## 3 Results  
### Temporal Change Pattern of NPP  
During the 21 st century (comparing the early-21 st century (2006-2010) with the late-21 st century (2005-2099)), the regional averaged air temperature in Phoenix city would increase by 0.80 \({}^{\circ}\)C, 0.69 \({}^{\circ}\)C, and 4.45 \({}^{\circ}\)C under RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively; the precipitation would increase 114.3% under RCP8.5 scenario but decrease by 1.9% and 0.2% under RCP2.6 and RCP4.5 scenarios, respectively. The atmospheric CO\({}_{2}\) concentration increased by 40.5 ppm, 156.99 ppm, and 545.85 ppm under RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively, as shown in Figure 2. The simulation indicated the climate changes and elevated CO\({}_{2}\) concentration would result in a net increase of urban ecosystem NPP in the Phoenix city (from 2006-2009), as shown in Table 3 and Figure 3a. The increase rates of NPP would differ strongly under the different future climate scenarios, ranging from 15% under the RCP2.6 scenario to 100% under the RCP8.5 scenario. During the 21 st century, the NPP would increase steadily under both the RCP4.5 and RCP8.5 scenarios, although the NPP increase rate of the later would be twice higher than the former. Under the RCP8.5 scenario, the NPP would increase 41% in both the 1 st half and the 2 nd half of the 21 st century. Under the RCP4.5 scenario, the increase rate of NPP would slow down slightly from 25% during the 1 st half of the century to 21% during the second half of the century, possibly related to the declined precipitation. In contrast, the NPP would first increase 16%, reaching peak by the mid of the 2040s, after which the growing trend would disappear under RCP2.6, possible related to the declined precipitation and the atmospheric CO\({}_{2}\) concentration. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Mean Annual NPP (K Ton C/Year)**} \\ \cline{3-5}  & & **RCP2.6** & **RCP4.5** & **RCP8.5** \\ \hline \multirow{3}{*}{Timeperiod} & Early-21 st century (2006–2010) & 327 & 327 & 315 \\  & Mid-21 st century (20048–2052) & 381 & 408 & 446 \\  & Late-21 st century (2005–2099) & 376 & 495 & 629 \\ \hline \multirow{2}{*}{NPP changes in the 1 st half of the 21 st century} & Magnitude of the change & 54 & 81 & 131 \\  & Change rate (\%) & 16\% & 25\% & 41\% \\ \hline \multirow{2}{*}{NPP changes in the 2 nd half of the 21 st century} & Magnitude of the change & \(-5\) & 87 & 184 \\  & Change rate (\%) & \(-1\%\) & 21\% & 41\% \\ \hline \multirow{2}{*}{NPP changes in the 21 st century} & Magnitude of the change & 49 & 168 & 314 \\  & Change rate (\%) & 15\% & 51\% & 100\% \\ \hline \end{tabular} Note: RCP is Representative Concentration Pathway, and 2.6, 4.5 and 8.5 are radiative forcing of year 2100 in contrast to year 1750. Mean annual NPP of the early-, mid- and late-21 st century are the mean NPPs of 2006–2010, 2048–2052 and 2095–2099, respectively. The NPP changes in the 1 st half of the 21 st century was calculated as the difference between the mean NPP in the mid-21 st century and that in the early-21 st century. The NPP changes in the 2 nd half of the 21 st century was calculated as the difference between the mean NPP in the late-21 st century and that in the mid-21 st century. The NPP changes in the 21 st century was calculated as the difference between the mean NPP in the late-21 st century and that in the early-21 st century. Unit: K ton C (1 K = 1000).  
\end{table} 
Table 3: Model projected changes in the total ecosystem NPP of the Phoenix city, AZ, during the 21 st century. Figure 2: Annual variations of environmental factors in three representative concentration pathway (including RCP2.6, RCP4.5, and RCP8.5) during the 21 st century. (**a–d**) is precipitation, tavg, tmax, and tmin in RCP2.6 scenario, respectively. (**e–h**) is precipitation, tavg, tmax, and tmin in RCP4.5 scenario, respectively. (**i–l**) is precipitation, tavg, tmax, and tmin in RCP8.5 scenario, respectively.