was advanced by 3.4−4.7d·10y−1, and the end flowering date of representative stations was advanced 3.3−4.6d·10y−1. The apple flowering date in the study area was gradually delayed from southeast to northwest, and the average annual flowering duration was about 10−11 days. Under the RCP4.5 scenario, the advanced rate of first and end flowering date was 0.7−0.9d·10y−1 and 0.6−0.8d·10y−1 at representative stations from 2021 to 2100. Compared with 1980−2019, the average first and end flowering date for 2021 to 2060 were advanced 0−4.4 days and 0−5.0 days at representative stations, and the average first and end flowering date for 2061 to 2100 were advanced 3.4−7.6 days and 2.6−8.2 days at representative stations. Under the RCP8.5 scenario, the advanced rate of first and end flowering date were 1.3−1.8d·10y−1 and 1.3−1.6d·10y−1 at representative stations from 2021 to 2100. Compared with 1980−2019, the average first and end flowering date for 2021 to 2060 were advanced 1.3−5.9 days and 1.0−6.1 days at representative stations, and the average first and end flowering date for 2061 to 2100 were advanced 6.7−12.4 days and 6.2−12.3 days at representative stations. Under future climatic conditions, the spatial distribution of apple flowering date was basically the same as the historical period, but the duration of flowering date was slightly shortened. For the first time, this study combined the flowering date prediction model with future climate datasets to study the apple flowering date variations in Shaanxi apple producing areas, and it will provide some theoretical basis for coping with the freezing damage in flowering dates caused by climate change in Shaanxi apple producing area.

Key words: Shaanxi apple, First flowering, End flowering, Frost, Flowering prediction model, Climate change