## 4 Results and Discussion
### Effects of Changes in Weather and LULC  
Using Equations (5) and (6), the effects of changes in weather and LULC on the NPP of eight land covers were calculated. The average values for effects of weather and LULC change were 0.43 and 0.51, respectively, in 2001-2003, and were 0.45 and 0.48, respectively, in 2003-2006. There were contributions of common interactions for both effects of about 0.06 and 0.07 during the two periods. As stated above, ENSO events clearly affected the weather meteorology variables and thus, impacted the NPP in Guangzhou as well as the global NPP [46]. Despite the overall effects of climate conditions, the effect of the LULC was greater than that of weather variations during both periods, suggesting the significance of LULC as a driving force. Spatial correlation and cluster methods have been used to analyse the quantity and spatial patterns caused by the driving effects at three levels corresponding to slight, moderate and strong variations. A combination of NPP dynamic index and the concerned effects revealed the mechanism of the LULC effects shown in Figure 5. Moreover, the results clearly demonstrated the spatial relationship of the NPP variation response with the driving force at different intensities. As illustrated in Figure 6, obvious spatial cluster scopes and the trend of NPP variation appears in the central area, suburb and exurb under three driving patterns including weather variation dominated, LULC change dominated, and interaction of both effects. The results show that four categories of effects of weather and LULC variation, divided by the area ratio of three levels, show different impacts in the central area, suburb and exurb. When the two effects were under 25% (Figure 5a), both caused similar area ratio (-68%) of NPP slight change which indicates the interactive effects of both slightly affects NPP. Most areas of NPP had a light fluctuation within range of -5% to 5%. Moreover, when the relative effects varied between 25% and 40% (Figure 5b), the NPP area ratio influenced by weather variation during the two periods were 15.1% (-1,120 km\({}^{2}\)) and 27.8% (-2,061 km\({}^{2}\)), respectively, while area ratio affected by LULC change were less than 10%. Therefore, weather variation within range of 25%-40% played a weather-dominated role. NPP dynamic index also focused between -5% and 5%. A similar condition was observed when the relative effects were more than 85% (Figure 5d). It was demonstrated that a slight fluctuation in larger areas caused by interactive effects or the weather-dominated effects was common. As shown in Figure 6, spatial patterns of these areas were weather in the border between suburb and exurb, and with the passage of time, the influence scope was wider in suburb as opposed to that in exurb. When the effects dropped into the 40%-85% range (Figure 5c), NPP affected by LULC change mainly had a lightly increasing and decreasing trend with the area ratio about 67.8% and 73.1% during both two periods, respectively. So, the effects within the 40%-85% range were mainly dominated by LULC change. These variations obviously assembled in the suburb in the initial period (Figure 6b), and then in the exurb in the latter period (Figure 6d). The distinct development from the suburb to exurb was consistent with the urban sprawl trend. In this outward process as shown in Figure 2c, LULC change in some areas of the exurb caused NPP degradation from the slight decreasing (ratio of \(-\)5%-0) to the moderate decreasing (ratio of \(-\)15%-5%) during the two periods. In general, the decrease of NPP suggested the land degradation, while the increase of NPP reflected the vegetation restoration [15,30,38]. Therefore, with the effects being varied within 25%-40%, weather variation played the main role in NPP and mainly caused slight land degradation in the suburb in the early stage. LULC change with its effects above 40% dominated the results that the obvious land degradation happened from the suburb to the exurb in the urban outward expansion.