Large scale land subsidence of Jakarta Megacity for the last decade

Numerous scientific papers and journals have extensively documented and published findings on the land subsidence phenomenon in Jakarta Megacity. These studies consistently assert that a combination of socio-economic activities and climate change is the primary contributor to this issue. Despite the inherent low-lying topography of Jakarta’s northern part, situated below sea level, there is a discernible trend of land subsidence spreading beyond its natural boundaries to encompass the western and eastern regions.

This post delves into the latest developments in the large-scale land subsidence of Jakarta Megacity, employing an InSAR (Interferometric Synthetic Aperture Radar) analysis based on a pair of Sentinel-1 SAR data.

Data used in the study was captured on November 12, 2015 and used as baseline. While data captured on January 17, 2024 was used as secondary scene. Both datasets were collected in ascending flight direction. Ascending means the satellite is moving from south to north, while descending means the opposite. The orbit direction affects how the SAR images look and how they can be interpreted. For example, ascending images are better for detecting vertical displacements, while descending images are better for detecting horizontal displacements. Ascending and descending refer to the direction of the satellite’s orbit relative to the Earth’s rotation.

Using the ASF data search platform then I produced the vertical displacement. Figure below summarized the data used in the analysis.

Figure below shows the unwarp image, where we can see there are large scale spatial distribution of fringe was detected. Unwarp and fringe are terms related to InSAR analysis, which is a technique to map surface displacement and topography using radar signals. Unwarp refers to the process of recovering the absolute phase difference from the wrapped phase difference, which is limited to a 2π cycle. Fringe refers to the pattern of phase difference that indicates terrain information, similar to a contour map. While phase is the fraction of one complete sine wave cycle of the radar signal. It is determined by the distance between the satellite and the ground targets. By comparing the phase difference between two SAR images of the same area, taken from slightly different positions, InSAR can extract information about the terrain elevation or deformation.

While figure below is the LOS displacement, that represented the land subsidence detected from satellite. LOS displacement is the one-dimensional component of displacement along the line of sight (LOS) between the satellite and the ground. Red color represents land subsidence up to 0.05m while blue color represents uplift up to 0.05m. As we can see, now the land subsidence occurred in the western and eastern part of Jakarta Megacity.

The western part is dominated by large scale industrial areas, while in the eastern part dominated by both, residentials and industrial areas. It seems that combination of over exploitation of ground water and uncontrolled-unmonitored land use land cover resulted these land subsidence.

This will obviously leads to a great negative impact not only for economic but also for human-environment. Serious problems such as flooding, infrastructure damage, coastal erosion, and saltwater intrusion is the result of land subsidence. Some parts of Jakarta are prone to sinking more than others, such as North Jakarta, West Jakarta and East Jakarta.

If you want to understand about satellite-based InSAR you may read this article from Nature. The article discuss briefly how InSAR can be used for daily monitoring of ground motion, land deformation caused by an earthquake, the evolution of the magmatic system during a volcanic crisis, and many more.