ABSTRACT
Soil moisture (SM) and atmospheric humidity (AH) are crucial climatic variables that significantly affect the climate system. However, the combined influencing mechanisms of SM and AH on the land surface temperature (LST) under global warming are still unclear. Here, we systematically analyzed the interrelationships among annual mean values of SM, AH, and LST using ERA5-Land reanalysis data and revealed the role of SM and AH on the spatiotemporal variations of LST through mechanism analysis and regression methods. The results showed that net radiation, SM, and AH could well model the long-term variability of LST well and explain 92% of the variability. Moreover, SM played an essential and different role under the different LST backgrounds. The AH always displayed a greenhouse effect on the LST. This study provides essential insights into the global climate change mechanism from the surface hydrothermal processes perspective.
ABSTRACT
The water and energy in the land surface and lower atmosphere have a strong coupling relationship. Apart from the land surface temperature (Ts) and air temperature (Ta), the land surface-air temperature difference (Ts-Ta) is also an essential parameter reflecting the coupling process. However, the global spatiotemporal variations and influencing factors of Ts-Ta remain not well explored. Here, ERA5-land reanalysis data, GIMMS NDVI data, and elevation data were used to analyze the global spatiotemporal heterogeneity and influencing factors of Ts-Ta. It was found that annual mean Ts-Ta exhibited a decreasing trend from the equator to polar areas. And the annual Ts-Ta increased at 0.009 °C/10a from 1981 to 2020. The variations of global net radiation mainly determined the spatiotemporal heterogeneity of global Ts-Ta. The different properties of the land surface and near-surface atmosphere were the main factors affecting the Ts-Ta, including soil moisture, vegetation, snow cover, and the water vapor content in the atmosphere. In addition, Ts and Ta also affected each other. These findings are conducive to a better understanding of the land-atmosphere coupling, and it is of great significance to take better measures to adapt the global climate change.
Subject(s)
Climate Change , Soil , Seasons , TemperatureABSTRACT
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.
