## 3 Results
### Response of WUE to GPP and ET  
In order to explore the response of WUE changes to GPP and ET in the YRB from 1982 to 2018, this paper has categorized and discussed the effects of GPP and ET changes on WUE (Figure 9 and Table 3). The changes in WUE were divided into eight categories: WUE increase (GPP increase and ET increase; GPP increase and ET decrease; GPP decrease and ET increase; GPP decrease and ET decrease) and WUE decrease (GPP increase and ET increase; GPP increase and ET decrease; GPP decrease and ET increase; GPP decrease and ET decrease).  
From 1982 to 2018, 70.39% of the WUE showed an increasing trend (Slope > 0), which was mainly attributable to GPP increase and ET increase, and the rate increase in GPP was higher than the rate increase in ET. The distribution is primarily in Inner Mongolia, southern Shaanxi, Ningxia, Gansu, and Qinghai. A total of 29.61% of WUE showed a decreasing trend (Slope < 0), mainly attributed to GPP increase and ET increase. However, the ET's increase rate was higher than that in GPP (20.94%), and there was a mismatch between the increase rates of ET and GPP. From 1982 to 2000, there were 60.24% of WUE,  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**WUE** & **GPP and ET** & \multicolumn{2}{c}{**1982-2018**} & \multicolumn{2}{c}{**1982-2000**} & \multicolumn{2}{c}{**2000–2018**} \\ \cline{3-8}
**Change** & **Change** & **Area** & **Total** & **Area** & **Total** & **Area** & **Total** \\ \hline \multirow{3}{*}{WUE} & GPP \(\downarrow\) and ET \(\downarrow\) & 1.10 & & 7.35 & & 3.51 & \\  & GPP \(\downarrow\) and ET \(\uparrow\) & 7.55 & & 12.64 & & 12.81 & \\ decrease & GPP \(\uparrow\) and ET \(\downarrow\) & 0.02 & & 1.42 & & 0.30 & \\  & GPP \(\uparrow\) and ET \(\uparrow\) & 20.94 & & 18.35 & & 17.45 & \\ \hline \multirow{3}{*}{WUE} & GPP \(\downarrow\) and ET \(\downarrow\) & 0.03 & & 0.67 & & 0.37 & \\  & GPP \(\downarrow\) and ET \(\uparrow\) & 0.04 & & 0.35 & & 0.73 & \\ increase & GPP \(\uparrow\) and ET \(\downarrow\) & 0.30 & & 5.55 & & 1.36 & \\  & GPP \(\uparrow\) and ET \(\uparrow\) & 70.02 & & 53.67 & & 63.47 & \\ \hline \hline \end{tabular} Note: “\(\uparrow\)” denotes an increase in the trend, “\(\downarrow\)” denotes a decrease in the trend.  
\end{table}
Table 3: The percentage of area in response to changes in WUE to GPP and ET at different time periods.  
Figure 9: WUE changes in response to GPP and ET across different time periods.  
which showed an increasing trend (Slope > 0), mainly attributed to GPP increase and ET increase (53.67%) and GPP increase and ET decrease (5.55%). However, 39.76% of the WUE exhibited a decrease trend, mainly because of the GPP decrease and ET increase (12.64%) and the GPP decrease and ET decrease (18.35%).  
Figure 10 and Table 4 indicated the significant changes in GPP and ET on WUE after passing the test of significance (significance test \(p\) < 0.05). From 2000 to 2018, 65.39% of WUE showed an increasing trend (Slope > 0), mainly because of the GPP increase and ET increase, and the increase rate of GPP was greater than the increase rate of ET (63.47%). A total of 18.89% of WUE showed an increasing trend (Slope > 0, \(p\) < 0.05), and the significant increase in GPP and ET significantly contributed to the enhancement of WUE within the YRB. The part of the significant increase in WUE is mainly located in Gansu, Ningxia, and northern Shaanxi.