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

www.ifpri.org 3

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

www.ifpri.org

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

www.ifpri.org

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

www.ifpri.org

IMPACT Model – Schematic

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

8

www.ifpri.org

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.

www.ifpri.org

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

www.ifpri.org

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

www.ifpri.org

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

www.ifpri.org

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

Summary of IMPACT Water

14

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

15