## 4 Validation and Discussion of Land Subsidence Results  
### Land Subsidence Results  
Based on the SBAS-InSAR technology, we obtained the average annual deformation rate in some areas of Shanghai from 2016 to 2022 (as is shown in Figure 7). Of the whole monitoring area, the settlement in Shanghai mainly occurred in some coastal areas of PD, BS, MH, and the JS District, showing uneven distribution characteristics, and the maximum annual average settlement rate was \(-\)32.3 mm/a. PD is one of the largest development and construction sites in Shanghai, and the occurrence of a partial settlement in the new economic construction and development zone is inevitable because of the development and construction of large-scale municipal projects. Meanwhile, the increase in population requires more resources including water resources, etc. ; thus, the overexploitation of groundwater will also lead to the occurrence of land subsidence. The JS District exhibits a wide range of regional subsidence, in addition to human influences. It may be that some error points have been selected because of the low coherence. The time series deformation is shown in Figure 8.  
Figure 8 shows the cumulative sedimentation time series from 2016 to 2022. During the 7-year study period, the maximum cumulative settlement in Shanghai was \(-\)188.6 mm, located near Dishui Lake in the PD New Area. The settlement in the main urban area is relatively stable, with a cumulative settlement range of \(-\)40 mm to \(-\)27 mm. The sinking of southern Shanghai has been showing a downward trend. In the coastal area, the settlement near PD Airport is more serious, with a maximum cumulative settlement of \(-\)120 mm. In the cumulative time series, the settlement phenomenon in BS District and JS in the north of Shanghai was the most obvious, and the settlement amount gradually increased as the settlement area gradually expanded. (1) It can be seen from the a-c subgraphs of Figure 8 that the settlement center was already obvious from 17 May 2018. The settlement was mainly distributed in the coastal part of the SJ District and the JS District, and the settlement center was mainly concentrated between approximately \(-\)15 and \(-\)5 mm. Moreover, the maximum cumulative amount was \(-\)50 mm, and the settlement gradually expanded from the JS District to the surroundings. The emergence of a large settlement center near PD Airport may be due to the implementation of the \"Shanghai Airport Special Work Plan for Improving the Normality of Flights\" under the leadership of the municipal government in September 2017. This increased passenger flow, including the improvement of various nearby transportation facilities, resulting in relatively obvious ground subsidence. Figure 7: The average annual ground displacement (**a**) and the standard error (**b**). The purple triangles in the left graph represent selected marked points in the main subsidence areas. (2) It can be seen from Figure 8d-f that the settlement gradually increased on 20 December 2020. The settlement mainly occurred in the JS District and the BS District, and the settlement in and near Shanghai Disneyland in the middle of PD New Area became more obvious. The cause of this settlement was related to human activities, and the maximum cumulative amount was \(-100\) mm. Furthermore, the settlement center was mainly concentrated between approximately \(-30\) and \(-15\) mm. (3) Figure 8g-h show that the settlement area has basically not changed, and on 22 December' 2022, the maximum accumulation in the JS District reached \(-131\) mm, and the cumulative amount in the main settlement center was between approximately \(-40\) and \(-25\) mm. The reason for the settlement of the coastal area of PD New Area is mainly related to its own geological structure; the newly formed land is vulnerable to settlement due to the low degree of consolidation. The corresponding land settlement will be improved, while the consolidation of the land reaches a stable value after a correspondingly long time.