Terrestrial and Atmospheric Controls on Surface Energy Partitioning and Evaporative Fraction Regimes Over the Tibetan Plateau in the Growing Season

Abstract

Land-atmosphere interactions are an essential component of the climate system. However, no detailed description of the underlying effects of the surface forcing of the atmosphere has been established. In this study, GLEAM, MODIS, and ERA5 were the input set of multiple analysis algorithms, "segmentation" was the core idea of the analysis method. The study area is segmented into six surface response functional groups, and the multidimensional evaporation regime function was segmented into piecewise functions controlled by segment authoritative variables. Inspired by the surface heat balance equation and moisture-limited, energy-limited evaporation regimes, we chose soil moisture content and the net radiation flux to represent the moisture and energy status, respectively, and chose the leaf area index (LAI) to characterize the vegetation cover to investigate the primary effects of surface parameters on the energy partitioning of the land surface and evaporative regime. The results show that though a coupling strength 1.8 times greater was obtained when the LAI was used as the response variable instead of soil moisture, soil moisture was still the highest response variable in the regression tree analysis. This is consistent with the essence of the evaporative fraction and indicates that water should be the most fundamental response variable. The evaporative regime was subdivided from two phases into five phases according to the effects such as water extraction by vegetation, photosynthesis, soil shading, and roughness changes, each with an authoritative response variable.