Influence patterns of soil moisture change on surface-air temperature difference under different climatic background.

The surface-air temperature difference (Ts-Ta) is the main contributor to the sensible heat flux, and also an important indicator for land degradation. However, as the main influencing factor, the effect of soil moisture (SM) on Ts-Ta at the global scale has not been well articulated. Here, based on the ERA5-land reanalysis data from 1981 to 2019, the impacts of SM on Ts-Ta were studied. It was found that Ts-Ta over 54% of the global land increased, and SM across 70.7% of the world land decreased. In the increased SM areas, the increased soil evaporation weakened the increasing trend of Ts resulting in smaller Ts-Ta. In the decreased SM areas, the latent heat flux increased with soil evaporation and Ts-Ta decreased when SM was relatively high, and the larger sensible heat flux due to decreased soil evaporation aggravated Ts-Ta when SM was relatively low. The effect of SM on Ts-Ta presented nonlinear relationship due to the different background value of SM and temperature. The variation of SM at low SM or low temperature areas had an amplification effect on Ts-Ta. These findings will provide new insights into the different regional characteristics of global changing climate and the improvement of land degradation assessment indicators.