Evaluation of Recharge and Evapotranspiration Estimation Methods in the Mississippi Alluvial Plain

The Mississippi River Valley alluvial aquifer which underlies the Mississippi Alluvial Plain (MAP) is heavily used for irrigated agriculture and is one of the top three aquifers in the U.S. in terms of groundwater withdrawals for irrigation. Recharge and evapotranspiration (ET) are critical components of the overall water budget in the MAP area. Variations in the magnitude and spatial distribution of these water-budget components due to differing estimation methods could affect the results of the groundwater flow model developed for the Mississippi Embayment Regional Aquifer System (MERAS) used to simulate flow in the MAP area. A comparison of available methods to estimate recharge and ET points out the variability in estimates of these water budget components in the MERAS area. The results for recharge estimates from the PRISM-based calculations used in the original MERAS model are compared to those from the Soil-Water-Balance (SWB) model and from long-term Empirical Water Budget (EWB) estimates. The recharge estimates are examined in areas of differing irrigation intensity, and compared to field-based estimates where available.