Hydrology in Land Surface Models Jessie Cherry International Arctic Research Center & Institute of Northern Engineering
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.
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
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
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.