Research Highlights

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

by Ph.D. Student: Estelle Chaussard


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.

Indondesia

Figure 1. Map of the population density in western Indonesia from the 2000 census. Cities with over 1 million inhabitants are marked by green squares; province capitals are shown with dark blue contoured squares. The distribution of compressible deposits is shown with the black line: the deposits are observed from the coast to the black contour or within the back contour. The area defined by the red line shows the InSAR ALOS data coverage available from the Alaska Satellite Facility.


Indondesia

Figure 2. Averaged 2006–2009 LOS velocity map of Sumatra, Java, and Bali, Indonesia, from ALOS InSAR time-series analysis, overlaying SRTM V4 DEM. Insets: zoom into the subsiding areas. The emplacement of major cities are shown by black diamonds and labeled for reference. The color scale shows red colors as negative LOS velocities (subsidence) and blue colors as positive LOS velocities (uplift). Vertical subsidence rates converted from the LOS rates are labeled on the color scale.



Reference:

Chaussard, E., Amelung, F., Abidin, Hasanudin., and S.H., Hong (2012), Remote Sensing of Environment Vol. 128, pp. 150–161.