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Salma TAFASCA (PhD student)
Supervisors: Agnès DUCHARNE and Christian VALENTIN
Impact of soil texture on simulated hydrology
in ORCHIDEE land surface model
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CESM Land Model Working Group18 June 2019, Boulder
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• Soil hydraulic properties are important in hydrological and land surface models (LSMs)
• There is no global coverage of measured soil hydraulicproperties
• Pedotransfer functions derive soil hydraulic properties fromavailable soil data e.g. soil texture.
Introduction
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Soil texture: relative proportion of sand, silt and clay
What is soil texture?
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2 µm 50 µm 2000 µm
Clay Silt Sand
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Soil texture: relative proportion of sand, silt and clay
What is soil texture?
12 USDA soil textures
% Sand
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2 µm 50 µm 2000 µm
Clay Silt Sand
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Soil texture: relative proportion of sand, silt and clay
2 µm 50 µm 2000 µm
Clay Silt Sand
Soil texture class
Median diameter (µm)
What is soil texture?
12 USDA soil textures
% Sand
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How does soil texture impact simulated hydrology in a LSM?
Soil texture: relative proportion of sand, silt and clay
2 µm 50 µm 2000 µm
Clay Silt Sand
Soil texture class
Median diameter (µm)12 USDA soil textures
% Sand
What is soil texture?
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• State-of-the-art land surface model• Developed by the Institute Pierre Simon Laplace (Paris)• Simulates water, energy and carbon fluxes
The land surface model ORCHIDEE
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• Multi-layer scheme (11 layers)
• Physically based description of soil water fluxes: Richards equation
• Soil thickness: 2m
• Free drainage at the bottom
Rsurf
D
PSoil EvapTransp.
Soil hydrology in ORCHIDEE LSM
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• Multi-layer scheme (11 layers)
• Physically based description of soil water fluxes: Richards equation
• Soil thickness: 2m
• Free drainage at the bottom
Rsurf
D
PSoil EvapTransp.
Requires K(θ) and D(θ) curves:From Van Genuchten equations
Soil hydrodynamic parameters(porosity, Ks, ts…..)
Soil texture
Soil hydrology in ORCHIDEE LSM
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• Multi-layer scheme (11 layers)
• Physically based description of soil water fluxes: Richards equation
• Soil thickness: 2m
• Free drainage at the bottom
Rsurf
D
PSoil EvapTransp.
Requires K(θ) and D(θ) curves:From Van Genuchten equations
Soil hydrodynamic parameters(porosity, Ks, ts…..)
Soil texture
Soil hydrology in ORCHIDEE LSM
K(θ) D(θ)
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Soil texture map Derived soil parameter map
Pedotransfer functions
Reynolds et al. (2000)
Deriving soil parameters in ORCHIDEE LSM
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Soil texture map Derived soil parameter map
Pedotransfer functions
Look-up table ofCarsel and Parrish (1988)
Deriving soil parameters in ORCHIDEE LSM
Reynolds et al. (2000)
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Offline ORCHIDEE simulations
0.5° resolution
Period: 1980-2010
Different soil maps and atmospheric forcings
Soil Map Atmospheric forcing Texture distrib.
Reynolds CRU-NCEP
Reynolds GSWP3
Zobler GSWP3
SoilGrids GSWP3
Uniform Loam GSWP3
Uniform Loamy Sand GSWP3
Uniform Silt GSWP3
Uniform Clay GSWP3
Numerical experiments
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Soil Map Atmospheric forcing Texture distrib.
Reynolds CRU-NCEP
Reynolds GSWP3
Zobler GSWP3
SoilGrids GSWP3
Uniform Loam GSWP3
Uniform Loamy Sand GSWP3
Uniform Silt GSWP3
Uniform Clay GSWP3
Numerical experiments
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Reynolds et al. (2000) Zobler (1987) SoilGrids (Hengl et al., 2014)
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Offline ORCHIDEE simulations
0.5° resolution
Period: 1980-2010
Different soil maps and atmospheric forcings
Soil Map Atmospheric forcing Texture distrib.
Reynolds CRU-NCEP
Reynolds GSWP3
Zobler GSWP3
SoilGrids GSWP3
Uniform Loam GSWP3
Uniform Loamy Sand GSWP3
Uniform Silt GSWP3
Uniform Clay GSWP3
Numerical experiments
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Offline ORCHIDEE simulations
0.5° resolution
Period: 1980-2010
Different soil maps and atmospheric forcings
Soil Map Atmospheric forcing Texture distrib.
Reynolds CRU-NCEP
Reynolds GSWP3
Zobler GSWP3
SoilGrids GSWP3
Uniform Loam GSWP3
Uniform Loamy Sand GSWP3
Uniform Silt GSWP3
Uniform Clay GSWP3
Numerical experiments
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Grid point scale response of ORCHIDEE to different soil textures
Soil Map Atmospheric forcing Texture distrib.
Reynolds GSWP3
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Grid point scale response of ORCHIDEE to different soil textures
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Global scale response of ORCHIDEE to different soil maps
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Different realistic soil mapsSimilar climate forcing
Global scale response of ORCHIDEE to different soil maps
• Similar water budgets for different soil maps.
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Contrasted uniform soil mapsSimilar climate forcing
Global scale response of ORCHIDEE to different soil maps
• Similar water budgets for different soil maps.
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Global scale response of ORCHIDEE to different soil maps
• Similar water budgets for different soil maps.
• Climate forcing impacts more than soil texture.
Similar soil mapDifferent climate forcing
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Estimated total runoff(Rodell et al., 2015)
Estimated ET (Rodell et al., 2015; Jung et al., 2010; Miralles et al., 2011)
• Similar water budgets for different soil maps.
• Climate forcing impacts more than soil texture.
• Differences in water budget smaller thanuncertainty in observations.
Global scale response of ORCHIDEE to different soil maps
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• Similar spatial patterns with Reynolds map and uniform Loam map.
Evapotranspiration (mm/d)
Spatial distribution of simulated water fluxes
Reynolds map Reynolds map
Uniform Loamy map Uniform Loamy map
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• Similar spatial patterns with Reynolds map and uniform Loam map.
• Higher spatial sensitivity of surface runoff to soil maps.
Evapotranspiration (mm/d) Surface runoff (mm/d)
Spatial distribution of simulated water fluxes
Reynolds map Reynolds map
Uniform Loamy map Uniform Loamy map
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Sensitivity of evapotranspiration spatial patterns
Reynolds - Zobler
Grey areas: differences not statisticallysignificant (student t-test, α=5%)
Differences of ET (mm/d)
GSWP3 – CRU-NCEP
SoilGrids – Uniform loam Reynolds – Obs (GLEAM)
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Sensitivity of evapotranspiration spatial patterns
Reynolds - Zobler
Grey areas: differences not statisticallysignificant (student t-test, α=5%)
GSWP3 – CRU-NCEP
SoilGrids – Uniform loam Reynolds – Obs (GLEAM)
Change of soil map
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Sensitivity of evapotranspiration spatial patterns
Reynolds - Zobler
Grey areas: differences not statisticallysignificant (student t-test, α=5%)
GSWP3 – CRU-NCEP
SoilGrids – Uniform loam Reynolds – Obs (GLEAM)
Change of climate forcing
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Sensitivity of evapotranspiration spatial patterns
Reynolds - Zobler
Grey areas: differences not statisticallysignificant (student t-test, α=5%)
GSWP3 – CRU-NCEP
SoilGrids – Uniform loam Reynolds – Obs (GLEAM)
Evapotranspiration bias
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Conclusion and perspectives
• Small scale: realistic sensitivity of ORCHIDEE to soil texture
• Global scale: weak sensitivity of simulated water budget to soil texture maps
compared to other forcings (climate, vegetation …)
• Why?
• Maps of dominant soil texture at 0.5° favoring loam (over 40% overlap)
• Common input soil data (FAO/UNESCO soil map of the world)
• What next?
• Sub-grid variability of soil properties
• Other soil components: organic matter, soil structure
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