## 3 Results
### NEP Simulations under All Sky Conditions during 2013-2016
#### 3.3.4. NEP Simulations Using EMGPP and Re (LDR) Models  
Thirdly, the hourly NEPs were calculated using EMGPP and Re (LDDR) (with the 3-factor and 2-factor methods) and Tables 17 and 18, and Figures 12 and 13 gives the results. Similar ratios were found for the mean daily, monthly, and annual sums. The estimated  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Time**} & \multirow{2}{*}{**\(\delta\)avg**} & \multirow{2}{*}{**NMSE**} & \multirow{2}{*}{\(\sigma_{\text{cal}}\)} & \multirow{2}{*}{\(\sigma_{\text{obs}}\)} & \multirow{2}{*}{**cal/obs**} & \multirow{2}{*}{\(n\)} & \multicolumn{2}{c}{**MAD**} & \multicolumn{2}{c}{**RMSE**} \\ \cline{5-10} \cline{6-10} \multicolumn{1}{c}{**Period**} & & & & & & & & **(mgCO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\))** & \multicolumn{1}{c}{**(\%)**} & \multicolumn{1}{c}{**(mgCO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\))**} & \multicolumn{1}{c}{**(\%)**} \\ \hline
2013 & 112.71 & 0.496 & 0.369 & 0.291 & 1.17 & 2493 & 0.281 & 58.31 & 0.530 & 110.00 \\ \hline
2014 & 140.95 & 0.557 & 0.376 & 0.295 & 1.34 & 4181 & 0.289 & 69.00 & 0.536 & 127.94 \\ \hline
2013–2016 & 135.55 & 0.538 & 0.366 & 0.300 & 1.29 & 14,748 & 0.303 & 66.62 & 0.378 & 83.23 \\ \hline \hline \end{tabular}
\end{table}
Table 16: Same as Table 15, and for mean hourly GPP (mgCO\({}_{2}\) m\({}^{-2}\)) simulations (S/Q = 0–1) using 2-factor EMGPP.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Time**} & \multirow{2}{*}{**\(\delta\)avg**} & \multirow{2}{*}{**NMSE**} & \multirow{2}{*}{\(\sigma_{\text{cal}}\)} & \multirow{2}{*}{\(\sigma_{\text{obs}}\)} & \multirow{2}{*}{**cal/obs**} & \multirow{2}{*}{\(n\)} & \multicolumn{2}{c}{**MAD**} & \multicolumn{2}{c}{**RMSE**} \\ \cline{5-10} \cline{6-10} \multicolumn{1}{c}{**Period**} & & & & & & & **(mgCO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\))** & \multicolumn{1}{c}{**(\%)**} & \multicolumn{1}{c}{**(mgCO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\))**} & \multicolumn{1}{c}{**(\%)**} \\ \hline
2013 & 117.15 & 0.490 & 0.374 & 0.291 & 1.15 & 2493 & 0.287 & 59.43 & 0.535 & 111.05 \\ \hline
2014 & 148.47 & 0.612 & 0.392 & 0.295 & 1.37 & 4181 & 0.301 & 71.90 & 0.549 & 130.99 \\ \hline
2013–2016 & 14  
It was found that the Re and GPP simulations captured the monthly variations well, but the NEP simulations did not show a better performance than Re and GPP, and further studies are needed. The estimates of the annual sums of NEP were in reasonable agreement with the observed NEPs, and most of them were within 2 \(\sigma_{\text{obs}}\), except 2016.  
Given there were problems in CO\({}_{2}\) flux measurements in 2016 summer, the observational data in 2013-2015 were used for further comparisons; the ratios of the mean annual sum of the calculated to observed values were 1.07 and 1.12 for NEP using the 3-factor and 2-factor methods, respectively, 1.41 and 1.36 for Re, and 1.07 and 1.12 for GPP. So, EMNEP models displayed improved performances for NEP. The NEP simulations exhibited the largest uncertainty than GPP and Re; this feature was also found in other studies, e.g., the Yale Interactive terrestrial Biosphere (YIBs model) [65], because NEP has the positive and negative values and the smallest values compared to GPP and Re, and the most important reason is that NEP is associated with many complex processes and current limited understanding.  
According to the high NEP in the summer of 2013-2015, the measured low NEP in 2016 summer should be corrected, and the simulated NEP values can be used as a reference.