Abstract:
Based on the daily minimum temperature data from 1991 to 2023 and the observation data of apple flowering period from 2001 to 2023 in Nyingchi meteorological station of Xizang, the daily minimum temperature was used as the frost index, and the linear tendency estimation and Mann-Kendall test were used to analyze the variation characteristics and climate risk index of late frost in Nyingchi during apple flowering period in recent 23 years (2001—2023). The results showed that: (1) In the past 33 years, the late frost date of each grade in Nyingchi showed an advancing trend, with a rate of 2.88~5.76 days per decade. The date of moderate late frost was the most early, especially in the past 23 years. There was no mutation for light frost, and the mutation time for medium and heavy frost appeared in 2020, 2004 and 2011, respectively. (2) In the past 23 year, the flowering period of apple in Nyingchi showed a significant delay trend, with a rate of 5.15~9.39 days per decade, which was most obvious at the beginning of the flowering period. The beginning, bloom and end date of the flowering period underwent a mutation from early to late in 2014, 2016 and 2010, respectively. (3) The frequency of light and moderate late frost during apple flowering period were 56.5% and 30.4% respectively, and no severe late frost was encountered. The climate risk index of late frost during apple flowering period was 1.17, which was significantly higher than that in Bohai Bay, Shaanzhou District of Loess Plateau, and Aksu of Xinjiang. In conclusion, the end date of late frost in Nyingchi tended to be earlier, the flowering period of apple delayed significantly, and the climate risk of late frost in flowering period obviously reduced.