Comprehensive Climatic Index and Grade Classification of Cold Damage for Taiwan Green Jujube in Fujian

Taiwan green jujube is widely planted in Fujian, Guangdong, Guangxi and Hainan because of its high planting efficiency. However, these areas locate in the northern edge of planting areas of tropical fruit trees, therefore blindly planting may aggravate the loss of cold damage. In order to achieve a reasonable distribution and reduce the loss of cold damage, it is urgent to establish objective and quantitative comprehensive climatic index for cold damage of Taiwan green jujube in these areas.The classification standard of cold damage symptoms is established by interview of experts and field disaster investigation. According to field observation and results of geographical transplantation experiment, combined with the investigation of cold damage from December 2014 to February 2015 and December 2015 to February 2016, 32 samples of cold damage are obtained, and the critical temperature of cold damage for Taiwan green jujube is determined to be 5.0℃. Referring to each process of the cold damage examples, the disaster grade of each cold damage example is obtained by comparing the classification standard of cold damage symptoms, and the correlation between meteorological factors and disaster grade is analyzed. The disaster-inducing factors for cold damage of Taiwan green jujube are determined, including the extreme minimum temperature, sustained days of cold damage process with the temperature below 5.0℃, the process of harmful cold accumulation for the extreme minimum daily temperature below 5.0℃, and the cooling range of cold damage process for the temperature below 5.0℃. After normalizing each factor, principal component analysis is used to simplify four disaster-inducing factors, and the comprehensive climatic index of cold damage for Taiwan green jujube is constructed. The formula is I_h=-1.255X₁+1.688X₂+0.53X₃+2.52X₄. K-means cluster analysis method is used to determine the index classification combined with the cold damage grade. The cold damage is graded with Ih as follows:0.02≤I_h < 0.72, light; 0.72≤I_h < 1.76, moderate; 1.76≤I_h < 2.72, severe; I_h≥2.72, most severe. According to the method of comparative validation for typical years, the comprehensive climatic grade index of cold damage for Taiwan green jujube is in good agreement with the actual situation, which verifies the reliability of the index. Results have practical reference value for the evaluation of cold damage, introduction and expansion of Taiwan green jujube.