## 3 Results
### Contributions of Changes in Important Influencing Factors to WUE Trend
#### 3.3.2 Contributions of Important Influencing Factors to WUE Trend  
According to Equations (9) and (10), the contributions of LAI and climatic-factor variations to the WUE trend were calculated according to the normalized ridge-regression  
Figure 7: Spatial distribution of variation trends of (**a**) LAI, (**b**) PRE, (**c**) RH, and (**d**) WS. coefficient and the linear trend of the variables (Figure 8). The contribution of LAI changes to the WUE trend was between \(-0.135\) and \(0.168\) g C m\({}^{-2}\) mm\({}^{-1}\) yr\({}^{-1}\) (Figure 8a). Areas with positive and negative contributions accounted for \(85.15\%\) and \(14.85\%\) of the whole study area, respectively. LAI mainly had a positive effect on the WUE trend. There was an increasing trend of LAI in \(85.03\%\) of the study area, and LAI had positive effects on the WUE trend (Table 2). The regions of high contributions were mainly in Erdos, Hohhot, south Ulanqab, central Xilingol League, Hinggan League and west Hulunbuir, with contribution values over \(0.008\) g C m\({}^{-2}\) mm\({}^{-1}\) yr\({}^{-1}\). There was a decreasing trend of LAI in only \(9.86\%\) of the study area, where LAI had a negative contribution to the WUE trend. These areas were mainly distributed in southwest Hulunbuir, north Chifeng and southwest Xilingol League. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Contribution** & **Influencing** & **Increasing** & **Decreasing** & **Sum (\%)** \\
**Type** & **Factors** & **Trend (\%)** & **Trend (\%)** & **Sum (\%)** \\ \hline \hline \multirow{3}{*}{Positive contribution} & LAI & 85.03 & 0.12 & 85.15 \\  & PRE & 62.78 & 0.06 & 62.84 \\  & RH & 12.62 & 46.98 & 59.60 \\  & WS & 22.68 & 13.57 & 36.25 \\ \hline \hline \multirow{3}{*}{Negative contribution} & LAI & 4.99 & 9.86 & 14.85 \\  & PRE & 36.95 & 0.21 & 37.16 \\  & RH & 15.86 & 24.54 & 40.40 \\ \cline{1-1}  & WS & 52.84 & 10.91 & 63.75 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Proportion of the contributions of LAI, PRE, RH, and WS variations to the WUE trend. Figure 8: Spatial distribution of the contributions to WUE trends contributed by the changes in (**a**) LAI, (**b**) PRE, (**c**) RH, and (**d**) WS. The contribution of annual precipitation to the WUE trend was \(-\)0.029-0.039 g C m\({}^{-2}\) mm\({}^{-1}\) yr\({}^{-1}\) (Figure 8b). There was an increasing trend of precipitation in 62.84% of the study area, where there was positive contribution to the WUE trend (Table 2). High-contribution areas were concentrated in central Hulunbuir, indicating that increasing precipitation might have had positive effects on the local WUE variation. Increasing precipitation had a negative contribution to the WUE in 36.95% of the study area, mainly in Baotou, Hohhot, northeast Xilingol League, south Hinggan League along Chifeng, as well as west and northeast Hulunbuir. The areas where there were positive and negative effects of relative humidity on WUE accounted for 59.60% and 40.40%, respectively (Table 2). Relative humidity decreased in Bayannur, south Ulanqab, west Xilingol League and north Hulunbuir, which had a positive contribution to the WUE trend (Figure 8c). Increasing relative humidity had a negative contribution to the WUE trend in Hinggan League and east Hulunbuir. The contribution of wind speed was within 0.054-0.069 g C m\({}^{-2}\) mm\({}^{-1}\) yr\({}^{-1}\) (Figure 8d). Wind speed increased in central Hulunbuir and Erdos, and its contribution to the WUE trend was positive, accounting for 22.68% of the study area (Table 2). Areas where there was a negative contribution of wind speed to the WUE trend accounted for about 63.75% of the study. Increasing wind speed had a negative contribution to the WUE in Xilingol League and Erdos. The maximum negative contribution was observed in Hulunbuir.