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IFPRI IMPACT 3 Model System:Modularity
Sherman RobinsonIMPACT Model Team
International Food Policy Research Institute (IFPRI)Rome, GFSF Team Meeting, May 2015
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The IMPACT 3 Model
International Model for Policy Analysis of Agricultural Commodities and Trade
Need for a multi-disciplinary approach:• CGIAR and other collaborators:
– Economics, agronomy, hydrology, livestock, fish, crop models, nutrition/health
• Civil engineering: infrastructure• Climate change (GCMs)• Energy (biofuels, inputs)
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IMPACT version 3
159
• Countries
154
• Water Basins
320
• Food Production Units
• 58 Agricultural commodities
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IMPACT 3.2: A Suite of Models
Multimarket model• Core global PE model
SPAM:• Spatial Production
Allocation Model
Land-Use DSSAT Crop Models Welfare
Water models• Hydrology• Water Basin Management• Water Stress on yields
Sugar and oilseeds• Processing value chains
Livestock/meat/dairy• Current version running
Nutrition/health: • Current version running
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IMPACT 3.2 to 3.3: Improvements
Data on policies: tariffs and subsidies (GTAP data, OECD PSE/CSE data• Incorporated into IMPACT 3.2 data set
Review of productivity growth trends and model improvements by CGIAR centers• Rome GFSF meeting, May, 2015
Menu of possible model improvements• Priority setting
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IMPACT 3.3: Potential Improvements
Livestock module: under development with ILRI Fish module: joint work with World Fish
• Two stage work program underway Linked global CGE model: joint work with IDS Links to environmental models
• Biodiversity: IFPRI and Bioversity• GHG emissions, nitrogen use efficiency: IFPRI
Water model improvements:• Ground water • Water quality
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IMPACT 3.3: Potential Improvements
Micronutrient module: IFPRI, PHND, A4NH and others• Under development
Health module: with Oxford (Martin Centre)• Under development
Land module: land supply and demand by type• Under development at IFPRI
Variability and extreme events• Work with UK/US collaborators (sponsored by Lloyds)
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Nutrition Module
IMPACT model solves for supply/demand for agricultural commodities in physical units• Nutrition module: post solution calculation of nutrition impacts
Nutrition content measured at the agricultural commodity level--extensive empirical work• FAO: Food balance sheets. Nutrition content of various
agricultural commodities, focusing on “energy” (calories)• IFPRI (PHND, Haddad-Smith, Derek Headey), CSIRO (Mario
Herrero), CIMSANS (Jerry Nelson), Oxford (Marco Springmann), Nestle Research– Extending food balance sheets to include more nutrients
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Nutrition Module: Regression Model
Reduced-form regression models• Statistical models linking nutrient supply at the commodity level
to nutritional status at the household/ consumer level• Haddad/Smith cross-country regression model is currently used
in IMPACT to calculate nutrition outcomes, focusing on energy– Nutrient supply is one variable among many in the model,
but is the only variable linked to IMPACT– They are updating the regression model to include more
nutrients and outcomes (obesity as well as under nourished)
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Nutrition Outcomes
Since actual household demand is for processed commodities (e.g., bread, not wheat), food balance sheets measure supply of nutrients, not what is actually consumed at the household level• Haddad-Smith regression model skips value chain to processed
food commodities • Nestle: EcodEx (Product Ecodesign Tool) considers value chains
to processed commodities and 32 nutrients• Tilman et al.0(2011), “Global food demand and the sustainable
intensification of agriculture”– Demand functions for “nutrients”
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Nutrition:
• Oxford Martin Programme on the Future of Food, study linking IMPACT model results for fruit and vegetable and red-meat consumption on body weight and health outcomes using a Markov model and detailed information on nutritional content of foods– Springmann et al. paper– Health outcomes linked more to consumption of fruits and
vegetables (micronutrients) than to energy (calories)
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Production to Nutrition
To support more structural models of food demand and nutritional status requires specifying the value chain in both PE and CGE models• Wheat to flour to bread/pasta/cake to retail sector to
households • Production of “other” food commodities such as beverages, fish
products, etc. Extensive data on nutritional content of processed food
commodities. • Feasible to use these data in models?
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Demand, Utility, and Nutrition
How to link nutritional status and commodity demand functions:• Current practice. Add equations determining nutritional status
as an “add on” after commodity demands have been determined based– Data are available, both at the agricultural and food
commodity levels. Current treatment is to work at the agricultural commodity level.
– Thin links with utility/demand theory. Households demand food commodities, not agricultural products or nutrients. Only an indirect link with nutritional status indicators.
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Demand, Utility, and Nutrition
Add nutrition indicators to the utility function, with implications of commodity demand• Hedonic quantity/price indices: consumers do not demand
nutrients, but commodities with nutritional attributes– K. Lancaster, “A New Approach to Consumer Theory”, 1966
Add nutritional status indicators as constraints in the utility optimization problem• Integrate the classic LP “diet problem” with an NLP utility
maximization problem
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IMPACT 3.4: Potential New Modules
Production: better specification of technology and supply• Optimization given production/cost functions (CGE models)• Activity/process specification of production/costs
– GLOBIOM (IIASA), MAgPIE (PIK, Potsdam)• Stylized “farm” simulation models
Value chains: more “processing” activities to move from crops/livestock to marketed “commodities”• From cows to hamburgers & milk (livestock module) • From wheat and corn to Wheaties and Cornflakes• Cassava: food vs industrial demand, tradability
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Current Value Chain Modules
Oilseeds and sugar (integrated in IMPACT)• Processing from crops (sugar cane/beet, various oil seeds) to
“commodities”: processed sugar, oils, meal• Simple cost pricing: “markup” on cost of crop inputs• Implicit assumption of competitive markets
Livestock (standalone module and integrated)• Value chain from herds to dressed meat, eggs, milk• New livestock module: elaborate specification of feed inputs
and livestock production “systems”• Simple model of commodity production: “markup” on inputs• Implicit assumption of competitive markets
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New Value Chain Modules
Interest in expanding range of value chain modules• Cassava, fish, wheat/maize/rice/soy beans• Welfare analysis using demand curves for intermediate inputs is
problematic—consumer surplus calculation is suspect• Links to nutrition analysis: more detail on food commodities• Simple specification of competitive markets is suspect
– E.g., sugar Combine value chain with industry studies
• “Structure, conduct, performance” analysis• Schmalensee and Willig: Handbook of Industiral Organization
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Linked Global CGE Model
New project: link IMPACT 3 with the GLOBE CGE model• GLOBE is based on GTAP data and written in GAMS• Includes activity/commodity distinction, as in IMPACT 3
One-way links: IMPACT to GLOBE• Crop/livestock production from IMPACT 3 passed to GLOBE,
which then is run assuming those outputs are fixed• GLOBE solves for economywide impacts (direct and indirect
links): production, employment, and prices• All welfare analysis is done in GLOBE (EV/CV, total absorption)• Links to labor markets, wages, and poverty done in GLOBE
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Linked Global CGE Model
Two-way links: IMPACT to/from GLOBE• Agricultural output from IMPACT: GLOBE generates GDP
originating in agriculture, and changes in total GDP• GDP from GLOBE sent back to IMPACT, so GDP in IMPACT
reflects changes in agricultural productivity– Currently, GDP is exogenous in IMPACT
GLOBE and IMPACT need not run on the same time step• Both can be annual, but can run on different multiyear time
steps (e.g., annual for IMPACT, every 5 years for GLOBE) GLOBE linked via a standalone module that takes input
from IMPACT and runs GLOBE
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Advantages of Modularity
“Standalone” modules can be run independently of IMPACT, but use inputs from IMPACT scenarios• Can be developed, calibrated, and tested by specialists (e.g,
from various CGIAR centers). • Designed to be used in Center research programs
Design: separate modules can reflect their disciplines• No need to compromise to “fit” one model into another• E.g. water in economic models or economics in water models—
always unsatisfactory Model development, testing, and debugging is greatly
facilitated if the modules can be run separately
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Desiderata for Modular Model Systems
“Modules” should be designed to: Operate in “standalone” mode; Read its own parameters; Initialize its own variables; Accept variables/parameters 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;
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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 with different time steps
Standardize data transfer• Information flows• Dynamic or iterative interaction
“Data driven” model specification• IMPACT 3 multimarket 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
– To IMPACT: hydrology, DSSAT, GCMs, SPAM– From IMPACT: welfare, nutrition/health, GLOBE/CGE
• Linked dynamically: Two-way information flow between years– Water basin management, water stress on crops– Land use by type– GDP/economywide links: GLOBE
• Endogenous: Module equations are solved simultaneously– Livestock, sugar processing, oilseeds/oils– Land allocation to crops
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IMPACT 3 Modules
Standalone modules, one-way links:• Welfare, nutrition, GLOBE (e.g., welfare, economywide impacts),
hydrology, DSSAT, GCMs
Standalone modules, inter-period links:• Water models (IWSM, water stress), land use (by land type),
livestock (herds), GLOBE (e.g., GDP, non-ag prices)
Standalone modules, intra-period links:• Land use (cropping, irrigated/rainfed), Livestock
Value chains, within IMPACT: sugar, oilseeds, livestock
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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, environmental, and irrigation demands• Optimizing model for irrigation demand/supply
Water stress module • Optimizing model: allocation of water to crops• Deliver crop yields to the IMPACT multimarket model
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Water: Two-Way Model Integration
Food Model• Crop areas• Population• GDP• Livestock
numbers• Prices
Water Models• Water supply• Water Stress:
shock on crop yields
Solve multimarket model given trends
and variable crop areas
Fix crop areas and
livestock; call
the water
models: solve
for water stress yields
Re-solve the
multimarket
model with fixed crop
areas and
stress yields
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In each year, solve in two steps:
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Standalone IMPACT Module: Template GAMS IMPACT-compatible standalone module
• Include file with definition of relevant IMPACT parameters• Include GDX file(s) of scenario output of IMPACT results• Load IMPACT data needed by the module
Data estimation and management• Module has its own data base, in addition to IMPACT data
Model specification and parameterization• If module is to be integrated with IMPACT, must avoid name
collisions for parameters, variables, and equations Linking to IMPACT 3
• Communication: exogenous, intra-period, within-period
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