Abstract: The research takes apples and apricots of Hebei province as examples, based on the temperature data of meteorological stations from 1974 to 2015, and calculates accumulated temperature of each region since January, to determine the three phenological periods that are susceptible to frost disasters every year: the starting and the ending of initial budding stage, flowering stage and young fruit stage. Then the research calculates the daily minimum temperature of three phenological periods at different return periods based on the Gumbel distribution, which reveals the dangerous intensity of frost disaster, and evaluates the risk of production reduction due to frost disasters according to the vulnerability curve of the three phenological periods (the yield reduction rate corresponding to the daily minimum temperature) constructed from relevant literature. Taking the once-in-a-hundred-year return period as an example, apples and apricots in northern Hebei province were more likely to be affected by frost during the young fruit period and flowering period. Zhangjiakou city was most affected during each phenological period, with an average yield reduction rate of 47.44%. Among different periods, the risk of flowering period was the highest, the yield was reduced by 59.79%, in the flowering period, the risk of yield reduction of apples and apricots in Chengde city was up to 51.42%, while in the southern region of Hebei province, Xingtai city was relatively special, with the highest yield reduction rate at the initial budding stage, reaching 37.91%. According to the above evaluation results, targeted enhancements at frost disaster monitoring and early warning in each phenological period in these areas can be made. Adjust the planting structure properly, and speed up the development of new environmentally friendly forest and fruit anti-low temperature protection technologies.

Key words: Frost, Risk assessment, Yield decrease, Phenological period, Fruits