**4. Discussion**

In this work, a differential interferometric analysis using Sentinel-1 SLC images acquired between January 2018 and January 2020 was conducted, to map the LS in TCP, as well as to investigate the potential and limitations of DInSAR for detecting and monitoring the LS in this region. The detailed interferometric coherence analysis revealed that temporal decorrelation is the major challenge for DInSAR application. The AOI is dominantly covered by different types of vegetation, which is a land surface cover with constantly and rapidly changing scattering properties. Moreover, the recurrent floods are an additional source of coherence degradation in TCP. On the other hand, for the short baseline interferometric pairs, where sufficient coherence remains, the APS effect degraded the accuracy of LOS displacement estimates. Therefore, the conventional DInSAR is not an appropriate approach for LS detection and monitoring in the AOI. However, the successful application of advanced multi-temporal DInSAR approaches is still possible. Here, the simplest of the advanced DInSAR approaches, the DIS approach, was applied.

The DIS results revealed that several zones within the AOI are subsiding. The maximum average LOS displacement rate detected in this study ( −6 cm/yr) corresponded to the area located north of Villahermosa (Pomaca and Saloya 2nd) and the town of Paraíso. Subsiding zones at the west and south limits of the Villahermosa urban area, the major urban area of the AOI, were detected; whereas Villahermosa city center remained stable during the analyzed period. The zone located at the southern limits of the Villahermosa urban area presented an average LOS displacement rate of up to −4 cm/yr. This zone is also characterized by a location close to areas recurrently affected by floods (see Section 3.2). Thus, LS increases the flood vulnerability of this zone. It is estimated that the Villahermosa urban area will increase to about 15 km<sup>2</sup> by 2050, and one of the possible urban expansion scenarios assumes an expansion to south-southeast [88], which will further increase the flood vulnerability of the zone. LS in the Comalcalco urban area was also detected, as well as in localities between Comalcalco and Villahermosa.

Three subsiding zones were identified near hydrocarbon extraction zones: at the western limits of the Villahermosa urban area, and two zones to the west-southwest of Villahermosa, close to the Batería Samaria II and Batería Cactus hydrocarbons extraction zones, suggesting a possible relationship between the hydrocarbon extraction and surface deformation. However, the possible subsidence caused in the rest of the identified subsidence zones is unclear. LS can be the result of natural processes and anthropic activities. Natural causes such as tectonics (except co-seismic displacement) and soil compaction can cause subsidence of a few mm/yr [40,89]. However, the natural characteristics of TCP are not significant triggers of subsidence: the AOI is located far from any active tectonic plate boundaries (e.g., the Pacific margin), and the compaction of fluvial sediments is maintained only in active alluvial plain areas that have not been subjected to direct anthropic modification (mainly the eastern–southeastern part of the AOI). In these areas, floodable geoforms prevail that accumulate sediments in the rainy season and are characterized by the overflow of rivers [90]. The central and west parts of the AOI belong to an inactive fluvio-deltaic plain, which currently does not receive alluvial sediments, due to the dam system in the middle basin of the Grijalva River, protection boards, and drainage systems [89] that control the river and rain water flows. On the other hand, hydrocarbon production is expected to be the main cause of anthropogenic subsidence in the AOI, as it is the main economic activity. The anthropogenic subsidence caused by gas and oil extraction can reach up to tens of cm/yr [44]. Therefore, anthropic activities could be responsible for the detected LOS displacement rates in the AOI. However, for the zones where there is not a direct spatial correlation between the subsiding zones and hydrocarbon extraction zones, it is impossible to draw conclusions about the origin of subsidence, and more investigations are required.
