Estimation of groundwater storage loss using surface-subsurface hydrologic modeling in an irrigated agricultural region.

In the Mississippi alluvial plain (MAP) area, the demand for groundwater resources from the alluvial aquifer for agricultural irrigation has led to significant reductions in groundwater-level elevation over time. In this study, we use the hydrologic model SWAT + to quantify long-term changes in groundwater storage within the MAP in United States, wherein groundwater is used extensively for irrigation. We apply a linear quantile regression method to perform trend analysis for wet, dry, and average conditions for the 1982-2020 period. The SWAT + model uses the gwflow module to simulate groundwater storage and groundwater-surface water interactions in a physically based spatially distributed manner, with groundwater pumping linked to field-based irrigation demand. Results indicate significant trends in storage and groundwater fluxes. In wet conditions, significant decline trends are noted in groundwater head (-18.0 mm/yr.) and groundwater evapotranspiration (-0.7 mm/yr.). Under dry conditions, trends are in groundwater head (-28.0 mm/yr.), recharge (-5.5 mm/yr.), and groundwater discharge (-5.5 mm/yr.). For average conditions, decreases include groundwater head (-20.6 mm/yr.), recharge (-6 mm/yr.), and groundwater discharge (-9.3 mm/yr.). This underscores the significance of local management solutions.