Studying land subsidence in Yazd province, Iran, by integration of InSAR and levelling measurements

The Yazd-Ardakan plain, located in central Iran, is an arid region with a low rainfall where over-extraction of groundwater for agriculture and industrial purposes has caused serious subsidence in the area. In this study, the small baseline subset (SBAS) algorithm was applied to perform an interferometric synthetic aperture radar (InSAR) time series analysis for the Yazd-Ardakan plain. The result is a space-time deformation product that can be exploited to view not only the smoothly varying long-term surface motion, but also its time-varying patterns. The mean rate of subsidence computed from the repeated first order precise leveling network of Iran was accurately matched by the mean rate of the InSAR time series. Time series analysis of our InSAR mapping suggests that subsidence occurs within a northwest-southeast elliptic-shaped bowl, with peak amplitude of about 120 mm/yr for the 2003-2006 time period. Analysis of piezometric records suggests that subsidence likely results from extensive over-drafting of the aquifer system in the region, which has caused about 16 m of water table decline since 1974. Comparing the subsidence map produced by InSAR and water level change contour allowed the estimation of skeletal storage coefficients, providing a basis for future work that could characterize the storage properties of an aquifer system with a high degree of spatial resolution. The storage coefficient contour map generated in this study simulated the pattern and orientation of the geological structure of the area.