Land surface parameterization schemes in climate models

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Land surface parameterization schemes in climate
models

• Bart van den Hurk
• (KNMI/IMAU)

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The global energy budget
Trenberth, 2009
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The global hydrological cycle

• residence time
• in atmosphere 10 days
• in ocean 3000 yrs
• land 1-5 yrs

Peixoto Oort, 1992
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The global carbon budget
IPCC, 2007
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General setup of General Circulation Models (1)

• What determines the evolution of the atmosphere?
• Motion
• Equation of motion
• U, V f (pressure gradient, friction)
• Temperature
• Conservation of energy
• T f (thermodynamics, radiation)
• Moisture content
• Conservation of mass
• q f (evaporation, condensation)

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General setup of General Circulation Models (2)

• Basic equations are solved on a grid
• Computational constraints
• Typically 100-500 km horizontal
• 1 ? 1 65,000 surface points
• Typically 20-50 vertical layers
• 1 5 million grid points
• Numerical constraints
• Numerical stability limits time step of
  integraton
• 10 60 minutes/time step
• One year 105 time steps, one century 107

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General setup of General Circulation Models (3)
Land treatment in GCMs
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General setup of General Circulation Models (3)

• Many processes are sub-grid, and need to be
  parameterized
• Fine scale processes (fluxes) expressed in terms
  of resolved variables (mean state) using (semi-)
  empirical, observation based equations
• Example turbulent sensible heat flux

?a
?a
H
H Sensible heat flux W/m2 ? air density
kg/m3 cp specific heat J/kg K U wind
speed m/s CH exchange coefficient - ?s - ?a
temperature gradient K
?s
?s
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Parameterizations in GCMs

• Examples
• Radiation
• Condensation/cloud formation
• Convection
• Turbulent mixing
• Land surface processes

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Landprocesses in atmospheric models

• Energy-budget
• Albedo

Surface Albedo Dark forest 9-12 Grassland 15-2
0 Bare soil 20-30 Snow in forest 15-25 Open
snow 50-85
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Landprocesses in atmospheric models

• Energy-budget
• Albedo
• Evaporative fraction

Surface LE/Q Boreal forest 25 Forest in
temperate climate 65 Dry vineyard 20 Irrigate
d field in dry area 100
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Landprocesses in atmospheric models

• Energy-budget
• Albedo
• Evaporative fraction
• Water budget
• Runoff-fraction

P
LE
Direct runoff
Infiltration
Drainage
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Landprocesses in atmospheric models

• Energy-budget
• Albedo
• Evaporative fraction
• Water budget
• Runoff-fraction
• Soil water reservoir

Deep rootzone
Shallow rootzone
Season
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Landprocesses in atmospheric models

• Energy-budget
• Albedo
• Evaporative fraction
• Water budget
• Runoff-fraction
• Soil water reservoir
• Carbon budget

CO2
H2O
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Fluxnet data analysis

• Fluxnet collection of ground stations worldwide
  over various surface types

Teuling et al, 2010
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General form of land surface schemes

• Energy balance equation
• K?(1 a) L? L? ?E H G
• Water balance equation
• ?W/?t P E Rs D

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General form of land surface schemes

• Energy balance equation
• K?(1 a) L? L? ?E H G
• Water balance equation
• ?W/?t P E Rs D
• Coupled via the evaporation

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Development history of land schemes

• Late 1960s bucket scheme (Manabe, 1969) with
  depth of the reservoir 15cm

P
E
Direct runoff
E (W/Wmax) Epot
R 0 (WltWmax) R P LE (W?Wmax)
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Development history of land schemes

• Mid 1970s explicit treatment of vegetation
  (Penman-Monteith big leaf)
• To be combined with submodel for soil
  infiltration/runoff

P
E
Direct runoff
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First Soil-Vegetation-Atmosphere Scheme (SVAT)

• Deardorff (1978) combined
• Penman-Monteith
• Partial vegetation coverage, but still one energy
  balance equation (lumped surface types)
• effective surface resistance (interpolating
  between canopy value for full vegetation, and
  large value for bare ground)

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First Soil-Vegetation-Atmosphere Scheme (SVAT)

• Deardorff (1978) combined
• Interception of snow and precipitation by leaves
• (small) bucket equation
• Prognostic equation for soil temperature and
  moisture (force restore)

dWl/dt P E (Wl lt Wlmax) dWl/dt 0 (Wl ?
Wlmax) Wlmax c LAI (c 0.2 mm) E Epot I
P E dWl/dt
dW1/dt (C1/z1) I C2 (W Wequ)/? dW/dt I/z2
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Explicit multi-component SVATs

• Separate treatment of vegetation and
  understory/bare ground (Shuttleworth et al, 1988)
• canopy resistance
• evap. resistance for bare ground
• Complex rewriting of PM, involving
• separate net radiation for two components
• solution of T,q within canopy (at network node)
• separate aerodynamic coupling of two components
• Evaporation at bare ground affects canopy
  transpiration and vice versa

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Tiled scheme

• For instance ECMWF (2000)
• Multiple fractions (tiles)
• vegetation (transpiration)
• bare ground (evaporation)
• interception/skin reservoir (pot. evaporation)
• snow (sublimation)
• Multi-layer soil
• diffusion
• gravity flow
• Explicit root profile

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More on the canopy resistance

• Active regulation of evaporation via
  stomatal aperture
• Two different approaches
• Empirical (Jarvis-Stewart)
• rc (rc,min/LAI) f(K?) f(D) f(W) f(T)
• (Semi)physiological, by modelling photosynthesis
• An ? f(W) ?CO2 / rc
• An f(K?, CO2)
• ?CO2 f(D)

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Summary of development

• Soil hydrology
• single bucket
• two-layer force restore
• multi-layer diffusion/gravity flow
• Evaporation from surface
• E b Epot
• PM big leaf (effective rc)
• PM multi-source
• Tiling
• Canopy resistance
• constant
• empirical dependence on environment
• photosynthesis-based

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Some other developments

• Replace lat/lon grid by sub-catchment as spatial
  unit (Koster et al, 1996)
• Explicit parameterization of surface runoff
  (Dumenil Todini, 1992)

Infiltration curve (dep on W and orograpy)
Surface runoff
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Carbon allocation

• Carbon allocation
• distribution over leaf, stems, roots
• decay and cycling through soil

GPP 120
GPP Gross Primary Production NPP Net Primary
Production AR Autotrophic Respiration HR
Heterotrophic Respiration C Combustion
C 4
AR 60
HR 55
NPP 60
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Other biochemical processes

• Nitrogen cycle
• Land use change

http//www.visionlearning.com/library/module_viewe
r.php?mid98
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International comparison/ evaluation experiments

• Project for Intercomparison of Land-surface
  Parameterization Schemes (PILPS Pitman et al)
• Observed atmospheric forcing
• Comparison between partitioning of energy and
  water
• Single site (e.g. Cabauw)
• 2D catchments (e.g. Sweden)

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International comparison/ evaluation experiments

• Global Soil Wetness Project (GSWP)
• Global 2D
• Forcing from satellite, in situ and
  meteorological (re)analysis data
• Latest version 10 yrs (GSWP2) 3 yrs spin-up

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International comparison/ evaluation experiments

• Atmospheric Model Intercomparison Project (AMIP)
• Comparison of land surface processes in multiple
  GCMs
• Forcing is not similar for all models

abs soil moisture content
soil moisture anomaly
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Orders of magnitude

• Estimate the energy balance of a given surface
  type
• What surface?
• What annual cycle?
• How much net radiation?
• What is the Bowen ratio (H/LE)?
• How much soil heat storage?
• Is this the complete energy balance?
• The same for the water balance
• How much precipitation?
• How much evaporation?
• How much runoff?
• How deep is the annual cycle of soil storage?
• And the snow reservoir?

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More information

• www.knmi.nl/hurkvd
• hurkvd_at_knmi.nl