Abstract:Using observation data of monthly mean soil surface temperature, air temperature and annual sunshine hours, evaporation, precipitation, relative humidity, average wind speed from four meteorological stations in Wuwei city of Gansu Province during 1961-2010, the spatial and temporal distribution characteristics of the differences between soil and air temperature (Ts-Ta) were analyzed systematically by trend coefficient method, the main meteorological factors of (Ts-Ta) were also analyzed by correlation coefficient method and standardized regressive coefficient in multi-linear regression. The result showed that spatial distribution of (Ts-Ta) was related to the local factors as vegetation, soil stratum lithology, soil moisture; the maximum value (3.5 ℃) of (Ts-Ta) occurred in central oasis plains, minimum value (2.6 ℃) of (Ts-Ta) occurred in desertification of northern district. Monthly change characteristics of (Ts-Ta) was obvious and consistent relatively, whose variation rate was larger between 4.8 ℃ and -6.8 ℃, showed an obvious peak and trough, larger value occurred in the summer half year whose highest value was in June, smaller value occurred in the winter half year whose lowest value was in December. But seasonal trend was not consistent, which showed an upward trend in spring and summer, and rose in central-north area but decreased in the shallow mountain area in autumn, decreased in winter except northern desert area. Annual change showed overall upward trend, rising velocities of (Ts-Ta) were influenced by altitude and underlying surface, it rose the fastest in Gobi desert area, rapidly in Oasis plain region, and slowly in Qilian Mountains slope. The time series of mean annual (Ts-Ta) existed the quasi periodic variation of 5-7a, through a significant level of reliability α =0.05 (F test), and the mutation happened in 2004. Decadal change was very obvious, which was smaller from 1960's to 1970's and larger from 1980's to 2010's. Both of annual soil temperature and air temperature increased, presented an asymmetric change, annual (Ts-Ta) was positively correlated with soil temperature and air temperature whose direct cause was that the rising trend of soil temperature was more significant than that of air temperature. The variation of seasonal (Ts-Ta) was more closely related to variation of soil temperature, the rising trend of (Ts-Ta) was larger in the season that soil temperature increased significantly. The main influencing factors of (Ts-Ta) were maximum air temperature, evaporation and precipitation. (Ts-Ta) was positively correlated to average maximum soil temperature, average minimum air temperature and sunshine hours, but negatively correlated to evaporation, precipitation, relative humidity and average wind speed. Main influencing factors of (Ts-Ta) were different from different stations, which were maximum surface temperature, precipitation and evaporation in Liangzhou; minimum temperature, evaporation and maximum surface temperature in Minqin; maximum surface temperature, minimum temperature and relative humidity in Gulang; maximum surface temperature, relative humidity and minimum temperature in Yongchang. In the context of climate warming, to study and grasp the change rule and influencing factors of (Ts-Ta) was an essential part of revealing meteorological disaster pregnant environment and assessing regional climate evolution. At the same time, it provided scientific reference for curbing ecological environment deterioration, adjusting agricultural production and optimizing planting structure.
