WOLFRAM SYSTEM MODELER
Land_FertilityLand fertility |
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Diagram
Wolfram Language
In[1]:=
SystemModel["SystemDynamics.WorldDynamics.World3.Land_Fertility"]
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Information
This model computes the land fertility as a function of its utilization. Land can be overused. If that happens, the fertility of the land shrinks. This is likely to happen as the overall world population continues to climb.
The land fertility is measured in kilograms of equivalent vegetable food per hectare and year. Arable land can be used to either grow vegetable food directly, or alternatively, to raise animals that then enter the human food chain. Yet it takes more land per human to raise animals than to grow vegetable food. For this reason, it is meaningful to convert proteins obtained from eating meat to equivalent units of vegetable food.
Notice that this model uses two different types of rate models. Whereas the yield technology rate is a so-called bi-flow, i.e., it can assume both positive and negative values leading to a change of flow direction, the land fertility integrator uses uni-flows, i.e., flows that are allowed to flow in the indicated direction only.
Parameters (6)
| des_food_ratio_dfr |
Value: 2 Type: Real Description: Desired food ratio |
|---|---|
| inherent_land_fert |
Value: 600 Type: Real (kg/(hectare.yr)) Description: Inherent land fertility |
| land_fertility_init |
Value: 600 Type: Real (kg/(hectare.yr)) Description: Initial industrial investment |
| t_policy_year |
Value: 4000 Type: Real (yr) Description: Year of policy change |
| yield_tech_init |
Value: 1 Type: Real Description: Initial yield technology factor |
| p_yield_tech_chg_mlt |
Value: {0, 0, 0, 0} Type: Real[:] Description: Yield technology change multiplier |
Connectors (5)
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p_fr_inp_for_land_maint |
Type: MassInPort Description: Fraction of investments in the agricultural sector allocated to land maintenance |
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ppoll_index |
Type: MassInPort Description: Persistent pollution index |
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land_fertility |
Type: MassOutPort Description: Land fertility |
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food_ratio |
Type: MassInPort Description: Food ratio |
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yield_tech_LYTD |
Type: MassOutPort Description: Technology induced absolute yield enhancement |
Components (16)
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Source1 |
Type: Source Description: This is the (dummy) source model of System Dynamics |
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Land_Fert_Regen |
Type: RRate Description: p.328 of Dynamics of Growth in a Finite World |
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Land_Fertility |
Type: Level Description: p.324 of Dynamics of Growth in a Finite World |
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Land_Fert_Degr |
Type: RRate Description: p.326 of Dynamics of Growth in a Finite World |
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Sink1 |
Type: Sink Description: This is the (dummy) sink model of System Dynamics |
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Land_Fert_Reg |
Type: Land_Fert_Reg Description: p.328 of Dynamics of Growth in a Finite World |
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Land_Fert_Deg |
Type: Prod_2 Description: p.326 of Dynamics of Growth in a Finite World |
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Land_Fert_Regen_Time |
Type: Tabular Description: p.330 of Dynamics of Growth in a Finite World |
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Land_Fert_Degr_Rt |
Type: Tabular Description: p.326 of Dynamics of Growth in a Finite World |
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Yield_Tech_Chg_Rt_LYTDR |
Type: Rate_1 Description: Unrestricted rate element with one influencing variable |
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Yield_Tech_Chg_Rt |
Type: Yield_Tech_Chg_Rt Description: Yield technology change rate |
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P_Yield_Tech_Chg_Mlt_LYCM |
Type: Tabular Description: Tabular function |
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Add1 |
Type: Add Description: Output the sum of the two inputs |
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Des_Food_Ratio_DFR |
Type: Const Description: A constant factor |
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Source2 |
Type: Source Description: This is the (dummy) source model of System Dynamics |
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Yield_Tech_LYTD |
Type: Level1a Description: General System Dynamics level with no outflow |
Used in Examples (11)
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SystemDynamics.WorldDynamics.World3 Original WORLD3 model |
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SystemDynamics.WorldDynamics.World3 More abundant non-recoverable natural resources |
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SystemDynamics.WorldDynamics.World3 More accessible non-recoverable natural resources and pollution control |
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SystemDynamics.WorldDynamics.World3 More accessible non-recoverable natural resources, pollution control, and land yield enhancement |
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SystemDynamics.WorldDynamics.World3 More accessible non-recoverable natural resources, pollution control, land yield enhancement, and erosion protection |
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SystemDynamics.WorldDynamics.World3 More accessible non-recoverable natural resources, pollution control, land yield enhancement, erosion protection, and resource efficiency |
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SystemDynamics.WorldDynamics.World3 More abundant non-recoverable natural resources and birth control |
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SystemDynamics.WorldDynamics.World3 More abundant non-recoverable natural resources, birth control, and stable industrial output |
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SystemDynamics.WorldDynamics.World3 Combining the measures of Scenarios #6 and #8 |
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SystemDynamics.WorldDynamics.World3 Influencing the future 20 years earlier |
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SystemDynamics.WorldDynamics.World3 Influencing the future 10 years later |