###### Abstract
[PERSON] et al. [11] reported a significant increase in pan evaporation in the Chinese climate transition zone over the past 50 years, where this is opposite to the \"evaporation paradox\" commonly observed in other regions of the world and constitutes the unique \"anti-evaporation paradox\". The thickness of the stable boundary layer, height of the residual layer, and thickness of the convective boundary layer all exhibit stepwise reductions from the non-monsoon regions to the transition zone and continue to decrease stepwise to the monsoon regions [12]. [PERSON] et al. [13] showed that a reversal occurs in the relationship between ET and other environmental factors when the SM, wind speed, Rn, and Normalized Difference Vegetation Index (NDVI) reach certain thresholds. As a key factor in land-atmosphere coupling, ET is often described using complex mathematical relationships to capture the influence of the environment and the climate [14] and involves a certain degree of uncertainty [15]. Research has shown that the evaporative fraction (EF, defined as the latent heat flux normalized by latent plus sensible heat flux) can more clearly depict the constraining relationship between the process of ET and other elements in different climate zones than ET itself. When values of the daily Rn exceed their average level in the climate transition zone in the southern Great Plains of North America, the EF exhibits a linear correlation with the SM, and the relationship of coupling between them shows significant interannual differences [16]. The slope of this relationship is more strongly correlated with the status of growth of the underlying surface vegetation under the influence of other meteorological conditions, which is often a non-linear relationship [17]. [PERSON] et al. [18] used sensitivity experiments on the parameters of the land surface to quantitatively estimate land-atmosphere interactions by using the relationship between the EF and the SM. The results showed that changes in the SM in the climate transition zone can lead to average variations of 1.1-1.3 K in the surface temperature (Ta) that can reach 6-7 K [19]. This parametric relationship provides theoretical support for modeling SM-EF interactions. [PERSON] and [PERSON] [20] identified a strong linear correlation between the SM and the surface energy that represents strong land-atmosphere coupling under ideal weather conditions (i.e., clear skies, low winds, and no recent precipitation). [PERSON] et al. [21] identified a third-order relationship of polynomial fit between the SM and the EF in the Qinghai-Tibet Plateau to confirm the strong EF-SM coupling in high-altitude regions. Studies have also shown that when the leaf area index (LAI) is used instead of the SM, the strength of EF-LAI coupling is three times that of EF-SM coupling. The gross primary production (GPP) is also strongly coupled with the EF when the underlying surface contains crops [9]. It is thus clear that the EF exhibits strong characteristics of coupling with the SM, LAI, and GPP in climate transition zones, where the coupling relationship and its strength vary owing to regional climatic and elemental environmental differences. However, research on the relationship between the SM and EF in China's climate transition zone remains inadequate, such that the relationships between the LAI and EF and the GPP and EF remain unclear. To fill this gap in research, the authors of this study used a dataset based on environmental observations from the Lanzhou University (SACOL) station, which is located in a region with a semi-arid climate, to investigate the relationships between the SM and EF, the LAI and EF, and the GPP and EF in the climate transition zone of China.