The spatiotemporal variations of soil water content and soil temperature and the influences of precipitation and air temperature at the daily, monthly, and annual timescales in China.

Soil water content (SWC) and soil temperature (ST) are important properties in water-energy balance processes. Our objective was to analyze the SWC and ST variations at different soil depths (0–10, 10–40, 40–100, and 100–200 cm) and different timescales (daily, monthly, and annual) affected by precipitation and air temperature at seven sub-regions and entire mainland China. The sine function was used to fit the variations of daily and monthly ST. The results showed that the monthly and annual SWC and ST values were relatively low in northwest China and the alpine region of Qinghai-Tibetan plateau; however, higher values were shown in east China. SWC and ST fluctuated both randomly and periodically, especially at the 0–10 cm depth. The daily and monthly ST had regular time-lags and typical periodical changes, which could be fitted by a sine function for both the grids and sub-regions in China with a coefficient of determination (R2) of 0.855. Further, the correlations between SWC and precipitation were good in southern and northeastern China, but poor in northwestern China and Qinghai-Tibet Plateau at the depths < 40 cm. The correlations between ST and AT within the depths < 100 cm were generally good (R2 > 0.76). In conclusion, the spatiotemporal distribution of SWC and ST was greatly affected by precipitation and air temperature. The fitted sine functions for daily and monthly ST are very useful for elementary determination of the long-term mean ST values for a location. [ABSTRACT FROM AUTHOR]