Hydrology in Land Surface Models

Jessie CherryInternational Arctic Research Center & Institute of Northern Engineering

Many LSMs classify vegetation by biomes

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

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.

Coupling Strategies

Biogeophysics

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

River Routing

Major Systems

LSM Water Balance

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

Dynamic Vegetation

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.

Succession/Change in Biogeography