1 / 13

Guo-Yue Niu, Zong-Liang Yang, Department of Geological Sciences, Jackson School of Geosciences,

Groundwater impacts on soil moisture simulation. Guo-Yue Niu, Zong-Liang Yang, Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin and Ken Mitchell NCEP CCSM Workshop June 18th, 2008. Problems due to free drainage.

toby
Download Presentation

Guo-Yue Niu, Zong-Liang Yang, Department of Geological Sciences, Jackson School of Geosciences,

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Groundwater impacts on soil moisture simulation Guo-Yue Niu, Zong-Liang Yang, Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin and Ken Mitchell NCEP CCSM Workshop June 18th, 2008

  2. Problems due to free drainage • Total soil water storage: ds/dt = P – E – R • Upper-boundary condition (P – E – Rsur) • Lower-boundary condition ( Rsub) • Redistribution among layers: • Soil hydraulic properties (Ksat, ψsat) • Vertical distribution of roots Problems due to free drainage (GLDAS/Noah) Top 0.4m Top 1.0m Top 2.0m

  3. A simple groundwater model (SIMGM) (Niu et al., 2007) Water storage in an unconfined aquifer: Recharge Rate: • Problems when applied to CLM: too wet soil, possibly due to • Too small recharge rate from soil to aquifer (too small Ka); • Too strong upward flow (too large soil suction, ψbot ); • Too small groundwater dischargeinducing overflow of groundwater to soil

  4. Modifications to SIMGM • Enlarge hydraulic conductivity Ka • Kbot (1 – exp( –f(zwt –zbot) ) / (f(zwt –zbot))  Kbot • Enlarge Rsbmax by e2 = 7.39 (for Noah) • groundwater discharge rate: • Rsb = Rsbmax * exp(–f * zwt) •  Rsb = Rsbmax * exp(–f * (zwt–zbot)) • surface runoff rate: • Rsf = P * Fmax exp(–0.5 * f * zwt) •  Rsf = P * Fmax exp(–0.5 * f * (zwt–zbot)) • Limit upward flow: • Cmic * ψbot Cmic  fraction of micropore content • 0.0 – 1.0 (0.0 ~ free drainage)

  5. Cmic~0 Cmic~1 Capillary Fringe and Soil Pore-Size Distribution See http://www.earthdrx.org/poresizegwflow.html Macropore effects: 1. Larger recharge rate (through macropores) 2. Smaller upward flow (through micropores)

  6. Tests against Sleepers River streamflow data

  7. Soil moisture simulations in Illinois Noah LSM with Noah schemes:Stomatal resistance: Jarvis typeSoil moisture stress factor : soil moistureRoot distribution: 0.0 – 0.4m 85%; 0.4 – 1.0m 15%Micropore fraction: Cmic = 0.5

  8. Noah LSM with CLM schemes Stomatal resistance: Ball-BerrySoil moisture stress factor : metric potentialMicropore degree: Cmic = 0.0 (free drainage) Soil moisture numerical scheme:CLM vs. Noah

  9. Noah LSM with CLM schemes CLM soil moisture numerical schemeSoil moisture stress factor: CLMStomatal resistance: Ball-Berryalso changed s1 = 0.5*(SMC(k)+SMC(min(nsoil,k+1)))/smcmax to s1 = SMC(k)/smcmaxMicropore degree: Cmic = 0.0 vs. Cmic = 0.4

  10. Noah LSM with CLM Schemes CLM soil moisture numerical schemeStomatal resistance: Ball-BerryMicropore degree: Cmic = 0.0 (Free drainage) Soil moisture stress factor: btran CLM vs. BATS

  11. Noah LSM with CLM schemes CLM soil moisture schemeSoil moisture stress factor: BATSStomatal resistance: Ball-BerryMicropore degree:Cmic = 0.0 vs. Cmic = 0.6

  12. Noah LSM with CLM schemes: CLM soil moisture schemeSoil moisture stress factor: BATSStomatal resistance: Ball-BerryMicropore degree: Cmic = 0.62L averaged SM vs. 1L SM to compute hydraulic conductivity

  13. Summary: Groundwater is really important for modeling soil moisture, both for mean-state and variability.We propose to modify SIMGM to account for macropore effects:1. Enlarge recharge rate from soil to aquifer and2. Limit the upward flow from aquifer to soil; and3. Enlarge groundwater discharge rate (to avoid overflow to soil)Cmic is an important calibration parameter and largely depends on surface schemes, e.g., formulations of soil moisture stress factor, although it should depend on deep soil structure. Larger Cmic for larger E at the surface; Smaller Cmic for smaller E at the surface

More Related