## 3 Results
### The Dominance of Water Stress to Vegetation Growth in Global Drylands
#### 3.4.1 Offset in the Contribution Among CO\({}_{2}\), SW, and VPD Based on Satellite Observations
This indicates that increased VPD and SW constraints resulted in greater negative stress on the forestland ecosystem, followed by croplands and grasslands (Figure 9c). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Area Percentage (\%)**} & \multicolumn{3}{c}{**The Offsetting Types**} \\ \cline{2-4}  & **VPD vs. CO2** & **SW vs. CO2** & **VPD and SW vs. CO2** \\ \hline The offsetting proportion & 25.36 & 37.33 & 38.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Area proportion of the VPD- and SW-induced negative contributions to vegetation growth offsetting the CO2-induced positive contribution. Figure 8: Comparisons of contributions in the VPD- and SW-induced LAI decreases with CO2-induced LAI increases across global drylands from 1982 to 2018. (**a**) Rising VPD-induced negative contributions counteracting the CO2-induced positive contributions, (**b**) decreasing SW-induced negative contributions counteracting the CO2-induced positive contributions, and (**c**) VPD- and SW-induced negative contributions counteracting the CO2-induced positive contributions. Meanwhile, the study further explored the differences in the area proportion of decreasing SW-induced LAI decreases at different soil depths offsetting the rising CO\({}_{2}\)-induced increases in LAI, as shown in Figure 10. The regions with the highest offsetting degree (>30% offsetting proportion) across various soil depths accounted for approximately 8.48% (SW1, Figure 10a), 9.88% (SW2, Figure 10b), 9.91% (SW3, Figure 10c), and 8.10% (SW4, Figure 10d) of CO\({}_{2}\)-fertilized areas of global drylands. The spatial patterns of the offsetting proportion among different soil depth-stressed ecosystems consistently indicated that decreasing SW-induced LAI decreases at different soil depths greatly offset rising CO\({}_{2}\)-induced increases in LAI, especially in central Asia and southeastern Australia. In conclusion, SW-stressed ecosystems were greatly constrained by increasing SW constraints at the second (7-28 cm) and third (28-100 cm) soil depths across global drylands during the period of 1982-2018. Figure 10: The differences in the contribution of SW-induced LAI decrease offsetting the CO\({}_{2}\)-induced LAI increases at different soil depths across global drylands from 1982 to 2018: (**a**) 0–7 cm, (**b**) 7–28 cm, (**c**) 28–100 cm, and (**d**) 100–289 cm. Figure 9: Statistical distribution of the proportion of the offsetting contributions in different landcovers in global drylands from 1982 to 2018. (**a**) VPD-induced decreases in LAI offsetting the positive contributions of CO\({}_{2}\) fertilization, defining VPD vs. CO\({}_{2}\); (**b**) SW-induced decreases in LAI offsetting the positive contributions of CO\({}_{2}\) fertilization, defining VPD vs. SW; and (**c**) VPD- and SW-induced decreases in LAI offsetting the positive contributions of CO\({}_{2}\) fertilization, defining VPD+SW vs. CO\({}_{2}\). 4.2 Comparison of the Contributions of Driving Factors Between Process-Based Models and Satellite Observations  
Further, this study quantified the contributions of influencing factors to LAI changes in global drylands from 1982 to 2018 using 11 state-of-the-art ecosystem models and satellite observations, as shown in Figure 11. Multi-model averaging (MMA) of 11 ecosystem models from the TRENDY project showed that CO2 concentration and climate change positively contributed to greening dryland ecosystems, in which CO2-induced increases in LAI reached up to 3.10 \(\times\) 10\({}^{-3}\) m\({}^{2}\cdot\)m\({}^{-2}\), and climate change-induced increases in LAI were 0.30 \(\times\) 10\({}^{-3}\) m\({}^{2}\cdot\)m\({}^{-2}\). While land cover changes exhibited negative contributions to the trend of LAI, LCC-induced decreases in the LAI trend reached up to \(-\)0.40 \(\times\) 10\({}^{-3}\) m\({}^{2}\cdot\)m\({}^{-2}\), as shown in Figure 11a.