Does Soil Moisture Have an Influence on Near-Surface Temperature?

Abstract

The relationship between soil moisture (SM) and temperature at 2-m height (T2) is examined with long-term meteorological and soil observations and a single-column model. With the information flow (IF) and correlation analysis methods, results show that the distribution of SM depends on land use and land cover, while an increase in vegetation fraction corresponds to an increase in SM, and this dependence decreases with soil depth. There is causality between T2 and SM at all soil levels. Compared with those in deeper soil, higher IF values and correlations appear in the top soil levels, implying a stronger interaction between the top soil layer and the atmosphere. Meanwhile, most correlation coefficient values rank weak or moderate, and negative feedback is predominant with low IF values, indicating that the causality between them is relatively weak and also proving that SM is not the sole factor that influences changes of near-surface temperature. The single-column model demonstrates that an increase (decrease) in SM will result in cooler (warmer) T2 through the redistribution of surface heat flux, while changes in SM in the top soil layers have a stronger influence on T2 compared to those in deep soil layers. The duration of the atmospheric temperature inversion layer is also prolonged (reduced) with an increase (decrease) in SM. Impacts of SM on T2 vary with land use or vegetation fraction and also are more significant in warm months and the daytime than in cold months and nighttime. Moreover, large-scale and local circulations have steady influences on T2 in different weather conditions.