Reed M. Maxwell 1 , Stefan J. Kollet 1 , Qingyun Duan 1 and Fotini K. Chow 2

1. A dynamically-coupled groundwater, land surface and regional climate model to predict seasonal watershed flow and groundwater response Reed M. Maxwell1, Stefan J. Kollet1, Qingyun Duan1 and Fotini K. Chow2 1Atmospheric, Earth, and Energy Sciences Dept, Lawrence Livermore National Lab 2Civil and Environmental Engineering Dept, University of California, Berkeley This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. UCRL-PRES-XXXXXX

2. Three talks for the price of one • Brief overview on RC/LS/OF/GW coupled model project underway at LLNL • Some details of a new coupled overland flow-groundwater work (Kollet and Maxwell, 2005) • Example problem that illustrates distributed LS/OF/GW modeling

3. Results of first coupled* model study show important gains resulting from process feedback Coupled Model provides much more accurate predictions of: • Runoff • Soil moisture • Water balance Observations -1 Coupled Uncoupled *Maxwell and Miller, J. Hydromet,6(3), 2005. Others have shown similar results.

4. Land surface model This project integrates four models in a unique way

5. Land surface model Groundwater model This project integrates four models in a unique way

6. Land surface model Overland flow Groundwater model This project integrates four models in a unique way

7. Regional climate model Land surface model Land surface model Overland flow Overland flow Groundwater model This project integrates four models in a unique way

8. Regional climate model Land surface model Land surface model Overland flow Overland flow Groundwater model This project integrates four models in a unique way Explicitly incorporates fluxes at air/land-surface/subsurface interfaces Precipitation/Advection Runoff/Routing Moisture/heat flux Evapotranspiration Infiltration/Seepage

9. Project tasks, details • Run RCM over central US w/ a detailed study area over Little Washita watershed • SGP/ARM site • Data to validate all models (need lots) • P1 run in a nested mode, RCM and GW/LS/OF models uncoupled (control run) • RCM (ARPS) passes LS forcing to coupled model • Coupled model spun up w/ obs, forced by RCM • P2 fully couple models, re-run • Verify that models are coupled and balancing mass and energy • Look at water, heat fluxes across the LS and at weather and weather generating processes

10. Surface contours for 1 km resolution grid, 07/08/99 12 UTC

11. RCM/ARPS Results • Norman Oklahoma sounding comparison 07/08/99, 12 UTC q [g/kg] φ[degrees] θ [K] U [m/s]

12. Sacramento Model Calibration for Little Washita

13. Borehole data used to create 3D geostatistical realization of the subsurface

14. Free-surface overland-flow boundary condition, coupled groundwater overland flow • Lots of motivation for coupled model • Watershed modeling • Climate • Water quality • Most (all?) coupled models rely on interface between SW and GW • “conductance concept” • Hard to find field data to support this • Need for a more general formulation • Desire for parallel model w/ a robust non-linear solver • Integrate into ParFlow • Take advantage of infrastructure Kollet and Maxwell, Advances in Water Resources, in press, 2005.

15. The Conductance Concept

16. New Overland Flow Boundary in ParFlow Kollet & Maxwell, 2005

17. Verification Examples 1D Slope: 200 min rain, 100 min recession 2D Tilted V-Catchment: 90 min rain, 90 min recession Jabar & Mohtar, 2004 Panday & Huyakorn, 2004

18. Simulation Examples II Low-K slab

19. Simulation Examples III Random (Gaussian) Heterogeneity Five Realizations Kgeo = qrain

20. Scaled Parallel Efficiency E(np,p) = T(n,1) / T(np,p)

21. Integrating land surface processes into ParFlow an Example • We add in LS processes (parts of CLM) into ParFlow • Hydro, Runoff handled by PF as detailed earlier • Fully distributed • Fully parallel • Use a well-resolved, large scale 2D “Classic” Example problem to investigate coupled model performance and behavior • Dx=100m; Dz=2m; 40km x 0.54km domain • Toth Problem: sinusoidal topography in a large basin • J. Toth, 1963. A theoretical analysis of groundwater flow in small drainage basins. J. Geophys. Research 68:4795-4842. • Forced uniformly with PILPS midlatitude for one year

22. Toth problem uses an sinusoidal topography July Pressure Initial Pressure

23. Coupled model forced by PILPS midlatitude, produces realistic looking hydrograph

24. Averaged, Cumulative ET

25. Distributed Ground Surface Temperature Non-uniform freezing Distribution of temps, non-uniform water content Non-uniform thaw Initialization

26. Distributed Water and Heat Fluxes

27. Summary • We are working on lots of stuff, but have a lot yet to do • Coupled RC/LS/OF/GW project in Y1/control run phase, soon will start dynamic coupling • Coupled overland flow and groundwater method looks very promising • Integrating LS processes into GW provides interesting distributed results need to compare to field site (Little Washita, Valdai) • Still overall question regarding quantifying impacts and scale of coupled processes