## 3 Results
### Contributions of Meteorological Factors to Vegetation WUE Variations  
The relative contributions of precipitation, shortwave radiation, temperature, and VPD to WUE variation were calculated based on ridge regression analysis (Figures 27 and 7a). For the whole of China, VPD had the highest relative contribution to interannual WUE variations across the entire region (38.64%). Its influence was most pronounced in SC (66.03%), where the relative contribution was 1.94 times higher than in other regions (34.08%), making VPD the primary driver of WUE interannual changes (Figures 27d and 7a). Temperature ranked as the second most influential factor, with an average relative contribution of 23.99% (Figure 7a). Areas with higher temperature contributions were mainly located in the eastern part of SW, as well as CC and EC (Figure 27c). Precipitation showed the highest relative contribution in SW (26.85%), with high-value areas concentrated in the western part of the region and parts of NE, while SC exhibited the lowest contribution from precipitation (8.09%). These findings suggest that precipitation plays a more significant role in influencing WUE interannual changes in arid and semi-arid regions (Figures 27a and 7a). Shortwave radiation contributed minimally to WUE variations across all regions, indicating its relatively limited role compared to the other factors.  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & **WSN** & **SN** & **GL** & **ENF** & **EBF** & **DBF** & **MXF** & **CL** \\ \hline WUE\({}_{\text{max}}\) & 36.06 & 6.56 & 23.77 & 2.46 & 4.92 & 1.64 & 4.92 & 19.67 \\ WUE\({}_{\text{min}}\) & 33.93 & 4.47 & 27.68 & 3.57 & 4.47 & 4.46 & 4.46 & 16.96 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The proportion of vegetation types with changes in the dominant factors of extreme WUE from 2001–2010 to 2011–2020 (unit: %).  
Figure 6: The spatial distribution of the relative contributions of (**a**) Prec, (**b**) Srad, (**c**) Temp, and (**d**) VPD to interannual variations in WUE.  
The absolute contributions of meteorological variable changes to WUE can be classified into positive and negative contributions. Positive contributions indicate a positive impact on WUE, while negative contributions signify an adverse effect. Across the entire region, changes in VPD primarily contributed positively to WUE (Table 3). In SC, 95.51% of the area experienced positive VPD contributions, whereas only 4.99% of the area showed negative contributions (Figure 8d and Table 3). Notably, the positive contribution of VPD in SC was 1.57 times greater than the average across the other six regions (Figure 7b). Outside SC, high positive VPD contributions were observed in NE, particularly in farmlands, grasslands, and woody savannas (Figure 8d). Precipitation and shortwave radiation exhibited negative contributions to WUE in 55.77% and 61.54% of SC, respectively, and the areas with positive contributions exceeded those with negative contributions, indicating an overall positive impact on WUE in other regions (Table 3). Temperature, in contrast, had a consistently positive effect on WUE across the entire study area. In CC, 80.10% of the area exhibited positive temperature contributions, with the magnitude being 3.09 times higher than the average positive temperature contribution across the other six regions (Figure 8c and Table 3).  
Figure 8: The spatial distribution of the absolute contributions of (**a**) Prec, (**b**) Srad, (**c**) Temp, and (**d**) VPD to interannual variations in WUE.  
Figure 7: (**a**) Relative contributions rate and (**b**) absolute contributions of changes in Prec, Srad, Temp, and VPD to WUE for sub-regions.