## 4 Discussion  
### Inconsistency between Greenness and Productivity and Its Potential Reasons  
Previous studies mainly discussed vegetation dynamics using a single index, ignoring the difference between vegetation greenness and productivity. Our findings revealed a marked inconsistency between them across different agglomerations. In BTH, only 69.87% of the area exhibited concurrent changes in both greenness and productivity, while the corresponding figures for the YRD and PRD were lower, at 42.93% and 45.65%, respectively (Figure 4). The regions where these consistent changes occurred were primarily concen  
Figure 6: Dynamics of rainfall, solar radiation, and temperature from 2001 to 2020.  
Figure 7: The impact of climatic factors on vegetation greenness and productivity.  
trated in areas without land use change. This alignment was further supported by the overlap ratios, which indicated that 87.45% of the consistent change areas in BTH, 79.31% in the YRD, and 77.48% in the PRD correspond to regions without land use change. On the other hand, the areas that exhibited inconsistent changes were distributed within both the regions with and without land use changes. This inconsistency could be attributed to factors including land use change and climate change [41; 42; 43].  
The impact of land use change on the inconsistency between greenness and productivity can be preliminary explored by comparing their dynamics in the regions with and without land use changes. From 2001 to 2020, both greenness and productivity showed a rising trend in the regions without land use change. A notable observation was that the increase rate in productivity exceeded that of greenness, particularly in land use types such as cropland and grassland. The reason for this difference might be that as vegetation matures, the change rate in greenness tends to decelerate in the later stages of growth; conversely, the photosynthesis capacity of vegetation gradually enhances, leading to an accelerated increase in productivity [41]. In the regions with land use change, the responses of greenness and productivity also varied. The transformation of green land into construction land, for example, exerted a more profound negative influence on greenness than on productivity across all agglomerations. This is likely due to the direct removal of vegetative cover during urbanization, which significantly reduces greenness, while residual vegetation may still maintain some level of productivity [44].  
Climate change also plays a role in the inconsistency between greenness and productivity [16]. Different climatic factors have varying degrees of influence and often have contrasting effects on greenness and productivity. For example, increased rainfall may enhance greenness by promoting vegetation growth, but excessive rainfall can also lead to flooding and other negative impacts on productivity [26; 45]. Similarly, temperature changes can affect both greenness and productivity, but their specific impacts depend on the species and ecological niche of the vegetation [46].  
Vegetation greenness is a canopy structural property that has a close linkage with photosynthetic capability [47; 48]. Previous studies widely applied vegetation greenness as a proxy to analyze vegetation productivity dynamics [49; 50]. Some studies even attempted to estimate vegetation productivity directly based solely on greenness, without relying on additional data [51]. Our study revealed the inconsistency between greenness and productivity, and pointed out that climate change and land use change affect them differently. Greenness primarily reflects the structural properties of the vegetation canopy, while productivity is a measure of the vegetation's ability to convert solar energy into biomass [52]. Thus, it is necessary to clarify the differences between vegetation greenness and productivity in further research to explore vegetation dynamics in a scientific way [53].