Widespread Extent of Irrecoverable Aquifer Depletion Revealed by Country-Wide Analysis of Land Surface Subsidence Hazard in Iran

Abstract

Ongoing depletion of Iran's groundwater, driven by human extraction, has contributed to 106 incidences of basin-scale, land-surface subsidence covering 31,400 km² ($>$10 mm/yr, 1.9%) of the country. We use Sentinel-1 Interferometric Synthetic Aperture Radar time series to map and analyze, for the first time, surface velocities within these subsiding regions in vertical and east-west directions. We find maximum subsidence rates in the vertical direction reach $\sim$340 mm/yr in Rafsanjan, with 77% of subsidence faster than 10 mm/yr correlating with agriculture. We assess the risk posed by differential subsidence to residential populations, estimating that $\sim$650,200 people in Iran are exposed to medium or higher subsidence induced risk caused by steep differential subsidence gradients. We further demonstrate the use of these vertical and east-west velocity gradients in aiding identification of structural and geological controls on subsidence patterns, some of which are not evident on existing fault maps. We use Independent Component Analysis nationwide to separate subsidence deformation sources and demonstrate that most of Iran's rapid subsidence, and thus aquifer compaction, is irreversible, with inelastic deformation contributing at minimum 60% of the observed deformation magnitude. This proportion of deformation which is irreversible varies within and between subsidence regions. During a recent, severe regional drought (2020–2023), we demonstrate the control of precipitation on the elastic, recoverable subsidence deformation magnitude, with the elastic to inelastic deformation ratio falling from 41% to 44% pre-drought to 31%–36%.