Widespread extent of irrecoverable aquifer depletion revealed by
country-wide analysis of land surface subsidence hazard in Iran,
2014–2022, using two component Sentinel-1 InSAR time series
Abstract
Ongoing depletion of Iran’s groundwater, driven by human extraction, has
contributed to 108 incidences of basin-scale land-surface subsidence
covering 29,600 km² (>10 mm/yr,
1.8 %) of the country, 75 % of which
correlates with agriculture. We find Karaj city, neighbouring Iran’s
capital Tehran, is exposed to the steepest surface velocity gradients
(angular distortion, β) caused by differential
subsidence rates, with 23,000 people exposed to ‘high’ subsidence
induced hazard. We further use these velocity gradients to aid
identification of structural and geological controls on surface
velocities of seven of Iran’s most populated cities, identifying
potentially unmapped tectonic faults. We demonstrate that most of Iran’s
subsidence is permanent (inelastic), with the spatial pattern of the
proportion of inelastic deformation potentially depending on geology.
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 41–44 % pre-drought to
31–36 % post-drought. We use automatically processed
short baseline networks of Sentinel-1 Interferometric Synthetic Aperture
Radar (InSAR) data, 2014–2022, to generate and estimate these ground
displacements through time. We correct for atmospheric noise using
weather model data and perform time series analysis in the satellite
line-of-sight direction, serving this data through an open-access online
portal. For each subsidence region, we decompose line-of-sight
velocities into 100 m resolution vertical and horizontal (east-west)
surface velocity fields. We use temporal Independent Component Analysis
to constrain automatically and manually the inelastic and elastic
components of subsidence, respectively.