Understanding the Effect of Seasonal Climate Variability on the Salinity in Unsaturated Agricultural Soil

Abstract

Salinization/desalinization processes in the soil vadose zone are important to define agricultural irrigation and drainage schedules, especially in reclaimed crop areas. Numerical modeling of soil–climate interaction is a very helpful tool to understand soil salinity distribution and solute transport and therefore define efficient desalination solutions. A finite element analysis program Code_Bright was used to perform a coupled thermo-chemo-hydraulic analysis aiming at investigating the effect of climate actions on the distribution of soil salinity in depth, by modeling solute transport in the vadose zone under fresh/saline groundwater supply. The analysis separated first the effect of rain infiltration and evaporation, and then a real climate was considered as the boundary condition. A downward flow pattern induced by rainfall in the unsaturated zone resulted in a nonlinear salt leaching process. Significant differences in salt concentration between the surface and lower layer caused by rainfall resulted in a decrement in the leaching efficiency. Evaporation causes water to move upward and salt transport to the surface, thus enhancing the soil salinity above the evaporation front. The salinity above the groundwater table and below the evaporation front were less affected regardless of the salinity of the supplied groundwater. The model simulated the salt leaching process during the wet seasons and salt accumulation processes during the dry ones. The soil salinity and saturation at the soil surface have significantly responded to seasonal climate variability. A typical seasonal climate variability would result in a low salt leaching efficiency through years in the coastal reclamation area. These results would be helpful for the design of soil salinization management strategies, such as reducing salt accumulation by reducing evaporation or leaching the surface salt in the dry season, and increasing the drainage to promote leaching in the wet season.