Soil moisture and temperature are both significant factors for crop growth and development. They are also the main influencing factors of regional climate change. In the context of climate change, the relationship between soil moisture and soil temperature is not only important for explaining the mechanism of moisture and temperature interaction, but also provides scientific suggestions for agricultural production. Since the accurate measurement of soil moisture and temperature is difficult, their relationship remains poorly understood. Here, based on real-time field observation in a potato field in Wuchuan County, Inner Mongolia, China, the change characteristics of soil moisture and temperature under different water level treatments were analyzed, and their relationships were disclosed. The results show that there was an inverse proportional relationship between soil moisture and temperature. With an increase of soil moisture, soil temperature decreased. The basic relation between soil moisture and temperature took the form of reciprocal functions (Q = 4.2 × 10³ V × (0.2 + W) × ΔT). The decline of soil moisture in the farmland will increase the soil temperature and has a negative impact on land–atmosphere interactions. The results can provide important insight into regional climate change mechanisms.

Soil moisture is closely related to the hydrosphere, atmosphere, and biosphere, which makes it one of the most significant climate variables. Using data from the National Environmental Forecasting Center (NCEP), this paper analyzes the temporal and spatial characteristics of soil moisture at a depth of 0–10 cm in China for the period of 1948 to 2014. In addition, the soil moisture’s possible interaction with air temperature is explored. Mainly using statistical analysis, the results showed that annual soil moisture decreased significantly (p < 0.01) in most areas. The tendency of decreasing soil moisture was relatively higher in spring and autumn than that in summer and winter. As to the national annual average soil moisture, there was a sudden change in the 1970s. The soil moisture had a relatively high value with a larger deviation before the abrupt change, but after that, the soil moisture was at a relatively low level with a smaller deviation. It was also found that the soil moisture at 0–10 cm showed a negative correlation with the 2-m air temperature above ground in the northern part of China, where the speed of the temperature rise was higher. The results are expected to help improve the understanding of the link between regional soil moisture variation and climate change.

Soil moisture is not only an essential component of the water cycle in terrestrial ecosystems but also a major influencing factor of regional climate. In the soil hydrothermal process, soil moisture has a significant regulating effect on surface temperature; it can drive surface temperature change by influencing the soil’s physical properties and the partitioning of the available surface energy. However, limited soil temperature and moisture observations restrict the previous studies of soil hydrothermal processes, and few models focus on estimating the impact of soil moisture on soil temperature. Therefore, based on the experiments conducted in Wuchuan County in 2020, this study proposes a soil water and heat coupling model that includes radiation, evaporation, soil water transport, soil heat conduction and ground temperature coupling modules to simulate the soil temperature and moisture and subsequently estimate the effects of soil moisture. The results show that the model performs well. The Nash–Sutcliffe coefficient (NSE) and the concordance index (C) of the simulated and measured values under each treatment are higher than 0.26 and 0.7, respectively. The RMSE of the simulation results is between 0.0067–0.017 kg kg⁻¹ (soil moisture) and 0.43–1.06 °C (soil temperature), respectively. The simulated values matched well with the actual values. The soil moisture had a noticeable regulatory effect on the soil temperature change, the soil surface temperature would increase by 0.08–0.43 °C for every 1% decrease in soil moisture, and with the increase in soil moisture, the variation of the soil temperature decreased. Due to the changes in the solar radiation, the sensitivity of the soil temperature to the decline in soil moisture was the greatest during June–July and the least in September. Moreover, the contributions of soil moisture changes to temperature increase under various initial conditions are inconsistent, the increase in sunshine hours, initial daily average temperature and decrease in leaf area index (LAI), soil density and soil heat capacity can increase the soil surface temperature. The results are expected to provide insights for exploring the impact mechanism of regional climate change and optimizing the structure of agricultural production.