## 3 Results and Discussion  
### Temporal Trends of Terrestrial NPP in China and Linkage with ENSO  
The national total simulated NPP in China changed with fluctuations, from 2.8 Pg C yr\({}^{-1}\) to 3.6 Pg C yr\({}^{-1}\), over the period of 1961-2016 (Figure 3), with an average of 3.1 \(\pm\) 0.2 Pg C yr\({}^{-1}\). Total NPP increased at a rate of 0.0076 Pg C yr\({}^{-1}\) since 1961. Based on the mean of 251 published global terrestrial NPP estimates from 1862 to 2011 by Ito [7], the total NPP of China accounted for approximately 5.52% of the global total NPP (mean of 251 estimates: 56.2 Pg C yr\({}^{-1}\)).  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Simulations** & **Scenario** & **History** & **Climate Change** & **CO\({}_{2}\) Change** \\ \hline
1 & A2\_CO\({}_{2}\) & CRU & No & A2 \\
2 & B1\_CO\({}_{2}\) & CRU & No & B1 \\
3 & RCP45\_CO\({}_{2}\) & CRU & No & RCP45 \\
4 & RCP85\_CO\({}_{2}\) & CRU & No & RCP85 \\
5 & A2\_C & CRU & A2 & No \\
6 & B1\_C & CRU & B1 & No \\
7 & RCP45\_C & CRU & RCP45 & No \\
8 & RCP85\_C & CRU & RCP85 & No \\
9 & A2\_Cuple & CRU & A2 & A2 \\
10 & B1\_Cuple & CRU & B1 & B1 \\
11 & RCP45\_Cuple & CRU & RCP45 & RCP45 \\
12 & RCP85\_Cuple & CRU & RCP85 & RCP85 \\ \hline \end{tabular}
\end{table}
Table 2: Configurations of historical and future climate and CO\({}_{2}\) in different simulations.  
The annual total NPP demonstrated distinct trends in different stages during 1961-2016. The average NPP over the periods of 1961-1980, 1981-2000, and 2001-2016 were 2.98 \(\pm\) 0.11 Pg C yr\({}^{-1}\), 3.11 \(\pm\) 0.14 Pg C yr\({}^{-1}\), and 3.27 \(\pm\) 0.18 Pg C yr\({}^{-1}\), respectively, and increased at rates of 0.0049 Pg C yr\({}^{-1}\), 0.0006 Pg C yr\({}^{-1}\), and 0.0306 Pg C yr\({}^{-1}\) in these periods. The increasing rate of national total NPP was higher in the period of 2001-2016 than those in the periods of 1961-1980 and 1981-2000. Meanwhile, larger interannual fluctuations were observed during 1981-2000. In the period of 1991-2000, the total NPP declined with fluctuations.  
The analyzing linkage of total NPP with ENSO was made to explain the interannual fluctuations of terrestrial NPP in China. The magnitude and pattern of precipitation in eastern China during summer and winter were greatly affected by the ENSO [59; 60; 61]. For example, during the development stage of the ENSO, deficient precipitation occurred over most of eastern China, with as much as 30%-50% decreases in precipitation in some areas. In contrast, abundant precipitation was observed in the Yangtze-Huai Plain. During the attenuation stage of the ENSO, precipitation mostly increases in the area of the middle-lower Yangtze plains and declines in the Yellow River basin and in northern, southern, and southwestern China [59]. Such ENSO-induced anomalies of precipitation would definitely affect NPP. [PERSON] [62] found that NPP in China declined remarkably in some EI Nino years.  
Since 1951, 14 global EI Nino events have been recorded, and the EI Nino events in 1982/1983, 1997/1998, and 2015/2016 were \"super level\". In addition, the EI Nino events in 1965/1966, 2004/2005, 2009/2010, and 2015/2016 were CP EI Nino, while others were EP EI Nino [29]. We used MEI provided by NOAA-CPC to define the ENSO events [63], and associated these events with NPP in China during 1961-2016. As shown in Figure 3, the terrestrial NPP of China declined remarkably in the EP EI Nino years and increased in the CP EI Nino years. Before 2000, all ENSO events were EP EI Nino except for the events in 1965/1966, and the total NPP simulated by the LPJ model had relatively low values in these ENSO years. After 2000, the ENSO events were mostly CP EI Nino, and the total NPP had relatively high values in these ENSO years. Additionally, the NPP often increased in the La Nina year. However, continuous La Nina events (1973-1975, 1998-2000) might induce NPP to decrease.