Observed Changes Of Shallow Soil Temperatures Associated With Climate Factors In Northeast China

Soil temperature is an important indicator of climate change, the change of soil temperature will not only change the regional climate conditions, but also have some impact to large-scale circulation. Soil temperature is also one of the main physical properties at the same time, in addition to the influence of seed germination, seedling and root growth and development, also the plants absorb nutrients and moisture transport, such as the change of the available nutrients in the soil. Therefore, it is particularly important to analysis the changes of soil temperature and its relationship with other meteorological factors, also for geothermal response to climate change and provides a scientific basis for long-term forecast. Northeast area is located in the high latitudes northern hemisphere, the highest latitude in our country, belongs to the temperate zone monsoon climate, which is a sensitive area of climatic change. We select 31 sites in the northeast for the period of 1960 to 2007 during growing season,0,5, 10,15 and 20 cm daily mean soil temperature, air temperature, precipitation and sunshine duration data, using correlation and regression analysis method in order to reveal the change characteristic of soil temperature in northeast China, explore the relationship with air temperature, precipitation and sunshine duration. Results show that in the whole northeast area, the average soil temperatures at 0,5,10,15,20 cm were higher than the average air temperature by 3.6°,1.9°,1.4°,0.9° and 0.4℃, respectively. The distribution of soil temperature is similar to air temperature, both increasing from northeast to southwest. From May to August, soil heat conduction downward, in September, the direction of the heat conduction reversal. In northeast China, during the whole growing season, air temperature and various layers of soil temperature changes with similar phase during growing season, but compared with the air temperature,5,10,15,20cm soil temperature lag by 2,6,8,10 days, respectively. By calculating the relative dryer 20 years and wetter 20 years, the wet soil has a bigger conductive rate, it is concluded that the rainfall is main factors affect the geothermal heat conduction among the layers in the Northeast of China. Throughout the study period, the various of layer soil temperature rate increase from 0.309 to 0.367℃/10 y, were higher than the air temperature rate, overall, the increase of rate performance 0cm> 20 cm>15 cm> 10 cm >5 cm>air temperature, compare the differences between each layer, the difference between 0cm and 5cm biggest and from 5 to 20cm along with the increasing of depth the gradient between adjacent layer become very gentle. During the analysis period, air temperature and soil temperature increase abruptly around the year 1992, then maintained steady until 2000. Whatever during the growing season or every month, land surface temperature and the air temperature generally changes consistent, and in the same phase, but they show some differences, especially the late 90s. Air temperature and ground temperature were positively related, and at 5cm the correlation is strongest among the layers, sunshine duration and soil temperature in each layer were positively correlated, but not significantly, while the precipitation and soil temperature negative correlation, and show the correlation between surface temperature is strongest. Overall, beside air temperature, precipitation plays an important role in the changing soil temperatures during the growing season in Northeast China.