Land Surface Processes in Global Climate Models (1)

1. Land Surface Processes in Global Climate Models (1)

2. Review of last lecture • Effects of different surface types: desert, city, grassland, forest, sea. Deeper heat/water reservoir, decreased Bowen ratio, thinner BL and enhanced convective instability. • Effects of vegetation: (1) makes heat/water reservoir deeper, (2) enhance evaporation, (3) grows and dies in response to environmental conditions • Heat island effect. 7 causes • Dispersion of air pollution. Dependence on stability (name of 3 types) and inversion (name of 2 types) • Global carbon cycle: linking the world together. Therefore we need to protect the environment.

3. Framework of National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM) Atmosphere (CAM) Land (CLM) Coupler . Sea Ice (CSIM) Ocean (POP)

4. Community Land Model (CLM) Design Philosophy 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.

5. CLM Model Components • Biogeophysics • Hydrologic cycle • Biogeochemistry • Dynamic vegetation

6. CLM Model Components: Biogeophysics

7. CLM Model Components: Hydrological Cycle I

8. CLM Model Components: Hydrological Cycle II

9. CLM Water balance

10. River Systems Simulated by CLM Dai, Qian, Trenberth and Milliman (2009), J. Climate

11. CLM Model Components: Biogeochemistry

12. CLM Model Components: Dynamic Vegetation

13. DGVM Vegetation biogeography vs. Satellite

14. Processes simulated in CLM3 • Vegetation composition, structure, and phenology • Absorption, reflection, and transmittance of solar radiation • Absorption and emission of longwave radiation • Momentum, sensible heat (ground and canopy), and latent heat (ground evaporation, canopy evaporation, transpiration) fluxes • Heat transfer in soil and snow including phase change • Canopy hydrology (interception, throughfall, and drip) • Snow hydrology (snow accumulation and melt, compaction, water transfer between snow layers) • Soil hydrology (surface runoff, infiltration, sub-surface drainage, redistribution of water within the column) • Stomatal physiology and photosynthesis • Lake temperatures and fluxes • Routing of runoff from rivers to ocean • Volatile organic compounds

15. Configuration of the CLM Subgrid Hierarchy The land surface is represented by 5 primary sub-grid land cover types 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.

16. Plant Functional Types

17. How processes are simulated Biogeophysical processes are simulated for each subgrid landunit, column, and PFT independently and each subgrid unit maintains its own prognostic variables. The grid-average atmospheric forcing is used to force all subgrid unit within a grid cell. The surface variables and fluxes required by the atmosphere are obtained by averaging the subgrid quantities weighted by their fractional areas.