**4. Conclusions**

This study constructed a green development SD model for the Chengdu-Chongqing City Group and set five simulation scenarios under the SSPs. The future green development level and the guideline level of each city and of the overall Chengdu-Chongqing City Group were simulated and calculated, with the comparison and analysis of the changes, obtaining the following main conclusions:


Based on these findings, the Chengdu-Chongqing City Group should follow suitable pathways for future development. Specifically, SSP2 should be used as the basis for development until 2025, which entails the continuance of the current development trend, after which a transition should be gradually performed toward SSP1, which should be completed before 2035 to achieve real sustainable development. Afterwards, the Chengdu-Chongqing City Group should continue to develop according to SSP1 from 2035 to 2050.

**Author Contributions:** Conceptualization, Y.L., L.Z., M.L. and Y.X.; writing—original draft preparation, Y.L. and M.L.; writing—review and editing, L.Z. and Y.X.; supervision, L.Z. and Y.X.; funding acquisition, Y.X. and J.X. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research is supported by the National Natural Science Foundation of China (Grant No.41890824, No.52279023).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **Appendix A**

Appendix A shows the historical statistical descriptions of the parameters and the initial values of the state variables of the green development level system dynamics model of the Chengdu-Chongqing City Group constructed in this study, together with the historical test results of the green development level system dynamics model of each city in the Chengdu-Chongqing City Group.

**Table A1.** Statistical description of model parameters in Chengdu and Chongqing.


**Table A2.** Initial values of state variables of the SD model of the green development level of each city in the Chengdu-Chongqing City Group.



**Table A3.** Pass rate of historical test of SD model of the green development level of cities in the Chengdu-Chongqing City Group.

Ten percent pass rate: the ratio of the simulated year to the simulated year for which the relative error between the simulated model value and the historical statistical value is within ±10%; twenty percent pass rate: the ratio of the simulated year to the simulated year for which the relative error between the simulated model value and the historical statistical value is within ±20%.

### **References**

