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Spatial and temporal variations of surface soil freezing days in Chang Tang Natural Reserve of Tibet during 1981-2018.

DU Jun1*, ZHOU Kan-she2, Ciwangdunzhu2   

  1. (1Tibet Institute of Plateau Atmospheric and Environmental Science Research, Lhasa 850001, China; 2Tibet Autonomous Region Climate Centre, Lhasa 850001, China).
  • Online:2020-04-10 Published:2020-04-10

Abstract: The nearsurface soil freezing/thawing status is an important indicator of climate change. Based on the daily minimum surface soil temperature and air temperature data in the period 1981-2018 from five meteorological stations in Chang Tang Natural Reserve of Tibet (CTNRT), the spatiotemporal distribution of the number of freezing days for the ground surface under the scenarios of 1.5 ℃ and 2 ℃ warming were analyzed with the methods of linear regression method and MannKendall test. The results showed that: (1) In the past 38 years, the first date of nearsurface soil freeze had been significantly postponed at a rate of 7.72 d·10 a-1, and the last date of nearsurface freeze had been advanced at a rate of 8.17 d·10 a-1. The duration days and freeze days exhibited declining trends, with a rate of 14.69 and 11.19 d·10 a-1,respectively. The average rate of change for most near-surface freezing variables in CTNRT was generally higher than that over the Qinghai-Tibet Plateau. (2) In terms of inter-decadal variation, the first date had been delayed, as opposed to the advanced last date, while the duration days and freeze days had been shortened in CTNRT. (3) The trend reversal for the near-surface freeze parameters occurred in the early 21st century, with the abrupt point being later than thatover Qinghai Tibet Plateau. (4) The values of near-surface freeze parameters in CTNRT are similar under theRCP4.5/RCP8.5 scenarios of 1.5 ℃ warming: the first date is delayed by 25 days, the last date becomes earlier by 22 days, and the duration and freeze days are shortened by 46 and 28 days, respectively. Under the RCP4.5/RCP8.5 scenarios of 2.0 ℃ warming, the first date is postponed by 35 and 33 d, the last date is advanced by 30 and 29 d, the duration is shortened by 64 and 62 d, and the number of days is reduced by 40 and 39 d.