# Spatiotemporal Dynamics of Net Primary Productivity in China's Urban Lands during 1982-2015
## 5 Conclusions  
The NPP in China from 1982 to 2015 had an increasing trend, with an average annual growth of 17.15 Tg C, and the turning point of China's NPP trend was found in 1997. The increasing rate of the NPP was 9.59 Tg C/ yr before 1997 and changed to 8.71 Tg C/yr after 1997. Although the NPP in the Chinese permanent urban lands (urban lands in the 1980s) decreased at \(-\)0.0185 Tg C/yr from 1982 to 2015, NPP had a lower decrease after 1997 than before 1997.  
The BTHUA, the YRDUA, and the PRDUA are the three fastest-growing urban agglomerations in China. In the BTHUA, the NPP in urban lands decreased at \(-\)1.67 g C/m\({}^{2}\)/yr, and showed an increasing trend in the \(\sim\)5 km-20 km buffer zones of urban lands, because the proportion of vegetation in the buffer zones was less affected by urban expansion. The increase in the temperature and the decrease in sunshine duration made positive contributions to the NPP trends. In the YRDUA, the NPP in urban lands decreased slightly faster (\(-\)2.45 g C/m\({}^{2}\)/yr) than in the BTHUA. The decreased rate of NPP slowed down from the 5 km buffer zone to the 15 km buffer zone, and even showed an increasing trend in the 20 km buffer zone. The increasing temperature was the main positive contribution to the NPP trends. From the 5 km buffer zone to the 20 km buffer zone, the rate of vegetation loss became slower, reducing its negative contribution to the NPP trends. In the PRDUA, the NPP decrease rate (\(-\)4.18 g C/m\({}^{2}\)/yr) in urban lands was the fastest among the three urban agglomerations. In addition to the decrease in vegetation, the reduction in sunshine duration also made negative contributions to the NPP trends.  
A series of policies around urban agglomerations delayed the damage to the ecological environment caused by urban expansion. In addition to the reduction in vegetation, the contribution of meteorological variables to the NPP trends cannot be ignored. This study provides a reference for future urban ecological environment prediction and policy formulation.  
Data curation, H.Z., R.S., D.P., Y.W., S.Z., J.Z., J.B. and Q.L.; formal analysis, H.Z., R.S., D.P., Y.H. and X.Y.; funding acquisition, D.P. and R.S.; investigation, H.Z., R.S. and D.P.; methodology, H.Z., R.S. and D.P.; project administration, D.P. and R.S.; resources, D.P., R.S., Y.H. and X.Y.; software, H.Z., Y.W., S.Z., J.Z., J.B. and Q.L.; supervision, R.S. and D.P.; validation, H.Z., R.S., D.P. and Y.W.; visualization, H.Z., D.P., Y.W., S.Z., J.Z., J.B. and Q.L.; writing--original draft, H.Z., R.S. and D.P.; writing--review and editing, H.Z., R.S., D.P. and Y.W. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA19090112), the National Key R&D Program of China (2017 YFA0603002) and the National Key Scientific and Technological Infrastructure project \"Earth System Science Numerical Simulator Facility\" (EarthLab).  
**Institutional Review Board Statement:** \"Not applicable\" for studies not involving humans or animals.  
**Informed Consent Statement:** \"Not applicable\" for studies not involving humans.  
**Data Availability Statement:** The CLUD used in this study are available from the corresponding author upon request. The annual 30-m land use/land cover maps of China for 1980-2015 used in our work can be freely accessed at [[https://zenodo.org/record/3923728](https://zenodo.org/record/3923728)]([https://zenodo.org/record/3923728](https://zenodo.org/record/3923728)). The meteorological station data are obtained from data.cma.cn. The NPP data used in our work can be freely accessed at [[https://zenodo.org/record/3996814](https://zenodo.org/record/3996814)]([https://zenodo.org/record/3996814](https://zenodo.org/record/3996814)).  
**Conflicts of Interest:** The authors declare no conflict of interest.