The Freezing Damage of Citrus of Hubei Province in 1991 and the Division of Freezing-Avoiding Cultivation

By examining the relationship between decreasing rate of orange yield per unit area in 1992 and the minimum temperature in December 1992 in various regions of Hubei Province, it is found that there is an exponential correlation. So, the relationship between the freezing damage of citrus and the minimum temperature can well be explained. By using Gumbel distribution, the minimum temperature once every 5, 10, 20, 25 and 50 years are calculated for 59 stations. Furthermore, according to various minimum temperature once in a decade indifferent regions of Hubei Province, the area-division between optimum, sub-optimum and no-optimum for planting orange in Hubei Province is given. Therefore, the scientific basic for freezing-avoiding cultivation is provided.