International Journal of Applied Earth Observations and Geoinformation (Dec 2023)
Present-day land subsidence over Semarang revealed by time series InSAR new small baseline subset technique
Abstract
Over the last two decades, Semarang, located in the central region of Java island, Indonesia, has been undergoing significant land subsidence. Mainly attributed to reservoir compaction and fluid extraction, this subsidence has pronounced effects in coastal regions. However, the existing study on the details of subsidence and its application to accurately depict present circumstances has been insufficient. Utilizing the new small baseline subset technique and C-band SAR data from 2015 to 2022, this study delineates the spatial boundaries of land subsidence in Semarang and surrounding areas. Atmospheric effects were mitigated using the GACOS model during InSAR processing. The study reveals dominant vertical movements in Semarang’s north coastal area, characterized by rapid and extensive changes. In contrast, horizontal movement shows relatively small changes in number to the east of the study area. Time series analysis indicates maximum subsidence rate of 100–120 mm/year in the northern and eastern part of Semarang and Demak. Available data from GNSS stations ensures the reliability of these findings. The correlation coefficient of 0.86 indicated substantial association between groundwater and deformation. Approximately 20 % of Semarang’s land area is affected by land subsidence, which is notably more prevalent in alluvial soils and densely populated regions. In Demak, subsidence is primarily observed in agricultural regions, whereas in Kendal, the 50 mm/year subsidence rate represents a growing concern. This accelerating phenomenon poses substantial risks to the local environment and economic sectors. All authorities must harmonize regulations to force their roles, produce details spatial plan maps, and establish mitigation and adaptation infrastructure to handle the current crisis realistically.
