Spatiotemporal Characteristics and Hydrogeological–Urban Controls of Surface Deformation in Haikou, China, Revealed by PS/DS-InSAR and Spatial Attribution Analysis

Surface deformation in rapidly urbanizing coastal cities is often shaped by the interplay between hydrogeological setting and development disturbance, yet these controls remain insufficiently constrained in tropical coastal environments. Using 119 ascending Sentinel-1A scenes acquired between September 2020 and August 2025, we derived a high-density line-of-sight (LOS) deformation field over Haikou, China, through the combined use of PS-InSAR and DS-InSAR time-series analysis. The results show pronounced spatial heterogeneity, with negative LOS anomalies concentrated in reclaimed coastal sectors, port-adjacent zones, and Jiangdong New District, where cumulative LOS displacement locally approaches 90 mm. DS-InSAR increased the number of valid observations to 764,573, approximately 2.8 times that of PS-InSAR, and showed good internal consistency with collocated PS estimates (R2 = 0.8048). Positive LOS zones are present but are generally weaker and more spatially diffuse than the major negative anomalies, indicating that the near-zero city-wide mean partly reflects compensation between localized negative and positive signals. Spatial attribution analysis suggests that groundwater type, aquifer water-yield property, and geological zoning provide the main hydrogeological background associated with deformation, whereas human activity intensity, road density, and land-use intensity are associated with stronger negative deformation where hydrogeological conditions are susceptible. Because the dataset is limited to a single ascending viewing geometry, the reported deformation is interpreted as LOS motion rather than a fully resolved vertical subsidence field. These results support a cautiously framed interpretation in which coastal urban deformation in Haikou is hydrogeologically conditioned and development-amplified, providing a basis for targeted monitoring and risk-informed planning in newly developed coastal districts.