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

a r t i c l e i n f o Keywords: Subsidence Interferometric synthetic aperture radar SBAS time-series Indonesia 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. 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. Lowlands are often densely populated and land use represents a high economic value. The shallow subsurface in these areas frequently contains young, compressible deposits. These soft deposits are particularly vulnerable to subsidence caused by natural compac-tion or anthropogenic activities. While natural compaction is causing slow subsidence in numerous deltas, such as in the Mississippi and Po deltas at 5 and 2 mm/year, respectively (Teatini et al., 2011; Törnqvist et al., 2008), ground water extraction is causing rapid subsidence in urban areas, such as Mexico City and Las Vegas at rates of tens of cm/year (Bell et al., 2002; Cabral-Cano et al., 2008). Subsidence, particularly in combination with sea level rise, heavy rains (such as monsoon), or storms, aggravates inundation risk from the major rivers and widens the coastal areas affected by storm surges and tidal inundation. The costs associated with subsidence are enormous, directly, because of damages to buildings and infra-structures, and indirectly given the increase in flood risk and the threat to human life. Examples of recent flooding events likely amplified by land subsidence include the flooding of New Orleans following Traditional measurements of land subsidence rely on GPS and leveling data. Although these methods provide precise measurements , they are …