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Arid Land Geography ›› 2022, Vol. 45 ›› Issue (1): 103-112.doi: 10.12118/j.issn.1000–6060.2021.108

• Climate Change • Previous Articles     Next Articles

Variation characteristics and its influencing factors of the compound hot extremes at daytime and nighttime in Xi’an City based on MF-DFA

LI Shuangshuang1,2(),WANG Ting1,2   

  1. 1. School of Geography and Tourism, Shaanxi Normal University, Xi’an 710119, Shaanxi, China
    2. National Demonstration Center for Experimental Geography Education, Shaanxi Normal University, Xi’an 710119, Shaanxi, China
  • Received:2021-03-01 Revised:2021-04-22 Online:2022-01-25 Published:2022-01-21

Abstract:

Improving research methods and regional adaptation measures depend on the refining of extreme weather processes. However, it is still a great challenge to refine the types of historical warming to more sophisticated extreme events. We identified three summertime hot extremes based on daily temperature (Tmax and Tmin) data obtained from 22 meteorological stations in Xi’an City, Shaanxi Province, China and the surrounding areas: independent hot days, independent hot nights, and compound hot extremes. The stochastic resort detrended fluctuation analysis (MF-DFA) and extreme-point symmetric mode decomposition (ESMD) were used to determine the variation of the compound hot extremes during the day and night in Xi’an City from 1955 to 2019. Meanwhile, the influencing factors of the annual fluctuation of the compound hot extremes during the day and night were analyzed. The results show that: (1) the highest temperature and threshold of the original data are the same as the homogenized data in Xi’an City. The threshold of the lowest temperature is relatively lower by 0.2-0.5 ℃ after homogenization. As a result, the Xi’an station was relocated between urban areas and suburbs between 1959 and 2005, which resulted in an underestimation of the extreme temperature trend. (2) While the MF-DFA, 90.0%, and 95.0% threshold schemes perform similarly well in identifying high temperature events, the 99.0% threshold and relative threshold schemes are the primary sources of uncertainty. (3) The interannual fluctuation and trend changes from 3.3-3.8 a were the compound hot extremes from 1955 to 2019. The number of compound hot extremes increased significantly in the mid-1980s, while the normal number of days and independent hot days decreased, and the number of independent hot nights and compound hot extremes increased. (4) The sea surface temperature (SST) anomaly in the equatorial western Pacific Ocean can be used as a key sea area for early warning of Xi’an City’s day and night combined high temperatures. The circulation analysis of the day-night composite high temperature events lasting more than five days verified the reliability of the abnormal warming of SST in the equatorial western Pacific as early warning information. In addition, we found that the South Asian high is moving northward and the western Pacific subtropical high is extending westward, which is the specific circulation mechanism of the regional day-night composite high temperature. It is important to understand that the variation in characteristics of the compound hot extremes at day and night in Xi’an City from 1955—2019 and the circulation characteristics of hot extremes lasting more than five days. One could argue that this study establishes both a theoretical and methodological basis for urban climate adaptation.

Key words: climate change, the compound hot extremes at daytime and nighttime, El Niño, Xi’an City