HR: 11:20h
AN: H22A-05    [Abstracts]
TI: A Coupled Land-Surface-Groundwater Scheme to Study the Influence of Subsurface Heterogeneity on Mass and Energy fluxes at the Land Surface
AU: * Kollet, S J
EM: kollet2@llnl.gov
AF: Enviromental Science Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AU: Maxwell, R M
EM: maxwell5llnl.gov
AF: Enviromental Science Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 United States
AU: Miller, N L
EM: nlmiller@lbl.gov
AF: Earth Sciences Division, Lawrence Berkeley National Laboratory, 90-1116 One Cyclotron Drive, Berkeley, CA 94720 United States
AB: In this study, we coupled the Community Land Model (CLM) with the fully three-dimensional (3D) variable saturated groundwater flow code Parflow (PF). The coupled scheme, CLM.PF, solves the 2D distributed energy and mass balance equations at the land surface and the 3D Richards equation for a heterogeneous subsurface. The advantages of CLM.PF are quite obvious. Application of this code allows us to assess simplified subsurface parameterizations that are generally used in land-surface models. Also, the impact of the strongly abstracted upper boundary condition (i.e. the land surface) of many widely used groundwater flow codes (e.g. MODFLOW) can be assed using CLM.PF. Here, emphasize is placed on the influence of heterogeneity in the hydraulic properties of the subsurface on the mass and energy fluxes at the land surface. We generate equally likely realizations of the subsurface using transition probability geostatistics and study the ensemble response of the system to spatially uniform atmospheric forcing. Special attention is given to the dependence of land-surface fluxes on the depth and spatial distribution of the free water table, which is not explicitly taken into account by many land-surface schemes. Preliminary results suggest that variable surface fluxes are a direct result of subsurface heterogeneity. The effects of heterogeneity are especially pronounced under dry conditions and heavy precipitation events. The position of the water table naturally depends on the hydraulic properties distribution and plays a key role in the generation of spatially non-uniform surface runoff and evaporation. In the future, CLM.PF will be used in the development of effective or lumped models and in studies of upscaling. This work was conducted under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory (LLNL) under contract W-7405-Eng-48 and Lawrence Berkeley National Laboratory (LBNL) under contract DE-AC03-76F00098.
DE: 1800 HYDROLOGY
DE: 1829 Groundwater hydrology
DE: 1836 Hydrologic budget (1655)
DE: 1860 Runoff and streamflow
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting