Acta Geographica Sinica ›› 2023, Vol. 78 ›› Issue (3): 587-603.doi: 10.11821/dlxb202303006

• Original article • Previous Articles     Next Articles

Spatio-temporal variation patterns of diurnal freeze-thaw cycles of the near-surface soil on the Qinghai-Tibet Plateau between 2002 and 2020

SHEN Qikai(), LIU Xiuguo, ZHOU Xin, ZHANG Zhengjia, CHEN Qihao()   

  1. School of Geography and Information Engineering, China University of Geosciences (Wuhan), Wuhan 430074, China
  • Received:2022-05-30 Revised:2023-02-17 Online:2023-03-25 Published:2023-03-27
  • Contact: CHEN Qihao E-mail:cugxgsqk@cug.edu.cn;cugcqh@163.com
  • Supported by:
    National Natural Science Foundation of China(41801348);National Natural Science Foundation of China(41771467)

Abstract:

The diurnal freeze-thaw cycle of near-surface soils on the Qinghai-Tibet Plateau (QTP) significantly affects the exchange of water and energy between the soil and the atmosphere, which is important for an understanding of the response of the QTP to climate change. Based on MODIS, AMSR-E and AMSR-2 data, we first obtained the diurnal calibration coefficients from AMSR-2 to AMSR-E in the Qinghai-Tibet Plateau (QTP), and then used the Fourier nonlinear model to fusion diurnal freeze-thaw index with surface temperature, and further obtained the diurnal freeze-thaw condition of near-surface soils at 1 km resolution per day, and finally carried out a study on the spatial and temporal changes of diurnal freeze-thaw cycles of near-surface soils in the QTP between 2002 and 2020. The results indicate that: (1) The improved calibration method of AMSR series sensors in this paper is more suitable for the QTP region than the calibration method for global scale. The accuracy of the freeze-thaw product obtained by fusion using the Fourier nonlinear model was 80.96% for diurnal freeze-thaw discrimination, which was 3.95% higher than that of the unfused product. (2) The frequency of diurnal freeze-thaw cycles in the seasonal freeze-thaw process of near-surface soils on the QTP varies spatially, with the highest frequency occurring in the southern Tibetan region and the Qinghai plateau, and is cyclical in time, the high frequency region shows a shift to the northwest when warming and to the southeast when cooling. (3) In the past 20 years, the trend of diurnal freeze-thaw days in different parts of the QTP is varied, with the northern Tibetan plateau, southern Tibetan alpine region and eastern Tibetan region showing an increase and the Qinghai plateau showing a decrease. (4) There are regional differences in the beginning of the continuous diurnal freeze-thaw cycle on the QTP, with the beginning of the thawing process being gradually delayed from east to west and the beginning of the freezing process being gradually delayed from west to east. In the past 20 years, the starting time of continuous diurnal freeze-thaw cycle in near-surface soils has been changing, with 0.17 d/a earlier during thawing and 0.18 d/a earlier during freezing.

Key words: Qinghai-Tibet Plateau, diurnal freeze-thaw cycles, near-surface soil, multi-source remote sensing, AMSR, MODIS