The Simple Biosphere Model Version 4.2: SiB4 Technical Description Katherine Haynes, Ian Baker, Scott Denning Colorado State University Fort Collins, Colorado February 2020 Contents List of Figures iv List of Tables v 1 Introduction 1 1.1 Overview . .1 1.2 History . .2 1.3 Applications . .8 2 Model Structure 10 2.1 Soil and Snow . 10 2.1.1 Structure . 10 2.1.2 Soil Properties . 11 2.2 Vegetation . 12 2.2.1 Plant Functional Types . 12 2.2.2 Root Profiles . 13 2.2.3 Carbon Pools . 14 2.2.4 Vegetation Properties . 15 2.2.5 Land Cover Heterogeneity . 16 2.3 Input Variables . 16 2.4 Prognostic Variables and Governing Equations . 18 2.5 I/O . 21 2.6 Runtime Options . 23 3 Radiation 26 3.1 Solar Radiation Characteristics . 26 3.2 Solar Radiation Components . 27 3.3 Radiative Transfer Model . 28 3.3.1 Overview . 28 3.3.2 Original Equations . 28 3.4 Radiation Calculations . 29 3.4.1 Albedo . 29 3.4.2 Radiation Absorption Factors . 30 3.4.3 Absorbed Radiation . 30 3.4.4 Net Radiation . 31 i 4 Land-Atmosphere Exchanges 32 4.1 Aerodynamic Resistances . 32 4.2 Photosynthesis . 34 4.2.1 Assimilation . 34 4.2.2 Stomatal Conductance . 36 4.2.3 Canopy Scaling . 36 4.2.4 Environmental Forcing Potentials . 37 4.3 Fluxes . 38 4.4 Energy Balance . 39 5 Hydrology 41 5.1 Precipitation . 41 5.2 Canopy . 42 5.3 Snow . 42 5.4 Soil . 43 5.5 Water Balance . 43 5.6 Water Availability . 44 6 Solar-Induced Fluorescence (SIF) 46 7 Carbonyl Sulfide (COS) 48 7.1 Leaf Uptake . 48 7.2 Soil Uptake . 49 7.3 Prognostic Canopy Air Space (CAS) COS . 50 8 Dynamic Prognostic Phenology 51 8.1 Phenology Stages . 52 8.2 Stage Selection . 53 8.2.1 Phenology Index (PI ).......................... 53 8.2.2 Day Length Potential (PSDayL)..................... 53 8.2.3 Growth Potential (PSGrw)........................ 55 8.2.4 Weather Potential (PSWx)........................ 57 8.3 Growing Season Start . 58 8.4 Phenology and Physiology Interactions . 59 9 Defined Prognostic Phenology (Crops) 61 9.1 Phenology Stages . 62 9.2 Growing Season Start . 63 9.3 Seasonal Progression . 63 ii 9.4 Harvest . 64 9.5 Redistribution . 64 9.6 Switching Corn and Soybeans . 64 10 Disturbance 65 10.1 Fire . 65 10.2 Grazing . 66 11 Carbon Pool Exchanges 67 11.1 Allocation . 67 11.2 Autotrophic Respiration . 69 11.2.1 Growth Respiration . 70 11.2.2 Maintenance Respiration . 70 11.2.3 Canopy Maintenance Respiration Scaling Coefficient . 71 11.2.4 Root Maintenance Respiration Scaling Coefficient . 73 11.2.5 Diagnostic Respiration Rates . 74 11.3 Senescence . 75 11.3.1 Turnover . 75 11.3.2 Litterfall . 75 11.3.3 Transfer . 77 11.4 Heterotrophic Respiration and Decay . 77 11.5 Pool Updates . 80 12 Terrestrial Carbon Cycle 81 12.1 Overview . 81 12.2 Calculation Sequence . 82 References 83 Acknowledgements 100 Appendix A: Input Data and Parameters 101 Appendix B: Variables 114 iii List of Figures 1.1 Framework of the Simple Biosphere Model (SiB) (Sellers et al., 1986). .2 1.2 SiB2 (Sellers et al., 1996a). .3 1.3 SiB3. .4 1.4 SiB4 (Haynes et al., 2019a). .7 1.5 Future Applications. .9 2.1 PFT Tiles. 16 2.2 SiB4 Input and Output. 21 4.1 SiB Turbulent Transfer Regimes (Sellers et al., 1996a). 33 4.2 SiB Photosynthesis-Conductance Model (Sellers et al., 1996a). 35 4.3 Example Environmental Potentials. 38 5.1 SiB Precipitation Relationships (Sellers et al., 1996a). 41 5.2 Example 3-Layer Snow Pack (Lawrence et al., 2018). 43 7.1 COS Uptake-Resistance Model (Berry et al., 2013). 48 8.1 SiB4 Dynamic (Non-Crop) Phenology. 51 8.2 Sample Day Length Potentials. 54 8.3 Example Growth Potentials. 56 8.4 Example Climate Suitability and Water Availability Relationships. 57 9.1 SiB4 Defined (Crop) Phenology. 61 11.1 Sample Canopy Assimilation Scalars for Autotrophic Respiration. 71 11.2 Sample Canopy Freeze Inhibition Scalars (MCRFreeze). 72 11.3 Sample Canopy High Temperature Scalars (MCRHot). 73 11.4 Sample Litterfall Transfer Fractions. 76 11.5 Sample Moisture Inhibitions for Heterotrophic Respiration. 79 12.1 SiB4 Carbon Cycle. 81 iv List of Tables 2.1 Soil Layer Information. 11 2.2 Plant Functional Types (PFTs). 13 2.3 Sample Root Profiles. 14 2.4 Carbon Pools. 14 4.1 Fluxes, Potential Differences, and Resistances. 38 8.1 Dynamic Phenology Stages. 52 A1 Meteorological Drivers. 101 A2 Fire Emissions. 101 A3 Structural Properties. 101 A4 Aerodynamic Parameters. 101 A5 Physiological Parameters. 102 A6 Dynamic.