Abstract:

This study is based on the phenological data of Zhaotong apple from 2010 to 2023, the meteorological data and drought disaster data of Zhaotong from 1960 to 2023, and divided the phenologicals into six growth stages, including dormancy, bud, anthesis, fruitlet, expansion and harvest stage, and used the crop water deficit abnormal index (CWDIa) to analyze the drought frequency and duration of each growth stage, used the cumulative drought intensity (CDI) to identify the drought risk intensity, used the Morlet complex continuous wavelet transform(CCWT) to explore the time−frequency evolution characteristics of cumulative drought intensity, so as to analyze the occurrence law of drought risk in Zhaotong apple. The results showed that drought in the apple growing region of Zhaotong was characterized by a pattern of frequency, seasonality, suddenness, severity and sub−seasonality. The drought in each development stage followed as: there was a large difference in the frequency of occurrence, fruitlet (55y)>harvest and dormancy (49y)> anthesis (20y)> bud(19y)> expansion(8y), and the extreme drought were most likely to occur at the end of the fruiting period and during late harvests. The duration of drought was between 1−4 ten−days, and there were significant differences in CDI, with the mean of fruitlet(335.0%)>dormancy (172.7%)>bud(137.7%)>harvest(137.1%)>anthesis(68.1%)>expansion(8.0%). The thresholds for the classification and identification of drought risk intensity were different, sensitivity to drought stress of stage was expansion>anthesis>harvest> fruitlet>bud>dormancy. The risk of severe drought disasters was seasonal and the fruitlet>bud>harvest>expansion>anthesis>dormancy. Drought risk had shown multi-scale periodic, phased and abrupt changes, with a general trend of increasing drought risk since 1991. 

Key words: Apple, CDI, Drought risk, Discriminant thresholds, Wavelet analysis