Semarang is the capital of Central Java province, located in the northern coast of Java island, Indonesia. Land subsidence in Semarang has been widely reported and its impacts can be seen already in daily life. Based on the estimation from Levelling, Interferometric Synthetic Aperture Radar (InSAR), Microgravity and Global Positioning System (GPS) survey methods, land subsidence with rates of up to about 19 cm/year were observed during the period of 1999 up to 2011. Results derived from GPS since 2008 up to 2011 show that land subsidence in Semarang has spatial and temporal variations, with spatial average rates of about 6 to 7 cm/year and maximum rates that can go up to 14–19 cm/year at certain locations. The northern region of Semarang along the coast exhibits higher rates of subsidence compared to its southern region, and this subsidence is believed to be caused by the combination of natural consolidation of young alluvium soil, groundwater extraction and load of buildings and constructions. The impact of land subsidence in Semarang can be seen in several forms, mainly the wider expansion of (coastal) flooding areas, cracking and damage of buildings and infrastructure, and increased inland sea water intrusion.

Land subsidence is not a new phenomenon for Jakarta and Semarang areas. According to some publications, the value of Jakarta’s subsidence may reach 2-4 meter in certain place. Meanwhile, more than 2 meter of subsidence is taking place in northern part of Semarang. Some techniques are being used to derive land subsidence information in these areas such as repeated leveling measurements, GPS surveys, and InSAR measurements. The impact of land subsidence in Jakarta and Semarang could be seen in several ways, such as sea inundation (“Rob” in Javanese), problem on infrastructures, the wider expansion of flooding areas, etc. Cracking on housing, street, “sinking” on the bridges and dyke, problems on drainage are examples of infrastructures problems due to the land subsidence. Huge costs have already been spent to fixing those infrastructures problems both in Jakarta and Semarang. Since mostly liniear pattern of land subsidence are recognized in both area today and probably in the next years to come, in this case the impact especially on infrastructures are probably will getting worse. Insight look the subsidence impact to the infrastuctures in Jakarta and Semarang area would raisen the concern, and become key for adaptation and mitigation.