WRF-VIC: The Flux Coupling Approach
L. Ruby Leung
Pacific Northwest National Laboratory
BioEarth Project Kickoff Meeting
April 11-12, 2011
Pullman, WA
1
What is WRF
WRF is a “community model” that stands for Weather Research and
Forecasting model – a free and shared resource with distributed
development (NCAR, NOAA, AFWA, FAA, NRL, …) and centralized
support (NCAR)
Since version 2.1 (2005), WRF has two dynamical cores: ARW and
NMM – both non-hydrostatic, Eulerian mass, with terrain following
vertical coordinates
Under the NCAR NRCM initiative (2003 – 2008), new features have
been added to WRF for regional climate applications
WRF includes many options for physics parameterizations, including
several land surface models
WRF-Chem includes ‘online’ chemistry to simulate trace gases and
particulates simultaneously with the meteorological fields
PNNL scientists have been major contributors to WRF and WRFChem, including recent implementations of all CAM4 and CAM5
physics for consistency with CCSM
2
What is VIC
VIC is a macroscale hydrologic model that includes features important
for atmosphere-land-vegetation coupling
Parameterize subgrid
variability of precipitation
Infiltration excess runoff
Surface- and groundwater
interactions
Saturation excess runoff
ARNO baseflow curve
3
Hydraulic redistribution
Interactions of water
movement between the root
system and soil porous media
Coupling of VIC with Atmospheric Models
To enable VIC to be coupled to atmospheric models, VIC was
modified from ‘time-before-space’ to ‘space-before-time’ coding
structure (Liang et al. 2006)
MM5 and VIC exchange fluxes through a subroutine call from
MM5 (Fortran) to VIC (C)
Map VIC land surface properties using those defined by the
MM5 preprocessor for Noah LSM
MM5-VIC surface properties and initialization follow the
standard VIC procedures and applied to the North American
monsoon region (Zhu et al. 2009)
Added a groundwater parameterization (Liang et al. 2003) to
simulate surface water – groundwater interactions
MM5-VIC applied to the U.S. at 60 km grid resolution for 1986
– 2002 (Leung et al. 2010)
4
Terrestrial water storage anomaly
Leung et al. (2010)
5
The Flux Coupling Approach
Regional Arctic Coupled Model (RACM) and PNNL iRESM
WRF (v3.2) and VIC (v.4.0.4) have been added to the CESM repository and
communicate with the flux coupler CPL7
VIC surface and subsurface runoff parameterizations added to CLM4
The flux coupling approach allows each model to be applied on its own grids
and be maintained as separate models and utilized different CPUs
GCM/Reanalysis
Ocean (ROMS)
Atmosphere
(WRF/Chem)
Land/Veg/C/N
(CLM/VIC)
Flux Coupler
(CPL7)
Ocean (POP)
6
Atmosphere
(CAM)
RESM
Sea Ice (CSIM)
CESM
Running WRF-VIC
Configure WRF-VIC domain (only tested the same
domain for WRF/VIC with no nesting) using WRF WPS
Generate a mapping file for mapping of fluxes between
WRF and VIC using SCRIP
Create input data for WRF from global reanalysis or
GCMs using WRF WPS
Create data for data ocean (if not coupled with an ocean
model) based on SST from WPS
Create input data for VIC
Soil, vegetation, snowband parameter files based on global 0.05
degree data
Run offline VIC with atmospheric forcing interpolated from 1/8
degree data to generate initial conditions for VIC (e.g., 1-hour time
step, energy mode)
Create VIC initial conditions for WRF-VIC
Compile and run WRF-VIC in the CESM environment
7
Testing of WRF-CLM/VIC
WRF-CLM has been tested using a global domain with CLM input
data available from CCSM
WRF-CLM has also been applied in a regional domain for western
US at 12 km resolution using high resolution CLM data (0.05 degree)
(2003/10 – 2004/9)
WRF-VIC has been tested in a global domain and an Arctic domain
(Chunmei Zhu, UW)
PNNL will test WRF-VIC in a western US or PNW domain
Simulated rainfall from WRF-CLM on
global domain
8
Simulated skin temperature from WRF-CLM on
regional domain
Comparison of observed and WRF-CLM simulated fluxes
Green
Ridge, OR
Tonzi, CA
9
Discussion:
Model domain
Nesting could be a big challenge
Region and resolution
Computational resources and wall clock time
WRF coupling with other components
Online/offline coupling with chemistry (WRF-CMAQ)?
Offline coupling with emission (MEGAN)?
Merging of codes that involve WRF coupled to other components
VIC coupling with other components
Online coupling with managed and unmanaged ecosystems and
biogeochemistry models (CropSyst and RHESSys)
Online coupling with river routing (RHESSys)?
Offline coupling with water management and policy (ColSim)
Merging of codes that involve VIC coupled to other components
Consistency across models
Hydrologic (VIC vs RHESSys) and biogeochemistry components
Code management
10
Common code repository
Central input and output data archive