Modeling Groundwater Recharge in the Brazos River Alluvium Aquifer (BRAA) using CLM 4.5

Traditional hydrologic modeling has partitioned water cycle into its different component (i.e. rainfall, run-off, or groundwater models). An alternative approach will be described in this research project. Over most of the river alluvium aquifers around the world, those processes are vastly interconnected; therefore, representing them by separated models would not be adequately accurate and, as a consequence, an integrated model (such as a Land Surface Model) would be a solution to assess more than one component simultaneously and reduce the error likelihood associated with estimated boundary conditions. One of these codes is the Community Land Model (CLM) which represents several components related to land biogeophysics, hydrologic cycle, and biogeochemistry; provides the advantage of parallel computing; and examines how these processes affect climate across the world at any temporal scale. A regional scale simulation in the Brazos River Alluvium Aquifer (BRAA) will be performed to compare final results over this area with the Groundwater Availability Model (GAM) report made by the Texas Water Development Board (TWDB) for a 40-years period (1965 to 2004). Previous studies carried on in some parts of the BRAA suggested large variability of recharge rates depending either on the area scientist made their test or the method they selected to obtain their results. Ultimately, USGS estimated a range from 2 to 5 inches per year which could be more reliable. After simulating the BRAA for 40 years, the spatially and historically annual average is close to 3 inches per year which strongly suggest that a LSM such as CLM4.5 could be applied to study hydrologic process in at least a minor aquifer. Several factors affect recharge rates such as irrigation, weather conditions (severe precipitations and drought seasons), soil type, vegetation, or interaction with other aquifers. After running the simulation over the BRAA, we conclude that recharge rates are higher in the south portion of the BRAA than in the norther portion of it. Moreover, results of the remaining parameters we obtained from the CLM4.5 over the BRAA which include net radiation and its components, infiltration, interception and evapotranspiration suggests that there is more solar energy and hydrologic fluxes in the southern portion as well.