## 3 Results
### Trends in Climatic Factors and Their Mechanisms of Influence on ET  
The change in ET is driven by the change in water supply, atmospheric ET demand, and vegetation physiological characteristics. The initial part of this paper investigates the role of vegetation changes in ET over a 19-year period. Utilizing the multiple regression method, the study examines the effects of climate change on ET in the HLS from 2000 to 2018. Figure 11a shows the spatial distribution of the MK trend change in PRE in the HLS from 2000 to 2018. The results show that the PRE in the HLS shows an increasing trend, and the overall growth rate is greater than 3 mm/a. The growth rate in the central region is greater than that in the southern and northern regions. Figure 11b shows the spatial distribution of the MK trend change in TMP. TMP increased significantly in the northern and central regions of the HLS, while TMP decreased significantly in the southwestern region. Figure 11c shows that the RAD in the northern part of the HLS shows an increasing trend, and the increase rate is greater than 0.3 W/m\({}^{2}\)/a. The RAD in the southeastern region exhibited a declining trend, with a decrease rate of approximately 0.1 W/m\({}^{2}\)/a. As shown in Figure 11d, the VPD in the northern part of the HLS decreased at a rate of 0.001-0.003 kPa/a. Conversely, the RAD in the southeastern region demonstrated an increasing trend, with a rate exceeding 0.001 kPa/a. Figure 11e-h illustrate the distribution of significant changes in PRE, TMP, RAD, and VPD. PRE showed a marked increasing trend across most areas of the entire HLS. Significant increases in TMP and RAD were primarily concentrated in the central and northern regions. VPD exhibited a significant decreasing trend across most areas of the HLS. Figure 11i-l depict the trend in changes in PRE, TMP, RAD, and VPD in the HLS from 2000 to 2018. During this period, the annual PRE value increased from 400 mm to approximately 500 mm, indicating a clear upward trend with an average annual increase of 3.57 mm. The annual TMP value increased from about 7.84 \({}^{\circ}\)C to about 8.42 \({}^{\circ}\)C, with an average annual increase of 0.015 \({}^{\circ}\)C. The annual RAD value increased from about 460 W/m\({}^{2}\) to about 475 W/m\({}^{2}\), which also showed a significant upward trend, with an increase rate of 0.20 W/(m\({}^{2}\)-a). The annual VPD value decreased from about 0.45 kPa to about 0.41 kPa, showing a downward trend, with an average annual decrease of 6.43 kPa. Figure 10: **(a,b,d,e,g,h,j,k)** The average annual ET (Et, Ei, Es) in the HLS from 2000 to 2018 under the two scenarios. **(c,f,i,l)** The difference between ET and its components in the two situations in the HLS from 2000 to 2018. Figure 12 illustrates the spatial distribution of the impact of climatic factors on the variations of ET, Et, Ei, and Es in the HLS from 2000 to 2018. Figure 12a-d depict the influence of PRE, TMP, RAD, and VPD on ET changes. The contribution of PRE (Figure 12a) to ET change is generally positive across most regions, with a contribution rate of 0-0.5 mm/a in the northern and central areas, while it is negative in the southern region (\(-\)0.5-0 mm/a). The contribution of TMP (Figure 12b) to ET is more significant, and the central and southern regions show mainly negative contributions (\(-\)3-1 mm/  
positive contribution to ET, and the contribution rate in the central region was about 0.5-3 mm/a, while the southern and northern regions showed a negative contribution (\(-\)0.5-3 mm/a). The VPD (Figure 12d) in the HLS showed a strong negative contribution to ET, and the negative contribution rate in most areas exceeded 3 mm/a. Figure 12e-h show the contribution of different climatic factors to Et changes. The contribution of PRE (Figure 12e) to Et is mainly positive, concentrated in the northern and central regions, and the PRE in the southern region shows a negative contribution to Et.