Freeze-Thaw Characteristics of Seasonally Frozen Ground in the Three River Source Region from 1961 to 2020

Abstract

Based on the data of daily maximum freezing depth of the seasonally frozen ground， near surface air temperature and precipitation from 21 meteorological stations in the three river source region during 1961 to 2020， by using mathematical statistics method， the spatial-temporal characteristics of freezing start date， thawing end date and annual maximum freezing depth of seasonally frozen ground and their relationship with air temperature and precipitation were analyzed.The results demonstrated that the freezing start date of seasonally frozen ground in the Three River Source region mostly occurred from late September to late October， and the thawing end date mostly occurred from April to May.During recent 60 years， the freezing start date of seasonally frozen ground in the Three River Source region was significantly delayed， and the thawing end date was significantly advanced， especially since 1990s.In the 21st century， especially in the past 10 years， the annual maximum freezing depth has decreased remarkably.The spatial distribution of freezing start date， thawing end date and annual maximum freezing depth of seasonally frozen soil in the Three River Source region was mainly linked to elevation.The freezing start date （the thawing end date） was gradually delayed （advanced） from high to low altitude， and the maximum freezing depth gradually decreased from high to low altitude.In recent 60 years， the warmer and wetter climate in the Three River Source region was linked to the delayed of the freezing start date， the advance of the thawing end date and the decrease of the annual maximum freezing depth.The average freezing start date and thawing end date were highly correlated with the temperature and precipitation in October and April， respectively， and the annual maximum freezing depth had the highest correlation with the temperature in January and the precipitation in August of the previous year.

Keywords

• the three river source region
• seasonally frozen ground
• climate change
• freeze-thaw characteristics