Introducing lateral subsurface flow in permafrost conditions in a distributed land surface scheme
Koudelova Petra (1), Koike Toshio (1)
(1) The University of Tokyo
Frozen soil essentially affects land surface processes influencing, thus, land surface – atmosphere interactions. Frozen soil processes should be incorporated in a land surface scheme, which is used in the Tibetan Plateau, because the Plateau is widely underlain by frozen soil. This study introduces a quasi-3D land surface scheme, which accounts for both vertical and horizontal hydrologic processes associated with frozen soil conditions. The attribute “quasi-3D” expresses an explicit linkage between the vertical and horizontal parts of the model. The model is developed by implementing the land surface scheme (LSS) SiB2, which incorporates a 1-D frozen soil parameterization (FSP), in a Distributed Hydrologic Model (DHM).
The SiB2 is embedded into the framework of the DHM and solves all of the vertical processes for each grid cell individually using the meteorological forcing data. The FSP, implemented in the SiB2, is based on approximation Stefan solution and predicts frozen/thawed depth and phase changes of soil water content. Since hydraulic conductivity of frozen soil is highly limited, a saturated zone above the frozen table may occur, which consequently causes subsurface saturated flow above the frozen table. In the model, the SiB2 generates the saturated zone above the frozen table and surface runoff, which are then treated by the saturated zone and the surface flow components of the DHM. The resolution of the three soil layers in the original SiB2 is too coarse for the prediction of saturated zone. Therefore, the soil model is modified into a multi-layer system in this study. 2-D subsurface saturated flow scheme is based on the groundwater component of the DHM, which employs a non-steady Boussinesq equation. The growth/drop of water head due to the saturated flow is converted into the increase/decrease of liquid soil moisture content in the affected layers. The updated values of soil moisture are used as initial conditions for the next time step in SiB2.
A numerical experiment is carried out to demonstrate the effect of surface and subsurface lateral flows on a local water budget in hilly permafrost regions. For this purpose, a small catchment is set up following the real terrain of an experimental slope in the eastern Tibet (GAME-Tibet Mesoscale Experiment Area). Due to the lack of the observation of soil moisture and temperature, two hypothetical scenarios of initial conditions are investigated focusing on evolution of the active layer, soil moisture content and energy surface fluxes. The results suggest a remarkable effect of lateral flow.
Submittal Information
Name :
Date :
Koudelova Petra
30-Jul-04-12:02:53
Organization :
Theme :
The University of Tokyo
Theme 1
Address :
Presentation :
REEL, Dept. of Civil Engineering, The Univ. of Tokyo, Hongo 3-7-1, Bunkyo-ku 113-8656, Tokyo