Changes in the permafrost temperatures from 2003 to 2015 in the Qinghai-Tibet Plateau

Alterations in the permafrost due to a warming climate increases the risk of permafrost thawing, accelerates carbon release, lowers super-permafrost groundwater, strengthens desertification, and destroys infrastructure. The permafrost temperature in six boreholes up to 40 m depth was measured from 2003 to 2015 along the Qinghai-Tibet Railway. Results showed an increase in the permafrost temperature, with an average of 0.14 degrees C decade(-1) at 10 m depth. The deep permafrost showed significant warming with average rates of 0.11 and 0.09 degrees C decade(-1) at 20 m and 30 m depth, respectively. At 40 m depth, the cold permafrost showed significant warming trend, but no evident warming trend was observed in the warm permafrost. With the ground temperature increases, the depth of the zero annual amplitude of the ground temperature of the warm permafrost slightly increased, whereas that of the cold permafrost decreased. Permafrost thickness was < 30 m at the BL1 and TT1 sites and was thinner by 2.1 and 0.8 m from 2003 to 2015. Such changes in the permafrost temperature may have been driven by the long-term increase in the air temperature and precipitation on the Qinghai-Tibet Plateau (QTP). In the high-middle mountain areas of the QTP, the thermal effect of warming climate on the cold permafrost reached a depth of > 40 m. In the high plain and basin of the QTP, the thermal effect of the warming climate on the warm permafrost reached a depth of 30 m.