Abstract: Ground temperature is an important component in earth-atmosphere system. Understanding the changes in ground temperature is of great significance for deepening knowledge of climate change and ecosystem adaptation to climate change. The spatial-temporal variations in ground temperature at the depth of 0 cm were explored in 10 regions across China during 1961-2020, especially for up -to-date climatic baseline period of 1991-2020, by using linear trend and Cramér-von Mises methods based on daily observations from 640 meteorological stations. During 1961-2020, the average increment of ground temperature at the depth of 0 cm for yearly, spring, summer, autumn and winter was 0.41, 0.42, 0.16, 0.34 and 0.70 ℃·(10 a)^-1, respectively. The average increment in 1991-2020 relative to 1961-1990 was 0.52-2.12 ℃. Yearly and seasonal average ground temperature at the depth of 0 cm decreased from south to north. Only a few stations observed obvious increasing trend during 1961-1990, while most stations showed an obvious increasing trend during 1991-2020, and the increasing rate in northern areas was greater than that in southern areas. Regional increment of average ground temperature at the depth of 0 cm in 1991-2020 relative to 1961-1990 was 0.23-2.16, 0.24-2.18, -0.21-1.69, 0.18-1.52 and 0.20-4.35 ℃ for yearly, spring, summer, autumn and winter, respectively. When comparing across different regions, the increment of average ground temperature was larger in Northeast China, Inner Mongolia and Xinjiang, which was larger in winter and smaller in summer. The increasing trend of yearly and seasonal average ground temperature at the depth of 0 cm was not obvious in most regions during 1961-1990, but showed an increasing trend during 1991-2020. The increasing rate of average ground temperature at the depth of 0 cm was the greatest in winter, followed by spring, autumn, and summer. Moreover, the abrupt change years of significant difference of annual and seasonal ground temperature were generally after 1991.

Key words: ground temperature at the depth of 0 cm, spatial-temporal variation, climatological reference time, meteorological geographical division.