## 4 Discussion
Large sections of these areas lie at a relatively lower elevation (\(<\)5 m; Figure 1) and if the current extreme utilization of resources continues unabated, the subsidence rate is expected to increase throughout the 21 st century [14] and this, in turn, could potentially obliterate flood control structures in coastal areas and near inland waterbodies [92]. The impact of subsidence on aggravating floodwater distribution is much more pronounced in coastal areas. The combined effects of severe weather-induced storm surges, subsidence, LULC changes, high tides from tidal forcings, and rises in sea levels can influence the extent of flooding resulting from future landfallingtropical cyclones and other coastal flood regimes, and could incur serious damage to communities and resources in coastal and near-coastal areas. The impact of subsidence on increasing threat of flooding is not limited to coastal areas alone. Low-lying areas proximal to the floodplains of San Jacinto River in the upstream areas experiencing high subsidence rates [91; 93] were identified in this study as being prone to flooding hazards from severe weather events (Figures 3 and 4). The impact is particularly enhanced in the lowland areas, such as near Crosby city and its surrounding areas (elevation <10 m; Figure 7) located along the course of San Jacinto River and bordering (south of) the West Fork San Jacinto watershed (Figure 7). Subsidence rates as high as 20-25 mm/year have been detected in these areas based on historical groundwater decline rates and recent Global Positioning System (GPS) data [93]. In this case, there was a subtle change in elevation gradient from the banks of San Jacinto River outward, heading inland, as shown in Figure 7. Similar to the notion stated earlier, moderate-to-high subsidence rates could change the elevation and orientation of the land surface of the river banks and the gradient of flow during flooding events, potentially affecting wider areas beyond the floodplain boundaries. In summary, the projected rise in sea levels coupled with the land subsidence processes and increasing anthropogenic alterations to the land surface in the coastal areas, and similar processes and activities excluding the rise in sea levels in the inland areas, are expected to exponentially increase the vulnerability of communities and resources in the study area to flooding in the absence of robust resource management and flood resilience and protection strategies. Future works will concentrate on in-depth analysis of the nexus between the rise in sea levels, subsidence processes, and LULC changes in constraining the spatial extent of storm surge flooding in the coastal areas of the project site. Subsidence rates derived from interferometric SAR (InSAR) and calibrated with  
Figure 7: Flooding along the course of the San Jacinto River, particularly affecting the low-lying areas proximal to the course of the flow. ground-based observations will be integrated with elevation data, flood-induced changes detected by SAR, optical imagery, and other relevant datasets to assess the interconnection and significance of these processes on the overall distribution of flooding from storm surges following extreme weather events. Although the approach managed to identify areas that are prone to flood hazards, a number of possible factors and uncertainties could potentially have led to over/underestimation of the extent of the impacted and flood-prone areas. One factor is the possible delay in the time that the Sentinel-1 satellite passed over the affected area. In the event of such a delay, the ground (flood) conditions might have changed by the time of the satellite overpass and thus the SAR image may not truly reflect the surface conditions that resulted from the event.