Frozen ground temperature trends associated with climate change in the Tibetan Plateau Three River Source Region from 1980 to 2014

Long-term (1981-2014) trends in soil temperatures at depths ranging from 0-320 cm were used to examine relationships between regional climate change and soil temperatures in the Three River Source Region (TRSR) of the Tibetan Plateau (TP). Air temperature, precipitation, maximum depth of frozen ground and maximum snow depth were also analysed for trends and for correlations with soil temperatures. A significant warming trend was evident in the TRSR during the 35 yr analysed. Significant soil warming was detected, at rates of 0.706 degrees C decade(-1) for surface soils (0 cm), 0.477 degrees C decade(-1) for shallow layer soils (5-20 cm) and 0.417 degrees C decade(-1) for deep layer soils (40-320 cm). There was a clear effect of air temperature on soil temperature, as seen from the concurrent significant increases in air and soil temperature trends and the strong cor relation between them. The relationship between precipitation and soil temperatures was com plicated. Higher levels of precipitation on the ground also resulted in higher soil temperatures during the summer in the frozen soil, while the process of freezing and thawing had an inhibitory effect on the soil temperature increase. The warming trends in soil temperature are expected to continue with the degradation of frozen soil in the TRSR.