## 3 Results
### Change Trend Characteristics of GPP, NPP and CUE  
Compared with the reference period of 1951-2014, the mean GPP deviations for the three climate scenarios showed an increasing trend in the future long time series (Figure 1a). From 2015 to 2010, under the scenarios of SSP1-2.6, SSP3-7.0 and SSP5-8.5, the multi-year mean GPP is 31.38-38.82, 30.99-54.52 and 31.57-62.53 gCm\({}^{-2}\)a\({}^{-1}\), respectively, and compared with the historical period, the annual average deviations of GPP are 3.03-10.48, 2.65-26.17 and 3.21-34.17 gCm\({}^{-2}\)a\({}^{-1}\), respectively. In future long-term series (2015-2100), GPP increases with increasing radiation forcing. Under the three scenarios on the interannual scale, the tendency rates of GPP are 0.0567, 0.2689 and 0.3670 gCm\({}^{-2}\)a\({}^{-1}\) (Table 1), which reach a substantial level. With the increase in radiation forcing, the increasing trend becomes increasingly larger.  
The deviation values of NPP in different scenarios relative to historical periods are consistent with GPP in future long time series (Figure 1b). In 2015-2100, under the scenarios of SSP1-2.6, SSP3-7.0 and SSP5-8.5, the annual mean NPP values are 16.82-20.72, 16.73-28.98 and 16.76-32.81 gCm\({}^{-2}\)a\({}^{-1}\), respectively. The annual average deviations of NPP are between 1.78-5.68, 1.69-13.94 and 1.73-17.77 gCm\({}^{-2}\)a\({}^{-1}\). At the interannual scale, the NPP propensity rates of the three scenarios are 0.0276, 0.1398 and 0.1886 gCm\({}^{-2}\)a\({}^{-1}\) (Table 1), reaching substantial levels, and the increasing trend is obvious with the increase in radiation forcing. Under the same scenario, the tendency rate of GPP is higher than that of NPP, which indicates that the growth rate of GPP is higher than that of NPP in each scenario. Comparing GPP and NPP under the same scenario, the NPP value is close to half of the GPP value, i.e., the CUE (NPP/GPP) value is approximately 0.5.  
From 2015 to 2100, the CUE values of the SSP1-2.6, SSP3-7.0 and SSP5-8.5 scenarios ranged from 0.502 to 0.520, 0.498 to 0.522 and 0.497 to 0.520, respectively (Figure 2). The results reveal that CUE shows different degrees of decline under the scenarios of SSP1-2.6, SSP3-7.0 and SSP5-8.5 in the future long-term series in the Qinghai-Tibet Plateau. The tendency rates of CUE in the SSP1-2.6, SSP3-7.0 and SSP5-8.5 scenarios are \(-3.50\times 10^{-5}\), \(-1.12\times 10^{-4}\) and \(-1.76\times 10^{-4}\), respectively (Table A1). This result indicates that with the increase in radiation forcing, the downward trend of CUE in the long-term series increases in turn, and the stronger the radiation is, the smaller the value of CUE. Under the same scenario, the tendency rate is higher than that of NPP, and with the increase in radiation forcing, the rate of increase in GPP is higher than that of NPP, which also explains the change in CUE from the other side.  
Figure 1: The regionally averaged annual GPP anomaly is shown in (a); the annual NPP anomaly is shown in (b) (units: gCm\({}^{-2}\)a\({}^{-1}\)). They are over the Qinghai-Tibet Plateau during 2015-2100 relative to 1951–2014 under the SSP1-2.6, SSP3-7.0 and SSP5-8.5 scenarios as derived from five models and their ensemble mean with the same weights (MME). The tendency rates of GPP and NPP are shown in the legend.  
Figure 2: Trend of CUE over the Qinghai-Tibet Plateau during 2015–2100 under the SSP1-2.6, SSP3-7.0 and SSP5-8.5 scenarios as derived from five models and their ensemble mean with the same weights. The tendency rate of CUE is shown in the legend.