| Using Tmin≤-1℃ as freezing index, by taking the information of freezing weather events of 27 major apple growing counties in Shaanxi Province form 1970～2008 as the background, fuzzy mathematics and information diffusion theory are applied to analyze quantitatively the risk level in different time and to ascertain the priority prevention time and flower thining time.The results indicate that in the whole 27 major apple growing counties, the risk probability in April is always greater than 80%, but is lower than 1/2 and 1/10 after Apr.10 and Apr.20.In addition, the end of key prevention time and initiation of safe flower thinning time are ascertained by using risk probability in 50% and 20% as index, both of which are postponed gradually form southeast to northwest. |