Monitoring of land subsidence in the city of Recife/Brazil using Sentinel-1 SAR interferometry

One of the main causes of land subsidence in the world is the exploitation of groundwater above the regeneration capacity of the aquifer systems. However, the rapid urban growth in estuarine areas can also contribute to the development of this phenomenon. An example of this occurs in the city of Recife, northeastern Brazil. The municipality is built on an estuarine plain composed of several rivers (Capibaribe, Beberibe, Tejipió), which formation results from the occupation of humid areas and mangroves. In recent decades, the excessive removal of water resources from the subsoil has caused the reduction of more than 100 meters of the deep aquifer piezometric level in some places. The presence of these factors in Recife may contribute to land subsidence. To detect this phenomenon, the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique was used. The dataset consisted of 135 Sentinel-1A Interferometric Wide (IW) Single Look Complex (SLC) images from September 2016 to April 2021. The images were acquired in descending orbits and VV polarization. The results of the PSInSAR analysis reveal that in Recife there are several areas of land subsidence with a rate close to -15 mm/year. The main occurrence of soil settlement is observed in large recently built areas in the west zone, and small areas in the north zone. Minor cases occur in the southern zone due to the exploitation of groundwater. The identification of these land subsidence areas can help in the study of urban drainage to avoid flooding sites and in the adoption of mitigating measures for the suitable use of underground water resources.