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Muhammad Kenny Nastution
Journal of Engineering, Infrastructure and Geosciences (2025)
Coastal cities across South and Southeast Asia are sinking faster than the sea is rising, yet planning instruments in many of them still treat inundation as a flooding problem rather than a subsidence problem. This study examined the evidence on land subsidence and tidal flooding in Semarang, Indonesia, and assessed how far that evidence has been absorbed into the city's spatial and development planning. Published measurements from geodetic, interferometric and machine-learning studies were compiled and compared, alongside recorded inundation extents, and the resulting picture was set against global subsidence surveys and against the governance literature on coastal adaptation. Reported subsidence rates for Semarang vary widely across studies, from two to nineteen centimetres per year, but three independent sources converge on six to eleven centimetres per year in the worst-affected coastal districts, a rate that matches or exceeds contemporaneous measurements for Jakarta. Recorded tidal inundation rose from 292.82 hectares in 2020 to 478.85 hectares in 2022. Nearly forty-four per cent of the coastal zone falls in the two highest vulnerability classes. Despite this evidence, subsidence has not been formally designated as a disaster-prone area category in the city's spatial plan. The study argues that the governance gap, rather than the measurement gap, is now the binding constraint, and that the wide dispersion of published rates is itself an obstacle to designation.