The growing groundwater crisis in Iran and its impact on land subsidence: A nationwide survey using satellite InSAR

In recent decades, the increasing water demand in Iran has led to extensive groundwater pumping, which has caused significant depletion of many aquifers across the country. This unsustainable extraction has resulted in the loss of groundwater resources and significant land subsidence, adversely affecting several agricultural and urban areas. While previous studies have identified the problem at local scales in major agricultural centers and metropolitan areas, the extent of land subsidence and its impact on groundwater resources, population, and infrastructure across the country is still unknown. This study aims to fill this gap by extending the monitoring and providing a comprehensive understanding of the issue through a nationwide survey that employs Interferometric Synthetic Aperture Radar (InSAR). We generate a large stack of small baseline interferograms at a spatial resolution of 100 meters. Assuming land subsidence is spatially localized and temporally correlated, we remove other signals, mainly from atmospheric phase delay, to isolate the subsidence. Our analysis of Sentinel-1 data from 2014 to the present has enabled us to map the subsidence rates across the country. Our findings indicate that over 50,000 sq. km of the country's land is experiencing significant land subsidence, primarily in agricultural areas, but also in urban areas. As this subsidence is associated with pumping from confined aquifers, we estimate an annual groundwater loss of almost 2 Billion Cubic Meters in Iran, which is in agreement with independent in-situ measurements and GRACE data. By combining our estimated groundwater loss with a land cover map and official agricultural production data, we explore how inefficient irrigation in certain parts of the country is the main driver of groundwater loss. Our study underscores the urgent need for immediate measures to address the issue of groundwater loss in Iran and mitigate its effects on the country's population and infrastructure.