1. An Overview of the Noah- Distributed Land Surface Model David J. Gochis, Wei Yu, Fei Chen, Kevin Manning WRF Land Surface Modeling Workshop Sep. 13, 2005

2. Brief Rationale for Noah- Distributed Standard land surface parameterizations characterize exchanges of radiation, heat, mass and momentum between the land and atmosphere Historically, treatment of terrestrial hydrology has been simplified 1-d formulations With high resolution implementations/applications there is now a need to explicitly account for enhanced hydrological processes: Violating early assumptions… 1. Surface runoff can not assumed to be “captured” by a stream channel 2. Lateral transfers from one cell may form significant input to adjacent cell

3. Brief Rationale for Noah- Distributed Standard land surface parameterizations characterize exchanges of radiation, heat, mass and momentum between the land and atmosphere Historically, treatment of terrestrial hydrology has been simplified 1-d formulations With high resolution implementations/applications there is now a need to explicitly account for enhanced hydrological processes: –Higher resolution capabilities  land surface heterogeneity –Earth systems-biogeochemcial cycling –Mitigation of “high-impact” weather events (e.g. floods)

4. Outline Brief overview of the Noah LSM Noah-distributed core features Implementation of Noah-distributed into the NCAR/HRLDAS framework Ongoing and planned upgrades to Noah- distributed

6. Community Noah Land Surface Model – Recent Enhancements Recent Enhancement of the Community Noah LSM (released in WRF V2.0, May 2004) ‘Noah-Unified’ –“Nearly”-identical implementations of Noah LSM development effort: NCAR, NCEP, U.S. Air Force Weather Agency, NASA, university community –Fully modularized, F90 code conventions –Seasonal surface emissivity surface emissivity is introduced as function of landuse Added surface emissivity in surface energy balance equation for both snow and non-snow surfaces –Urban model improvements (the simple approach) such as Large roughness length Low surface albedo Large thermal capacity and thermal conductivity

7. Overland Flow Processes in Noah-Router New Parameters: retention depth, surface roughnessNew Parameters: retention depth, surface roughness Ponded water in excess of retention depth subject to overland flowPonded water in excess of retention depth subject to overland flow Overland flow: fully-unsteady, explicit, finite-difference, 2- dimensional diffusive wave (generally applicable to length scales < 1km)Overland flow: fully-unsteady, explicit, finite-difference, 2- dimensional diffusive wave (generally applicable to length scales < 1km) (NCAR Tech Note: Gochis and Chen, 2003) 2-Dimensional Diffusive Wave Overland Flow Routing Ogden, 1997 IF (Surface Head > Retention Depth)  Route Water as Overland Flow

8. Dynamic modeling of land-surface hydrology with ‘Noah-Router’: Ponded Water Processes New Parameters: NoneNew Parameters: None Currently no formulation for partial area coverageCurrently no formulation for partial area coverage Ponded water consists of: residual of ‘infiltration excess’ from previous time step and routed surface waterPonded water consists of: residual of ‘infiltration excess’ from previous time step and routed surface water Direct evaporation of ponded water reduces potential evaporation (no adj. for temp/albedo)Direct evaporation of ponded water reduces potential evaporation (no adj. for temp/albedo) Ponded water not evaporated is subject to infiltrationPonded water not evaporated is subject to infiltration (NCAR Tech Note: Gochis and Chen) Ponded Water Evaporation and Re-infiltration Surface Runoff  Surface Head Direct Evaporation Re-infiltration Issue: May need to revise infiltration formulation when using routed runoff to calibrate: Surface runoff can not assumed to be “captured” by a stream channel

9. Subsurface Flow Routing Noah-Router (NCAR Tech Note: Gochis and Chen) Saturated Subsurface Routing Wigmosta et. al, 1994 Surface Exfiltration from Saturated Soil Columns Lateral Flow from Saturated Soil Layers New Parameters: Lateral K sat, n – exponential decay coefficientNew Parameters: Lateral K sat, n – exponential decay coefficient Critical initialization value: water table depthCritical initialization value: water table depth 8-layer soil model (2m – depth, sealed bottom boundary)8-layer soil model (2m – depth, sealed bottom boundary) Quasi steady-state saturated flow model, 2-d (x-,y-configuration)Quasi steady-state saturated flow model, 2-d (x-,y-configuration) Exfiltration from fully-saturated soil columnsExfiltration from fully-saturated soil columns

10. Noah-Distributed Core Features Present issues in treatment of subsurface routing: –Frozen soil adjustment to soil water Remove soil ice from total soil moisture and route only liquid component –Update of conductivity as a function of soil temp/fraction of frozen soil –Inclusion of variable depth soils

11. Subgrid Routing Noah LSM is run at a variety of grid spacingsNoah LSM is run at a variety of grid spacings Subsurface and overland flow routing need to be performed on a terrain grid (< 1 km)Subsurface and overland flow routing need to be performed on a terrain grid (< 1 km) Required fields are aggregated/disaggregated using a simple averaging schemeRequired fields are aggregated/disaggregated using a simple averaging scheme Soil water, infiltration excess, routing parametersSoil water, infiltration excess, routing parameters Can offer significant computational savings compared to full resolution implementations of Noah LSMCan offer significant computational savings compared to full resolution implementations of Noah LSM Sacrifice detail in current formulationSacrifice detail in current formulation Noah land surface model grid Routing Subgrids AGGFACTR = 4

12. Noah-Distributed Core Features Subgrid disaggregation: proposed new method carrying over weighting factors between LSM model executions Eliminates the “loss” of distributed information between routing time- steps Noah land surface model grid Routing Subgrids

13. Noah-Distributed Software Features F90, up to date with recent version in HRLDAS Routing routines (1-d and 2-d) are contained within a single module (all agg./disagg. Routines will be included into routing module) Routing and sub-grid options are switch-activated though a namelist file Options to output sub-grid state and flux fields to WRF consistent netcdf files Basic Flow: LSM > Disagg. > Subsfc > Overland > Agg. > LSM > …

14. Outline Brief overview of the Noah LSM Noah-distributed core features Implementation of Noah-distributed into the NCAR/HRLDAS framework Ongoing and planned upgrades to Noah- distributed

15. NCAR-HRLDAS (High Res. Land Data Assim. System) Rationale and basics of HRLDAS: –Create globally-deployable variable resolution equilibrated land surface conditions for NWP initializations Current static & forcing data: Time VariableIntervalDatasetGrid ResolutionReference PrecipitationHourlyNEXRAD Stage IV4 kmFulton et al, 1998 Surface MeteorologyHourlyEDAS40 kmRogers et al., 1995 Land UseStaticUSGS-24 Category1 kmLoveland et al., 1995 Greenness FractionMonthlyn/a0.15 degreeGutman and Ignatov, 1998 Soil ClassificationStaticSTASGO-16 Category1 kmMiller and White, 1998 Overland Flow Roughness CoefficientStaticn/aMapped to Land UseAdapted from Vieux, 2001

16. HRLDAS Recent tests over International H2O Project (IHOP) domain 18 month execution 1 Jan, 2001 – 30 Jun, 2002

17. Top Layer Soil Moisture (fraction):

18. Total Column Soil Moisture (mm):

19. Total Surface Evapotranspiration (mm):

20. Ponded Water Evaporation (mm):

24. Outline Brief overview of the Noah LSM Noah-distributed core features Implementation of Noah-distributed into the NCAR/HRLDAS framework Ongoing and planned upgrades to Noah- distributed

25. Future Upgrades to Noah Distributed Improve runtime performance: –2-d vs 1-d formulations DEM-based steepest descent method is much faster Strictly DEM based routing (kinematic) problematic in flat areas where change in sfc water influences flow direction (e.g. backwater) –Working on a compromise algorithm default to DEM based routing check for backwater Perform search –1-d: 129 model days/wall clock d vs. 2-d: 97 model days/wall clock day (~1/3 faster)

26. Future Upgrades to Noah Distributed Complete parallelization Couple to stream channel model (via DESWAT project) Develop better method to nudge/assimilate groundwater and river/stream stage into modeling system Develop enhanced method to characterize stream-aquifer exchange