Observed changes in shallow soil temperatures in Northeast China, 1960-2007

ABSTRACT: Soil temperature, an important indicator of climate change, affects ecological and biogeochemical processes above and below the soil surface. We analyzed changes in soil temperature at depths to 20 cm during the growing season (May to September) from 1960 to 2007 at 31 sites in Northeast China. We also analyzed air temperature, sunshine duration and precipitation records for trends and correlations with soil temperatures. In Northeast China, soil temperatures were higher than air temperatures at all depths; at depths of 0, 5, 10, 15 and 20 cm, average soil temperatures were higher than the air temperature by 3.6, 1.9, 1.4, 0.9 and 0.4°C, respectively. Like air temperature, regional average soil temperature changed little before 1992 but increased at all depths from 1993 to 2007; the rate of change ranged from 0.81 to 1.00°C decade^-1, faster than air temperature. There was significant warming at all depths only in the months of August and September. Change in soil temperature is mainly controlled by the combined impact of changes in air temperature and precipitation; soil temperature at 5 cm displayed the highest correlation with air temperature, while precipitation showed the strongest influence on the surface (0 cm) soil temperature.