Hydrology in Land Surface Models

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Hydrology in Land Surface Models

• Jessie Cherry
• International Arctic Research Center Institute
  of Northern Engineering

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Many LSMs classify vegetation by biomes
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Community Land Model

• LSM for CCSM, CLM at version 3.5 (4.0 has been
  under development for 5 yrs)
• The model formalizes and quantifies concepts of
  ecological climatology
• Model components consist of biogeophysics,
  hydrologic cycle, biogeochemistry and dynamic
  vegetation
• 5 primary sub-grid land cover types (glacier,
  lake, wetland, urban, vegetated)
• The vegetated portion of a grid cell is further
  divided into patches of plant functional types,
  each with its own leaf and stem area index and
  canopy height
• Each subgrid land cover type and PFT patch is a
  separate column for energy and water calculations
• T42 2.5 deg x 2.5 deg

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CLM Model Methodology

• The model is designed to run in three different
  configurations
• 1. Stand-alone executable code as part of the
  Community Climate System Model (CCSM).
• 2. A subroutine call within the Community
  Atmosphere Model (CAM) in which CAM/CLM represent
  single executable code.
• 3. Stand-alone executable code in which the model
  is forced with atmospheric datasets. In this
  mode, the model runs on a spatial grid that can
  range from one point to global.

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Coupling Strategies
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Biogeophysics
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Hydrology and River Routing

• Includes interception of water by plant foliage
  and wood, throughfall and stemflow, infiltration,
  runoff, soil water, and snow
• Directly linked to the biogeophysics and also
  affect temperature, precipitation, and runoff
• Total runoff (surface and sub-surface drainage)
  are routed downstream to oceans using a river
  routing model only for the largest river systems

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River Routing
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Major Systems
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LSM Water Balance
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Separate River Transport Model

• A river transport model (RTM) (Branstetter et
  al., in prep) is synchronously coupled to the
  Community Land Model (CLM) for hydrological
  applications as well as for improved
  land-ocean-sea ice-atmosphere coupling in the
  Community Climate System Model (CCSM)
• This model was implemented on a 1/2 degree grid.
  Code internal to the land model interpolates the
  total runoff from the column hydrology (e.g.,
  T42, T31 grid) to the river routing 1/2 degree
  grid

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Dynamic Vegetation
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Model Component Dynamic Vegetation

• Ecosystem Carbon Balance the carbon cycle but
  also changes in community composition and
  vegetation structure in response to disturbance
  (e.g., fire, land use) and climate change
• There are two time-scales for this dynamics
  Succession considers changes in community
  composition and vegetation structure over periods
  up to several hundred years, typically following
  disturbance such as fire or land use. Over
  longer-periods of times (e.g., centuries,
  millennia) the biogeography of vegetation changes
  in response to climate change.

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Succession/Change in Biogeography
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