## 4 Discussion
### Effects of Vegetation and Climate Change on ET in the HLS  
Following the simulation and validation of ET, we further investigated the effects of climate change on ET and its components within the HLS. When analyzing the influence of climate factors on ET, we observed that temperature (TMP) had a more pronounced impact, exhibiting a negative contribution in the central and southern regions, while contributing positively in the northern and western regions. High temperature intensifies transpiration and soil evaporation, but may also lead to soil drying, which limits further ET [43]. In the central and southern regions, persistent high temperatures can cause the rapid evaporation of soil moisture, preventing vegetation roots from absorbing water promptly, which leads to water deficits in plants and weakens transpiration, ultimately reducing the overall ET [8]. In the northern and western regions, a moderate increase in temperature may contribute to an increase in plant growth and ET, especially in the relatively low-temperature season. A moderate temperature increase can promote the photosynthesis and growth of plants and enhance transpiration. The contribution of radiation (RAD) to ET was mainly positive, with a higher contribution rate in the central region, while the southern and northern regions showed a negative contribution. The higher radiation in the central region promoted photosynthesis and transpiration, thus increasing ET [44]. Increased radiation usually increases leaf temperature and photosynthetic efficiency and increases the transpiration rate of water through the stomata. Therefore, in the central region with sufficient light, the increase in radiation significantly increased ET. The negative contribution of the southern \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Pathway** & **PRE** & **RAD** & **TMP** & **VFD** & **ET** & **Et** & **Ei** & **Es** \\ \hline LAI\(\rightarrow\) & 0.432 \({}^{\ast}\) & 0.173 & 0.198 & \(-\)0.008 & 0.006 & \(-\)0.003 & \(-\)0.065 & 0.108 \\ PRE\(\rightarrow\) & & & \(-\)0.22 & \(-\)0.654 \({}^{\ast}\) & 0.523 \({}^{\ast}\) & 0.553 \({}^{\ast}\) & 0.487 \({}^{\ast}\) & \(-\)0.162 \\ RAD\(\rightarrow\) & & & 0.016 & & 0.265 & 0.242 & 0.314 & 0.052 \\ TMP\(\rightarrow\) & & & & \(-\)0.213 & \(-\)0.228 & \(-\)0.319 & 0.19 \\ VPD\(\rightarrow\) & & & & & \(-\)0.366 & \(-\)0.363 & \(-\)0.327 & \(-\)0.024 \\ \hline \end{tabular} Note: \({}^{\ast}\)_p_ < 0.05. \(\rightarrow\): The path coefficient starting from the left factor, LAI\(\rightarrow\): The path coefficient starting from LAI.  
\end{table} 
Table 4: The path coefficient of LAI, PRE, TMP, RAD, and VPD on the changes in ET, Et, Ei, and Es based on the PLS-SEM model. and northern parts may be due to the reduction in vegetation damage and ET caused by excessive radiation. Excessive radiation may lead to photoinhibition in plants, reduce the efficiency of photosynthesis, and even cause leaf burns, damage plant health, and reduce ET [45]. The negative contribution of VPD to ET was significant in most regions, especially in the southern region. An increase in VPD usually enhances ET demand, but if soil moisture is insufficient, it may limit the actual occurrence of ET [46]. High VPD means high air dryness and enhanced transpiration in plants. However, if the soil moisture is insufficient, then the plant's roots cannot provide sufficient water, and transpiration will be limited. Therefore, in the southern region, although VPD is high, it leads to a decrease in ET due to insufficient soil water supply. The positive contribution of PRE to ET was mainly concentrated in the northern and central regions, while the southern region showed a negative contribution. This phenomenon may be related to the soil type and vegetation type in the region, which may limit the positive effect of PRE on ET.