Land subsidence rates and their implications for potential land loss in coastal Semarang-Demak

Land subsidence is a significant issue in several major cities on Java Island, Indonesia. The Coastal Semarang Demak region is of particular concern because it experiences a more pronounced and consistent land subsidence rate than other coastal areas. In this study, we used InSAR and GNSS to monitor the surface deformation caused by land subsidence in the northern coastal areas of Semarang City and Demak. We adopted the Small Baseline Subset InSAR (SBAS-InSAR) technique to process Sentinel-1A SAR imagery in the research area from November 2014 to April 2025. Information on surface subsidence can be obtained quickly and accurately, and the advantage of using InSAR technology is its ability to monitor long-term surface subsidence in the coastal areas of northern Java. Mapping was performed using the Google Earth Engine (GEE) to analyze the spatial features of regions susceptible to land loss. An analysis was conducted to ascertain the correlation between regions experiencing land subsidence and those at risk of potential land loss from 2014 to 2024. It was concluded that the potential land loss could reach 1,787 ha. The results also indicate that areas with a high risk of potential land loss are located in zones with relatively high land subsidence, which occurs in Bedono, Gemulak, and Sriwulan.