Sinking cities in Indonesia: ALOS PALSAR detects rapid subsidence due to groundwater and gas extraction

We use interferometric synthetic aperture radar (InSAR) time-series analysis of ALOS L-band SAR data to resolve land subsidence in western Indonesia with high spatial and temporal resolution. The data reveal significant subsidence in nine areas, including six major cities, at rates up to 22 cm/year. Land subsidence is detected near Lhokseumawe, in Medan, Jakarta, Bandung, Blanakan, Pekalongan, Bungbulang, Semarang, and in the Sidoarjo regency. The fastest subsidence occurs in highly populated coastal areas particularly vulnerable to flooding.We correlate the observed subsidence with surface geology and land use. Despite the fact that subsidence is taking place in compressible deposits there is no clear correlation between subsidence and surface geology. In urban areas we find a correlation between rapid, patchy subsidence and industrial land use and elsewhere with agricultural land use. This suggests that the subsidence is primarily caused by ground water extraction for industrial and agricultural use, respectively. We also observe subsidence associated with exploitation of gas fields near Lhokseumawe and in the Sidoarjo regency. A continuation of these high rates of subsidence is likely to put much of the densely populated coastal areas below relative sea level within a few decades.

► Regional InSAR time-series analysis leading to precise mapping of subsidence.
► Nine locations of Indonesia, mainly coastal, are subsiding at rates up to 22 cm/yr.
► Industrial groundwater extraction is responsible for rapid subsidence in cities.
► Elsewhere, agricultural water pumping and gas fields exploitation create subsidence.
► Permanent inundation of the densely populated coastal areas will occur in decades.