Abstract:

Based on the daily maximum temperature data at Urumqi meteorological station, we established the database of temperature-rising process of Urumqi city during the period of January 1 1951 to December 31 2015. A comprehensive strength index IZ was defined in terms of the intensity values and ranks of the temperature-rising process, and sorted the extreme temperature-rising processes in Urumqi according to IZ index percentile ranking. Thus, the change characteristics of the process sustained days, frequency and intensity were analyzed. The results showed that there were a total of 567 extreme temperature-rising processes in Urumqi during 1951-2015, and the average was 8.7 times per year. The maximum strength of the extreme temperature-rising process occurred in March 14-16, 2009. The average of sustained days was 3.25 d, and the number of sustained 2 d process was the most, accounting for 23.1% of the 567 extreme temperature-rising processes in Urumqi. The longest sustained days of extreme temperature-rising process was in April (5.37 d), and the shortest was in January (2.29 d) and December (2.37 d) during 1951-2015. The annual sustained days of extreme temperature-rising processes decreased slightly, and the linear trend was not significant in the past 65 years. The extreme temperature-rising process was mainly concentrated in the period of December?April, accounting for 64.3%, and the least was only 1.9% in July of Urumqi. In the past 65 years, the frequency of extreme temperature-rising process was not significantly increased linearly, more than mean frequency after 1980s and increased in the beginning of 2010s of the inter-annual variability of frequency. Both the intensity and its inter-annual variability of extreme temperature-rising process were more than the average in 1950s and 1960s in Urumqi. The intensity gradually was weakened, and the inter-annual variability was decreased from 1970s to 2010s. Both the intensity and its inter-annual variability were increased by the beginning of 21 century.

Key words: extreme temperature-rising process, frequency, intensity, change characteristics, Urumqi city