We examined the spatiotemporal variation in diurnal temperature range (DTR) and discussed the reasons for the changes of DTR in China based on data from 479 weather stations from 1962 to 2011. Results showed that DTR decreased rapidly (0.291°C/decade) from 1962 to 1989 due to slightly decreased T_max and significantly increased T_min, but the decrease in DTR has stopped since 1990 as T_max and T_min kept pace with each other. During 1990–2011, DTR remained trendless, with slight increase in the 1990s and slight decrease after 2000. During the whole study period from 1962 to 2011, DTR decreased at a rate of 0.157°C/decade nationally. Spatially, decreases in DTR were greatest in Northeast China and lowest in Southwest China with a transect running from northeast to southwest showing the decreasing trends change from high to low. Seasonally, DTR decreases were greatest in winter and lowest in summer, and the magnitudes of decrease reduced from the north to south of China. The changes in DTR were closely correlated with changes in sunshine duration (SD) in China except the Tibetan Plateau, suggesting that SD decrease is an important contributor to the decrease of DTR through its influence on T_max. In addition to the contribution of SD decrease, the increasing of precipitation played an important role in DTR decrease in Northwest China, the most arid region of China. It appeared that changes of cloud cover (CC) were not the reasons for DTR changes in the past 50 years as CC has decreased during the study period.

Reduction in vegetation cover caused by human activities has a great impact on soil temperature. It is important to assess how soil temperature responds to reduction of vegetation height and density. In this paper we first report the trends of mean annual soil surface and air temperatures recorded at the meteorological stations near the Ecological Research Station for Grassland Farming (ERSGF) from 1961 to 2007, then we setup an experiment using reed (Phragmites australis) stalks with different heights and densities to simulate effects of different vegetation height and density on soil and air temperatures. The warming rates of the mean annual soil and air temperatures were 0.043 and 0.041°C a⁻¹, respectively. Changes of soil temperature were characterized by both increased mean annual maximum and minimum soil temperatures. At the experimental site, mean daily temperature, mean daily maximum soil and air temperatures increased significantly. In contrast, mean daily minimum soil temperature increased significantly while mean daily minimum air temperature decreased significantly as the height and density of reed stalks reduced during the experimental period. Mean diurnal soil temperature ranges were smaller than mean diurnal air temperature ranges. These results highlight that the importance of vegetation cover on soil and air temperatures.