Water Table Depth and Soil Salinization: From Pore‐Scale Processes to Field‐Scale Responses

Abstract The accumulation of salts in soils adversely influences plant growth and biological activity resulting in loss of yields and soil ecosystem services. Water table depth plays an important role on solute distribution through the unsaturated zone. We focus on the relationship between saline water evaporation from soil surfaces and water table depths. When the water table was hydraulically connected to the surface, we found more evaporatively driven sodium chloride precipitation at the surface with deeper water tables relative to shallow ones. We attribute this result to lower surface water contents that reach solubility limit sooner and support an expanding salt crust. Thermal imaging confirmed that when surface is hydraulically connected to the water table, capillary flows through the porous precipitated salt maintain the evaporative flux. Macroscopic continuum‐scale numerical simulations demonstrate higher solute concentration closer to the surface in the case of deeper water tables supporting the microscopic picture attributed to fewer evaporation and solute deposition sites at the surface with deeper water tables. Insights from the laboratory‐scale experiments and numerical studies were used to describe soil salinity at much larger scales. We employed two global‐scale databases for topsoil salinity, soil texture, and water table depths to link our laboratory‐scale findings with long‐term and field‐scale observations. The results illustrate the importance of pore‐scale physics and processes on constraining the field‐scale responses.