Quantitative Analysis of the Influence of Shallow Soil Temperature and Moisture on Surface Energy and Water Exchange on the Tibetan Plateau

The complex topography and land surface conditions of the Tibetan Plateau (TP) result in uncertainty and nonlinearity of energy and water exchange between land and atmosphere. The quantification of nonlinear interactions facilitates understanding of complex land-atmosphere interaction on TP. The Conditional Mutual Information (CMI) difference method and ERA5-Land reanalysis dataset are involved to analyze the influence of shallow soil temperature and moisture on surface sensible and latent heat fluxes on TP. The results indicate as below. (1) There is a significant spatial difference about the sensitivity of sensible and latent heat fluxes on the shallow soil temperature and moisture on TP. The shallow soil is drier in central TP and Qaidam basin where the difference of CMI (∆I) is greater than 0.6. The sensible and latent heat fluxes exhibit greater sensitivity to soil moisture than soil temperature. Conversely, the shallow soil is wetter in eastern TP and western TP where ∆I is below -0.6. The sensible and latent heat fluxes exhibit greater sensitivity to temperature than soil moisture. (2) The strength of these sensitivities appears obvious seasonal variations. In soil moisture-sensitive regions, latent heat flux reaches maximum in summer while sensible heat flux in autumn. In soil temperature-sensitive regions, both latent and sensible heat fluxes reach maximum in summer. (3) The spatial distribution and seasonal variations of sensitivity of surface evaporation to shallow soil temperature and moisture on TP are consistent with latent heat flux, while those of land-air temperature difference are consistent with sensible heat flux. The correlation coefficient between ∆I of surface evaporation and latent heat flux is 0.48, while that between the land-air temperature difference and sensible heat flux is 0.65. They all pass the significance test at the 99% level. In summary, shallow soil temperature and moisture dominate surface evaporation and land-air temperature difference on TP and future influence the spatiotemporal characteristics of surface sensible and latent heat fluxes.