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Modularity in Inter-Disciplinary Model Systems: Examples from
the IFPRI IMPACT Model Sherman Robinson
International Food Policy Research Institute (IFPRI) September 2014
www.ifpri.org
Drivers of Agricultural Growth and Food Security
Demand drivers • Population growth: 9 billion people in 2050
• Urbanization: 50% in 2008, 78% in 2050
• Income growth
• Oil prices
• Biofuels and bioenergy
• Conservation and biodiversity
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Rapid income growth and urbanization – effects on diets and patterns of agricultural production • Increased consumption of fruits and vegetables • Rapid growth in meat consumption and demand for grains
for feed • Change in diets to convenience foods, fast foods • Higher food energy, more sugar, fats and oils • Half of growth in grain demand will be for
Livestock feed • Increased pressure on land and water
Drivers of Agricultural Growth and Food Security
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Supply drivers • Climate change
• Water and land scarcity
• Investment in infrastructure
• Investment in agricultural research
• Policy
http://media.npr.org/assets/img/2012/07/18/drought18-
8b9a6db718dda8f9f968da97316f9c0a2daa3655-s40-c85.jpg
Drivers of Agricultural Growth and Food Security
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The IMPACT Model
International Model for Policy Analysis of Agricultural Commodities and Trade Need for a multi-disciplinary approach, e.g.
• CGIAR Centers: Economics, agronomy, hydrology, livestock, fish, crop models, etc.
• Civil engineering: infrastructure • Climate change (GCMs) • Energy
Water models • Hydrology • Water Basin Management • Water Stress on economy
Sugar and oilseeds • Processing activities
Livestock/meat/dairy Fishery
Multimarket model • Crop production, demand,
international trade
SPAM: Spatial Production Allocation Model Land-Use DSSAT Crop Models Biofuels
IMPACT Suite of Models 7
IMPACT version 3
159 • Countries
154 • Water
Basins
320 • Food
Production Units
• 58 Agricultural commodities
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Desiderata for Modular Model Systems
A “module” should be designed to: Read its own parameters; Initialize its own variables; Accept variables passed to it from other modules and
the environment; Pass variables that are computed within the module to
other modules or the main model; Own its set of state variables; Operate in “standalone” mode.
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Modules in the IMPACT Model System
Water models: hydrology, water basin management, crop stress Crop models: DSSAT, etc. Land use models (including SPAM) Livestock models, including fisheries Crop processing: sugar, oil seeds, cassava Biofuels
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Modularity: Linking Modules
Modularity = “a la carte” model system • Use the models you need, turn off those you do not need • Separate models can be run independently • Modules can run on different time steps
Standardize data transfer • Information Flows • Dynamic or Iterative interaction
“Data driven” model specification • IMPACT model can be run at any level of aggregation
without changing the model code • Change input data and sets only: user need not even see
the GAMS code
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Modularity: Linking Modules
Three ways to link modules: • Exogenous: Information flows in one direction
– Hydrology, DSSAT, GCMs, SPAM • Linked dynamically: Two-way information flow between years
– Water basin management, water stress on crops – Land use
• Endogenous: Module equations are solved simultaneously – Livestock, sugar processing, oilseeds/oils – Land allocation to crops
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Water Models in IMPACT
Global hydrological module (GHM) assesses water availability
IMPACT Water Simulation Module (IWSM) optimizes water supply according to demands • Monthly time step • Domestic, industrial (linked to GDP/population) • Livestock • Environment • Irrigation
Water stress module • Delivers crop yields to the IMPACT food module
Water: Two-Way Model Integration
Food Model • Crop Areas • Population • GDP • Livestock
Numbers • Prices
Water Model • Water Stress
Shock on Crop Yields
Solve Food Model in Stand Alone Mode
Fix Areas and Livestock Numbers and call the Water
Model
Resolve the Food Model using Fixed
Areas and Livestock with new yields including Water
Stress
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