## 3 Results
### Identification of Factor Attributions for Variations in ET and GPP
#### 3.4.2 Actual Contributions of Influencing Factors  
Although Figures 7 and 8 show the relative contributions of influencing factors, they do not indicate positive or negative effects. The actual contributions calculated by Equation (27) can fill this gap. Figure 9 shows the significant spatial heterogeneity in the actual contributions of influencing factors. Precipitation has a very positive effect on ET trends in the east of TP and most of TCon, with values larger than 0.6 mm yr\({}^{-1}\). Precipitation makes a negative contribution in the middle of TP and has a slightly negative influence on most of the SubT sub-regions. As shown in Table 4, precipitation has a mean positive value of 0.93 mm yr\({}^{-1}\) for TCon and 0.02 mm yr\({}^{-1}\) for TP due the offset of negative effects in the middle of TP, which indicates the higher sensitivity of ET to rainfall in TCon. The lowest-ranking negative contribution in the west of TCon and south of TMon can be attributed to the large fraction of irrigation croplands. The actual positive contribution of temperature (>0.6 mm yr\({}^{-1}\)) mainly exists in the east of China and east of TP, while the west of China and most of TCon show negative effects on ET trends. In addition to TCon, the wind speed makes negative contributions in TMon, SubT, and TP, with values of \(-0.06\) mm yr\({}^{-1}\), \(-0.14\) mm yr\({}^{-1}\), and \(-0.14\) mm yr\({}^{-1}\), respectively. Although SH shows a significantly positive contribution to ET in the north of TMon and southeast of SubT, TMon (\(-0.04\) mm yr\({}^{-1}\)), TP (\(-0.12\) mm yr\({}^{-1}\)), and SubT (\(-0.39\) mm yr\({}^{-1}\)) show negative contributions based on the mean actual contributions (Table 4). Figure 8: PDFs of the relative contributions of influencing factors to GPP variations for four sub-regions. Prec is precipitation, Temp is temperature, WS is wind speed, SH is specific humidity, SR is solar radiation, LAIH is LAI influenced by human activities. The contribution of SR to ET variation is significantly positive at the Yunnan-Guizhou Plateau (Southwestern China) and has a negative effect across most of the country, which is consistent with the SH trend shown in Figure 9. Human activities make remarkably positive contributions in most of China. The value of the positive contribution is larger than 3.0 mm yr\({}^{-1}\) in the south of TMon as a result of performing the Grain to Green Program, in the southwest of SubT due to Rocky Desertification Integrated Management, and in the west of TCon due to the Returning Grazing-Growing Project. Human activities have weak effects on ET in TP, which is sparsely populated. Figure 10 shows that the spatial distributions of the actual contributions of the influencing factors to GPP are similar to those of ET. Table 4 shows that the actual contribution ranks to GPP are different for temperature in comparison with ET. The rankings of the positive contributions of temperature to GPP are SubT (0.48 g C m\({}^{-2}\) yr\({}^{-1}\)) > TMon (0.47 g C m\({}^{-2}\) yr\({}^{-1}\)) > TP (0.46 g C m\({}^{-2}\) yr\({}^{-1}\)) > TCon (0.04 g C m\({}^{-2}\) yr\({}^{-1}\)); the rankings \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sub-Region** & & **Prec** & **Temp** & **WS** & **SH** & **SR** & **LAIH** \\ \hline TMon & ET & 0.38 & 0.33 & \(-\)0.06 & \(-\)0.04 & \(-\)0.62 & 1.12 \\ GPP & 0.76 & 0.47 & 0.53 & 0.57 & \(-\)2.03 & 7.95 \\ ET & 0.93 & 0.00 & 0.17 & 0.12 & 0.04 & 0.87 \\ GPP & 1.14 & 0.04 & 0.53 & 0.27 & \(-\)0.17 & 3.35 \\ ET & 0.03 & 0.29 & \(-\)0.14 & \(-\)0.39 & \(-\)0.17 & 0.88 \\ GPP & 0.30 & 0.48 & 0.20 & 0.70 & \(-\)0.01 & 6.84 \\ ET & 0.02 & 0.18 & \(-\)0.14 & \(-\)0.12 & 0.03 & 0.39 \\ GPP & 0.18 & 0.46 & 0.09 & 0.00 & \(-\)0.02 & 0.95 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mean regional contributions of influencing factors to ET (mm yr\({}^{-1}\)) and GPP (g C m\({}^{-2}\) yr\({}^{-1}\)). Figure 9: Spatial patterns of actual contributions of influencing factors to ET variations.