Influence of salt concentration in the drying Lake Urmia on the saltwater intrusion

Study region Lake Urmia and its adjacent coastal aquifer in northwestern Iran, a region that has experienced substantial lake shrinkage over recent decades. Study focus Lake desiccation has increased salinity and water density while lowering lake levels, introducing competing controls on saltwater intrusion into surrounding aquifers. This study quantifies the combined effects of lake level decline and salinity-driven density changes over two decades using a density-dependent SEAWAT model, calibrated and validated against groundwater observations. New hydrological insights for the region Assuming constant lake water density results in a slight advance followed by retreat of the saltwater wedge. In contrast, incorporating observed density increases produces significant wedge expansion, reaching up to 270% of its initial length (from 195 to 540 m) despite a > 6 m decline in lake level. Sensitivity analysis indicated that saltwater intrusion is generally more responsive to changes in groundwater and lake hydraulic heads than to density variations. However, in Lake Urmia, declines in lake level and groundwater level largely counterbalanced each other, reducing the net hydraulic-gradient effect and leaving the increase in lake-water density as the primary driver of wedge expansion. These findings demonstrate that density effects can dominate over hydraulic gradients in shrinking saline lakes under such conditions, accelerating groundwater salinization. The results highlight the necessity of incorporating density variations in modeling and provide critical insight for sustainable groundwater management in arid regions affected by saline lake drying.