Effects of Shallow Saline Groundwater Table Depth and Evaporative Flux on Soil Salinity Dynamics using Hydrus-1D

Abstract

Soil salinization is a major environmental problem and critical concern in arid and semiarid regions. Hydrus-1D model was used to simulate effects of shallow saline groundwater table depth and evaporative flux on soil salinity movement in a saline environment. After successful calibration and validation with recorded soil moisture and soil salinity data, the model was used to evaluate two hypothetical scenarios for managing soil salinity, i.e., with 5 groundwater table depths (WTD) (WTD as on 2015, 25% and 50% rise; 25% and 50% decline in WTD based on the 2015 reference depth) and 3 different evaporative flux conditions (25, 50 and 75% reduction in evaporative flux). The model was calibrated, validated and run for scenarios with 2015 weather and WTD condition for the periods of 288 days. During calibration periods, root mean square error (RMSE) value of soil moisture content was 0.023 cm3 cm-3 and for soil salinity was 2.58 dS m-1, while during validation period RMSE of 0.023 cm3 cm-3 and 1.5 dS m-1, respectively, was recorded for soil moisture and soil salinity. Simulation results indicated that summer season (March to May, 60–150 Julian days) is the most important time to control soil salinity in this region. Considerable upward salt movement occurred during this period with 25 and 50% rise in groundwater table depth. Average root zone soil salinity increased by 6 and 12 dS m-1 when WTD raised by 25 and 50%, respectively, but negligible change in soil salinity was observed when groundwater table declined by 25 and 50%. The effective way to control this upward salt movement was reducing evaporative demands. Simulation study indicated that reducing evaporative flux of 25, 50 and 75% reduced profile soil salinity by 3.53, 6.95 and 12.38 dS m-1, respectively, during peak summer period.