Gaoyuan qixiang (Feb 2022)
Characteristic Analysis of the Spatio-temporal Distribution of Key Variables during the Soil Freeze-thaw Process over the Qinghai-Xizang Plateau
Abstract
The freeze-thaw process is one of the most prominent features of the land surface process on the Qinghai-Xizang Plateau， and quantifying the variation of the key variables that denote the soil freeze-thaw process has scientific significance for understanding the climate change， hydrological processes and ecosystems of the Qinghai-Tibetan Plateau.By using the ECMWF/ERA5 （European Centre for Medium-Range Weather Forecasts/ERA5） reanalyzed soil temperature， volumetric soil water and air temperature data， the temporal and spatial trends of the start date of soil freezing， the start date of soil thawing and the duration of the soil freezing and their relationships with the air temperature and altitude were investigated by using linear regression， Mann-Kendall test， moving t test and correlation analysis.These results demonstrated that the spatial distribution of soil freeze-thaw process in the Qinghai-Xizang Plateau is characterized by a trend of delaying freeze， advancing thaw and shortening freeze from the northwest to the southeast.The soil freeze-thaw process varied significantly on the Qinghai-Xizang Plateau from 1979 to 2018.The start date of soil freezing was delayed by 14.0 days with a rate of 0.17 d·a-1， and the start date of soil thawing was advanced by 11.0 days with a rate of 0.07 d·a-1， and the duration of the soil freeze was shortened by 25.0 days with a rate of 0.23 d·a-1 over the past 40 years.The overall trend of soil freeze-thaw process is the same in the Qinghai-Xizang Plateau， while the local rate is different.Throughout the period of study， the duration of the soil freeze in the southern and the northern Changtang Plateau is shortened by 47.2 days and 32.9 days.The first date of the soil freeze， the first date of the soil thaw and the duration of the soil freeze are significantly correlated with temperature and altitude.If the air temperature rises by 1.0 ℃， the first date of the soil freeze will be delayed by 5.2 days， and the first date of the soil thaw will be advanced by 4.5 days， so that the duration of the soil freeze will be shortened by 9.8 days.In the high cold Tibetan climatological zone， the first date of the soil freeze will be advanced by 9.1 days， and the first date of the soil thaw will be delayed by 4.9 days， while the duration of the soil freeze will be increased by 13.9 days as the altitude increases by 1000.0 m.
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