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Coupling WRF and VIC

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Water balance in current meteorological models is disconnected from important components of the terrestrial water balance, which is simulated by separate hydrological models.  Thus, the hydrosphere is disconnected.  For reliable assessments of the full system response to change, particularly climate change, the water budgets between the meteorological and hydrological models need to be consistently connected. Meteorological models derive their water balances through the Land Surface Model (LSM).  WRF currently uses the NOAS and the Pleim-Xiu LSM’s.  In this work these LSM’s will be replaced by the Variable Infiltration Capacity (VIC) model.  The coupled WRF and VIC will simulate the atmospheric-hydrologic interactions and connect the hydrosphere.

VIC is a macro-scale, grid-based water and energy balance model that produces surface water runoff and base flow (the hydrology) consistent with meteorological inputs.  VIC has been successfully applied in many large river basins with good results.  VIC provides the capability to accurately determine land surface energy and water states.  Vic’s distinguishing hydrologic features are its sub-grid representation of hydrologic variability, based on sub-grid soil properties, land cover, and elevation bands.  Thus, the spatial variability in soil properties and topographic effects allows it to represent observed nonlinear soil moisture dependence of the partitioning of precipitation into direct runoff and infiltrations.  Surface runoff is generated in the upper two layers by a variable infiltration curve, and baseflow is produced from the bottom layer (see figure).  Evapotranspiration from each vegetation cover type (there are 16 classes) is calculated using a Penman-Monteith method.  Evapotranspiration, surface runoff and baseflow are computed for each cover type and summed over all cover types within a grid cell weighted by the fractional area that each cover type occupies.

The WRF and VIC models will be coupled using the coupling strategy of the Community Earth System Model (CESM) of the National Center for Atmospheric Research (NCAR) which is an emerging climate model standard.  The new CESM coupler (CPL7) has a redesigned coupling architecture to manage the models and the communications between them.  The surface water and soil moisture components of VIC provide WRF with soil moisture information.  In turn, WRF provides VIC with spatially variable precipitation and temperature.  WRF and VIC have both been configured to work within the coupling system.  The coupled system is currently being implemented and tested.

Variable Infiltration Capacity Macroscale Hydrologic Model
Developed at the University of Washington

Contacts: Robin Dennis

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