Update on LMWG Proposed Hydrologic Improvements to CLM

1. Update on LMWG Proposed Hydrologic Improvements to CLM Project Objectives:Wetter soils, increased transpiration/photosynthesis, improved partitioning of evapotranspiration and representation of land-atmosphere feedbacks, particularly in the tropics (Amazon) • Overview of proposed hydrology schemes (3) • CAM/CLM and offline CLM simulations – Follow the water • Preliminary conclusions • Validation against tower fluxes

2. CLM Hydrology Project Simulations

3. Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage Ocean Summary of Hyd_dlptmcs (NCAR) Interception (decrease) – Reduce fraction of potential intercepted water by ¼. Transpiration (increase) –Soil moisture stress as in LSM (linear function between optimum and dry soil moisture). Soil Evaporation (decrease) – Reduce soil-canopy air space conductance. Surface Runoff (decrease) – Saturated fraction runoff unchanged. Runoff over non-saturated fraction controlled by enhancement factor based on root fraction in top 3 layers (macropores). Soil Water Dynamics (increase) – Remove exponential decrease in hydraulic conductivity. Depends only on sand content of each layer. Drainage (increase) – Eliminate saturated and non-saturated fraction drainage. Free drainage from layer 10 controlled by hydraulic conductivity. Note that Infiltration is a residual of surface water flux - evaporation - surface runoff.

4. Ocean Summary of Hyd_bd_nlai (GIT) Interception (decrease) – Limit storage capacity and leaf wet fraction by fractional area of liquid precipitation (convective rain falls over 10% of gridcell). Surface Runoff (decrease) – Saturated fraction runoff is exponential function of existing water table scale height. No non-saturated fraction runoff. Soil Water Dynamics (increase) – Remove exponential decrease in hydraulic conductivity. Depends only on sand content of each layer. Drainage (increase) – Eliminate saturated and non-saturated fraction drainage. No flux boundary condition at bottom layer. Base flow consists of weighted contributions of freely draining soil and that impeded by coupling to water table and applied to bottom layer . Water table depth based on lowest saturated layer and soil matric potential. Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

5. Ocean Summary of Hyd_nli Interception (decrease) – Reduce fraction of potential intercepted water by fractional area of precipitation (convective precip falls over 10% of gridcell). Leaf wet fraction unchanged. Applied to convective snow as well. Surface Runoff (decrease) – Saturated fraction runoff is exponential function of water table depth. Max saturated runoff provided by topographic index. Soil Water Dynamics (increase) – Exponential decrease in hydraulic conductivity but enhanced by factor of seven. Drainage (increase) – Eliminate saturated and non-saturated fraction drainage. No flux boundary condition at bottom layer. Excessive water above saturation added to above unsaturated layer. Base flow based on maximum baseflow parameter and exponential function of water table depth and applied to all layers. Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

6. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage Ocean

7. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

8. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

9. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

10. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

11. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

12. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

13. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

14. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

15. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

16. CAM3/CLMx - Follow the water Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage

17. CAM3/CLMx Global Land Annual Average

18. River Discharge to Ocean Offline CLM (“Examining the simulated hydrology under biased forcings makes no sense”) CAM3/CLMx Atmospheric forcing courtesy of T.Qian/A. Dai - NCAR

19. Discharge for World’s Top 10 Rivers CAM3/CLMx Offline CLM

20. CAM/CLMx Climate Changes

21. CAM/CLMx Climate Changes

22. CAM3/CLMx

23. CAM3/CLMx Volumetric Soil Moisture

24. Conclusions • All schemes (in combination with sun/shade model and new surface datasets) offer substantial improvements in producing wetter soils, increasingtranspiration and photosynthesis, and improving the partitioning of evapotranspiration. • Hyd_dlptmcs and Hyd_bd_nlai are most similar in terms of partitioning of evapotranspiration and surface runoff ratio. Globally, Hyd_nli has less transpiration and canopy evaporation, more ground evaporation, lower surface runoff ratio than the other two schemes. • All schemes produce reasonable river discharge to ocean compared to observations. • In the Amazon, all schemes improve temperature and precipitation biases and hydrologic cycle. • In general, the three schemes produce similar but small changes in climate. The most notable exceptions to this are: • All schemes produce cooling in Arabian Peninsula and India in DJF (undesirable) with Hyd_nli resulting in the largest cooling • Increase in wet season precipitation in the Amazon in all schemes (desirable) and an enhanced seasonal cycle in the Congo (undesirable). • In JJA, all schemes produce cooling in Europe and near Caspian/Black seas, most of U.S., and Amazon (desirable). All schemes increase positive bias in precipitation in Arabian Peninsula and southern India (undesirable).

25. Conclusions • All schemes require minimal software engineering for implementation and only small changes to documentation (tech note) • All schemes have free parameters that could be “tuned”. • Final optimal scheme will likely consist of some combination of desirable aspects of each scheme. How to determine this requires more testing against observations and a deeper understanding of why each scheme performs as it does.

26. EXTRA SLIDES

27. Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Melt Soil Water Redistribution Drainage Ocean Summary of Hyd_con (CAM3/CLM3) Interception – Fraction of potential intercepted water is an exponential function of leaf and stem area. Transpiration – Soil moisture stress is a non-linear function of root distribution and soil water potential. Soil Evaporation – Soil-canopy air space conductance is a weighted function of bare soil and dense canopy conductances where weights depend on leaf and stem area. Surface Runoff – Sum of runoff from saturated and unsaturated fractions which are determined from a water table scale height (conceptual TOPMODEL). Soil Water Dynamics – Exponential decrease in hydraulic conductivity. Drainage (increase) – Sum of drainage from saturated and non-saturated fractions plus drainage from layer 10 controlled by hydraulic conductivity. Note that Infiltration is a residual of surface water flux - evaporation - surface runoff.

28. ABRACOS CLMx (solid line), Observed (dashed line) Latent Heat Flux (Aug 8-Oct 4, 1992) Broadleaf evergreen tropical forest Hyd_bd_nlai Hyd_dlptmcs Hyd_nli Hyd_con

29. ABRACOS CLMx

30. CLM Forcing and Validation Requirements – Tower Flux Sites • Atmospheric forcing • Magnitude of wind (m s-1) • Specific humidity (kg kg-1) (or relative humidity or dewpoint temperature) • Pressure (Pa) • Air temperature (K) • Incident longwave radiation (W m-2) (or derived from vapor pressure and temp) • Precipitation (mm s-1) • Incident direct and diffuse visible and near-infrared solar radiation (W m-2) (or total solar radiation) • Netcdf format, ½ hour resolution preferred • Surface characteristics • Plant functional types and abundance • Soil color • Soil texture (vertical profile of %sand/%clay) • Monthly LAI and SAI • Monthly canopy top and bottom heights

31. CLM Forcing and Validation Requirements – Tower Flux Sites • Validation • Radiative fluxes (m s-1) • Turbulent fluxes (including CO2) • Soil temperature and soil moisture • Runoff

32. Tower Flux Site Forcing and Validation Data In-house • FIFE (grassland prairie in Kansas) • BOREAS (old aspen, old black spruce in Canadian boreal forest) • Cabauw (grassland in the Netherlands) • Valdai (grassland in Russia) • ABRACOS (rainforest in Brazil) • Tucson (semi-arid desert) • Other possibilities • LBA (primary rainforest, pasture) • FLUXNET (various ecosystems) • Hapex-Mobilhy (soybean field in France)

33. Interception • Hyd_con • Hyd_dlptmcs • Hyd_nli • Hyd_bd_nlai

34. Transpiration (Soil Moisture Stress) • Hyd_con • Hyd_dlptmcs

35. Soil Evaporation • Hyd_con • Hyd_dlptmcs

36. Surface Runoff • Hyd_con • Hyd_dlptmcs • Hyd_nli • Hyd_bd_nlai

37. Soil Water Dynamics (hydraulic conductivity) • Hyd_con • Hyd_dlptmcs • Hyd_nli • Hyd_bd_nlai

38. Drainage • Hyd_con • Hyd_dlptmcs • Hyd_nli • Hyd_bd_nlai

39. Drainage

40. CAM/CLMx Climate Changes

41. CAM/CLMx Climate Changes

42. CCSM Hyd_dlptmcs Climate Changes

43. CCSM Hyd_dlptmcs Climate Changes

44. CAM3/CLMx Hydrology Precipitation Evaporation Interception Canopy Water Transpiration Throughfall Stemflow Sublimation Evaporation Infiltration Surface Runoff Snow Soil Water Redistribution Drainage

45. Mean Annual Cycle of River Flow for Amazon and Congo Offline CLM CAM3/CLMx