Objective

1. Modeling the Effects of Groundwater-fed Irrigation on Terrestrial Hydrology over the Conterminous United States Objective • To understand the consequence of groundwater-fed irrigation on groundwater depletion and land surface processes Approach • Incorporated a groundwater pumping scheme into the Community Land Model (CLM4) and applied it in combination with its existing irrigation module • Determined the ratios between surface water and groundwater withdrawals for irrigation using county-level agricultural census • Applied the CLM4 with/without groundwater pumping to continental U.S. to investigate the impacts of groundwater-fed irrigation on local and regional scale water and energy budgets By including groundwater pumping, CLM could better capture the declining groundwater table depth in the Ogallala Aquifer reported by USGS. However, model limitation to capture the magnitude of depletion calls for improvements in the CLM4 subsurface parameterizations. • Impact • Large-scale pumping, currently omitted from most irrigation modeling studies, might greatly alter the hydrologic and land energy fluxes in agricultural regions, and further influence the local and regional climate. • Further development of the groundwater parameterization in CLM4 is needed to effectively represent the two-way interactions between surface water and groundwater, as shown by comparisons between simulations and observations. Leng G, M Huang, Q Tang, H Gao, and LR Leung. 2013. “Modeling the Effects of Groundwater-fed Irrigation on Terrestrial Hydrology over the Conterminous United States.” Journal of Hydrometeorology. DOI:10.1175/JHM-D-13-049.1, in press November 2013.