ZongLiang Yang

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Introduction to Land Surface Modeling
Zong-Liang Yang The University of Texas at
Austin
Prepared for the TCEQ Meeting May 24,
2006 www.geo.utexas.edu/climate
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Why Land Surface Modeling?

• An important component of the weather, climate or
  environmental system.
• exchanges of momentum, energy, water vapor, CO2,
  VOC, and other trace gases between land surface
  and the overlying atmosphere
• states of land surface (e.g., soil moisture, soil
  temperature, canopy temperature, snow water
  equivalent)
• characteristics of land surface (e.g., roughness,
  albedo, emissivity, soil texture, vegetation
  type, cover extent, leaf area index, and
  seasonality)
• Critical for weather, climate, hydrological, and
  environmental forecasts.

NCAR CLM Website
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The Development of Climate models, Past, Present
and Future
Late 1960s
Early 1980s
Mid 1990s
Present day
Late 2000s?
Mid 1950s
Atmosphere
Atmosphere
Atmosphere
Atmosphere
Atmosphere
Atmosphere
Land surface
Land surface
Land surface
Land surface
Land surface
Ocean sea-ice
Ocean sea-ice
Ocean sea-ice
Ocean sea-ice
Sulphate aerosol
Sulphate aerosol
Sulphate aerosol
Non-sulphate aerosol
Non-sulphate aerosol
Carbon cycle
Carbon cycle
Atmospheric chemistry
Sulphur cycle model
Non-sulphate aerosols
Ocean sea-ice model
Off-line model development Strengthening
colours denote improvements in models
Land carbon cycle model
Carbon cycle model
Ocean carbon cycle model
Atmospheric chemistry
Atmospheric chemistry
John Houghton
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Integrated Environmental Modeling Framework
Climate Change and Variability
Remote Sensing and GIS
Water Resources Applications
Coupled Ocean-Atmosphere Models
Air Quality
Air Quality Models
Mesoscale Models
Soil-Vegetation-Atmosphere Transfer
E
Policy
P
Qs
Hydrologic/Routing Models
D Ss
Qg
D Sg
Ig
In Situ Data
Water Quality and Quantity
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Accurate Land Surface Modeling Is Critical for
Seamless Suite of Forecasts
Boundary Conditions
Initial Conditions
Paul Houser
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Land-Atmosphere Coupling Strength
Koster et al. (2004), Science
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What Are Land Surface Processes

• Land surface processes function as
• lower boundary condition in Atmospheric Models
• Atmospheric Boundary Layer Simulation
• Climate Simulation
• Numerical Weather Prediction
• 4-D Data Assimilation
• upper boundary condition in Hydrological Models
• Water Resources Estimation
• Crop Water Use
• Runoff Simulation
• interface for coupled Atmospheric / Hydrological
  / Ecological Models

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Land Surface Models (LSMs)

• Computer code describing land surface processes
  (also called LSSs, LSPs, SVATs)
• FORTRAN, C, ...
• Tens to thousands of lines
• There are a huge number of LSMs (100 examples in
  literature)
• many are just research models, local-scale
  oriented, with specific process emphasis
• up to 100 canopy, 100 soil, 100 snow, even
  100 atmosphere layers!
• LSMs in GCMs and Hydrological Models are less
  diverse
• one dimensional, with 1-2 canopy, 1-10 soil, 1-10
  snow layers
• three general classes
• Bucket Models (no vegetation canopy)
• Micrometeorological Models (detailed
  soil/snow/canopy processes) Greening
• Intermediate Models (some soil/snow/canopy
  features)

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Four Basic Requirements

• Frequently-sampled (hourly or sub-hourly) weather
  forcing data to drive LSMs
• precipitation (rate coverage, large-scale/convect
  ive)
• radiation (shortwave, longwave)
• temperature
• wind components (u, v)
• specific humidity
• surface pressure
• Initialization of state variables
• soil moisture (liquid, frozen)
• deep soil temperature
• Specification of surface characteristics
• vegetation cover percent and composition (ET,
  BVOC)
• soil type (soil moisture hydrology)
• topography (hydrology)
• albedo (solar radiation energy balance)
• roughness (turbulence momentum exchange)
• root depth (water holding capacity hydrology)
• Validation of simulations of state variables and
  fluxes
• soil moisture

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Best Known Examples

• Biosphere-Atmosphere Transfer Scheme (BATS)
• Simple Biosphere Model (SiB)
• Community Land Model (CLM)
• Noah

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Community Land Model
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Community Land Model Dynamic Vegetation
Ecosystem Carbon Balance
Vegetation Dynamics
Photosynthesis
Growth Respiration
?g CO2?g-1?s-1
Autotrophic Respiration
?g CO2?g-1?s-1
Litterfall
Heterotrophic Respiration
?g CO2?g-1?s-1
Nutrient Uptake
NCAR CLM Website
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Noah
NCEP Noah Website
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Research Issues

• Obtaining and applying relevant pure biome data
  to test or calibrate LSMs
• Dealing with spatial/temporal heterogeneity
• area-average parameters or tiling of land covers?
• defining space-time structure of atmospheric
  inputs
• Making best use of remote sensing data for
  initialization, specification and validation
• Improving key processes
• Snow/Frozen soil
• Runoff generation/routing
• Greening of LSMs (carbon balance and vegetation
  dynamics)
• Urban

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CLM Subgrid Structure
Gridcell
Landunits
Glacier
Wetland
Lake
Urban
Vegetated
Columns
Soil Type 1
PFTs
Keith Oleson
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CLM Subgrid Structure
Gridcell
Landunits
Glacier
Wetland
Lake
Vegetated
Urban
Industrial
Columns/PFTs
Medium Density
Suburban
Pervious
Shaded Wall
Roof
Sunlit Wall
Impervious
Canyon Floor
Keith Oleson
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Climate Science Program at UT-Austin
www.geo.utexas.edu/climate

• NOAA, Understanding and Simulation of the
  Effects of Vegetation on North American Monsoon
  Precipitation.
• NASA/NOAA, Parameterization of Snow Cover
  Fraction in Climate and Weather Prediction
  Models.
• EPA, Impacts of Climate Change and Land Cover
  Change on Biogenic Volatile Organic Compounds
  (BVOCs) Emissions in Texas.
• DHS, Regional Scale Flood Modeling for the San
  Antonio River Basin, 3-yr Graduate Fellowship to
  Marla Knebl.
• NSF, Including Aquifer into the Community Land
  Model, 3-yr Graduate Fellowship to Lindsey
  Gulden. Groundwater and Runoff
• NASA, Using MODIS Data to Characterize Climate
  Model Land Surface Processes and the Impacts of
  Land Use/Cover Change on Surface Hydrological
  Processes.

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Integrated Environmental Modeling Framework
Climate Change and Variability
Remote Sensing and GIS
Water Resources Applications
Coupled Ocean-Atmosphere Models
Air Quality
Air Quality Models
Mesoscale Models
Soil-Vegetation-Atmosphere Transfer
E
Policy
P
Qs
Hydrologic/Routing Models
D Ss
Qg
D Sg
Ig
In Situ Data
Water Quality and Quantity
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Coupling Land Surface with Other Processes
NCAR CLM Website