## 3 Results
### Spatial Variation in NPP and the Responses from Different Ecosystem Types  
Under the RCP2.6 scenario, the NPP of about 39.38% of the urban ecosystem, mostly located in the western and southern Phoenix, would not change much (the grey areas in Figure 4a) during the 21 st century, while the strongest NPP increase (generally \(>\)60 g C/m\({}^{2}\)) would be found in the agricultural lands located in western and southeastern Phoenix. Under the RCP4.5 and RCP8.5 scenarios, most of the urban ecosystems, except for the industrial and transportation lands that mainly locate to the north of Salado River, would see a significant increase of NPP (\(>\)40 g C/m\({}^{2}\) under the RCP4.5 scenario, and \(>\)75 g C/m\({}^{2}\) under the RCP8.5 scenario) during the 21 st century, with the strongest NPP increase (\(>\)200 g C/m\({}^{2}\) under the RCP8.5 scenario) found in the mesic residential areas that mainly locate in the east, south, and southwest of the Phoenix Mountains Preserve (including Moon Hill, Shaw Butte, North Mountain, Stoney Mountain, Dreamy Draw, Squaw Peak, and the informally named Quartzite Ridge [44]) (Figure 4b,c). Among the different ecosystem types (or land-cover type), the crop ecosystems would have the strongest NPP increase (at least 43% stronger than any other ecosystem type), followed by the urban lawn and forests, while the remnant dryland including shrubland and grassland would have the weakest NPP increase, under the RCP4.5 and RCP8.5 scenarios (Figure 5). Under the RCP2.6 scenario, the situation will be more complicated. The NPPs of all ecosystem types were projected to increase during the 1 st half of the 21 st century. Then, as the CO\({}_{2}\) concentration declining in the 2 nd half of the century under the RCP2.6 scenario, the increase trend of NPP would disappear (in the natural dryland ecosystems) or even reverse (in the urban forest and lawn that would have accumulated large biomass during the first half of the century). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**RCP2.6**} & \multicolumn{3}{c}{**RCP4.5**} & \multicolumn{3}{c}{**RCP8.5**} \\ \cline{2-10}  & **2006–2050** & **2050–2099** & **2006–2099** & **2006–2050** & **2050–2099** & **2006–2099** & **2006–2050** & **2050–2099** & **2006–2099** \\ \hline OVERALL & 53.78 & \(-\)5.26 & 48.51 & 80.69 & 87.49 & 168.18 & 130.66 & 183.78 & 314.44 \\ CO\({}_{2}\) & 42.78 & \(-\)15.76 & 27.03 & 65.86 & 35.97 & 101.82 & 88.24 & 91.16 & 179.4 \\ TMP & 23.14 & 0.65 & 23.78 & 1.07 & 17.46 & 18.53 & 22.92 & 11.34 & 34.26 \\ PPT & \(-\)12.19 & 12.46 & 0.27 & 12.8 & 20.44 & 33.23 & 11.78 & 17.79 & 29.57 \\ INTACTIVE & 0.04 & \(-\)2.61 & \(-\)2.57 & 0.97 & 13.62 & 14.59 & 7.72 & 63.49 & 71.21 \\ \hline \multicolumn{10}{c}{OVERALL: the multiple factors experiment that simulated combined effect of climate and CO\({}_{2}\) change on NPP; CO\({}_{2}\): the CO\({}_{2}\) experiment that CO\({}_{2}\) was transient during 2000–2099 while climate data were equilibrium level; TMP: the temperature experiment that temperature was transient while CO\({}_{2}\) and precipitation were equilibrium level; PPT: the precipitation experiment that precipitation was transient while CO\({}_{2}\) and temperature were equilibrium level; and INTACTIVE: the interactive effect between climate change and CO\({}_{2}\) change. RCP2.6: RCP is Representative Concentration Pathway, while 2.6, 4.5 and 8.5 are the radiative forcings of year 2100 in contrast to year 1750. NPP is net primary productivity. Unit: K ton C.} \\ \hline \end{tabular}
\end{table} 
Table 4: Results of factorial analysis in Phoenix. Figure 4: Spatiotemporal pattern of NPP (g C/m\({}^{2}\)) in the Phoenix city during 2006–2099 as simulated by HPM-UEM: **(a)** RCP2.6 scenario; **(b)** RCP4.5 scenario; and **(c)** RCP8.5 scenario.