## 4 Results and Discussion
### NPP Spatiotemporal Variation  
NPP mean value of Guangzhou changed from 331.5 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\) in 2001 to 366.3 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\) in 2003, and then to 273.2 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\) in 2006, and standard deviation is 10.2, 18.3 and 22.6 g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\), respectively. It increased by mean value of 34.8 g\(\cdot\)C\(\cdot\)m\({}^{-2}\) during the first three years and dropped fast \begin{table}
\begin{tabular}{c c c} \hline
**Code** & **LULC Types** & **NPP Mean Value** **(g\(\cdot\)C\(\cdot\)m\({}^{-2}\)\(\cdot\)yr\({}^{-1}\))** \\ \hline
1 & ENF & 388 \\
2 & EBF & 446 \\
3 & MF & 456 \\
4 & SL & 415 \\
5 & WS & 398 \\
6 & GL & 317 \\
7 & CL & 367 \\
9 & CL\&NVM & 373 \\ \hline \end{tabular}
\end{table} 
Table 2: Net primary productivity (NPP) mean values of the land use/land cover types in Guangzhou. \begin{table}
\begin{tabular}{c c c c c c} \hline  & \multicolumn{2}{c}{**2001–2003**} & \multicolumn{2}{c}{**2003–2006**} \\ \cline{2-5}  & **LULC Types** & **Variation of Total NPP** & \(\Delta\)**Area** & **Variation of Total NPP** & \(\Delta\)**Area** \\  & & **(\(\times\)10\({}^{6}\) g\(\cdot\)C)** & **(km\({}^{2}\))** & **(\(\times\)10\({}^{6}\) g\(\cdot\)C)** & **(km\({}^{2}\))** \\ \hline
1 & ENF & –17.0 & –58 & –26.7 & –33 \\
2 & EBF & 33.4 & 29 & –22.1 & –14 \\
3 & MF & 10.4 & 8 & 1.3 & 19 \\
4 & SL & –11.9 & –35 & 19.6 & 121 \\
5 & WS & 5.3 & 30 & –3.2 & 6 \\
6 & GL & –6.6 & –19 & –79.5 & –173 \\
7 & CL & 48.4 & 55 & 2.7 & 25 \\
9 & CL \& NVM & 5.0 & –12 & 8.0 & 94 \\ \hline \end{tabular}
\end{table} 
Table 3: Changes in LULC and NPP in Guangzhou from 2001 to 2006.  
by 93.1 g-C-m-2 during the last three years. The NPP obvious changes during the fast urbanization period is consistent with the study of [PERSON] [29]. A related study reported on the alternating effects of La Nina and El Nino on climate change during 1950-2005 [46]. By investigating the impacts of ENSO in Guangzhou, the positive correlation between the Nino3.4 Sea Surface Temperature (SST) index and monthly weather variables of temperature and precipitation using a significant t test suggested that ENSO had a clear effect on the meteorology variables. For Guangzhou, 2001 was a weak La Nina year, 2003 was a strong El Nino year, and 2005 was a weak El Nino year [65]. Thus, the rapid urbanisation accompanied by a short-term alteration of ENSO events, which have a boundary point in 2003, corresponds with an increasing NPP trend during the first period (2001-2003) and a decreasing trend during the latter period (2003-2006), as shown in Figure 4a. As illustrated in Figure 4, variations in NPP including the increasing and decreasing trends, were divided into three levels according to the dynamic index: slight change (\(|\)0%-5%\(|\)), moderate change (\(|\)5%-15%\(|\)) and obvious change (\(>\)\(|\)15%\(|\)), as shown in the statistical histogram (Figure 4b). During the  
Figure 4: **(a)** NPP variation trend, **(b)** statistical histogram of the NPP dynamic indexes, spatial mapping in **(c)** 2001–2003 and **(d)** 2003–2006. initial period, the NPP of 68% of pixels had a light growth rate of 0%-5%, while a light to moderate reduction of NPP occurred in the central suburb, and central exurb of Guangzhou. During the latter period (Figure 4d), the NPP of 74.6% of pixels in most parts of Guangzhou had a lightly decreasing trend (-5%-0%), and pixels that had a moderate to obvious decreasing trend occurred in the central suburb and the edge between the suburb and the exurb. In addition, the pattern of declining NPP obviously expanded from the suburb to the exurb and expanded from the central exurb to the north exurb. Meanwhile, the NPP dynamic index of decline varied from light to moderate in these regions. [PERSON] [59] pointed out that temporal dynamics of NPP in Guangzhou belonged to a stable type in 1981-2000, but there has been a downward trend from 1991 to 2000.