Conjunctive Surface-subsurface Flow Modeling for Land Surface Parameterizations
Abstract
The land surface models (LSMs) coupled to both global and regional climate models have evolved to support sophisticated linkages and process interactions with climate models. However, subsurface moisture transport equations in most current LSMs are so simplistic that they consider only vertical mean soil-moisture transport without the significant contribution of lateral and subgrid fluxes. A 3-dimensional (3-D) volume averaged soil-moisture transport (VAST) model based on the Richard's equation is developed to incorporate the lateral flow and subgrid heterogeneity induced by topographic characteristics. Although surface runoff is also one of important components for terrestrial hydrologic cycle, most LSMs simplistically estimate it using soil water budget without any explicit flow routing schemes. Therefore, a fully coupled surface-subsurface flow model is necessary for comprehensive terrestrial hydrologic simulations in LSMs. One of approximated forms of the Saint-Venant equations is the non-inertia diffusion wave (DW) model, which can account for the downstream backwater effect. In this study, we develop a conjunctive model of 1-D DW model for surface flow interacting with 3-D VAST model for subsurface flow. This conjunctive model can explicitly simulate surface runoff due to both rainfall excess and soil-surface saturation. The mixed numerical implementation method is employed for each flow component. 1-D DW model is solved by the MacCormack finite difference scheme with second-order accuracy in both space and time. 3-D VAST model is implemented using a time splitting scheme that an explicit method is used to solve the lateral flow after a fully implicit method for vertical flow. The simulation results show that the lateral and subgrid fluxes play a significant role in total soil-moisture dynamics. Ignoring these new terms can cause significant model errors and consequential unrealistic model parameters for calibration. This conjunctive surface-subsurface flow model will be substituted for the existing soil-moisture transport scheme in a current LSM, the Common Land Model (CLM) that provides a full suite of modeling capability to characterize surface water and energy fluxes.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.H23H..06C
- Keywords:
-
- 1800 HYDROLOGY;
- 1830 Groundwater/surface water interaction;
- 1836 Hydrological cycles and budgets (1218;
- 1655);
- 1843 Land/atmosphere interactions (1218;
- 1631;
- 3322);
- 1847 Modeling