The IMPACT model is designed to examine alternative futures for global food supply, demand, trade, prices, and food security. The IMPACT model provides both fundamental, global baseline projections of agricultural commodity supply, demand, trade, prices and malnutrition outcomes along with cutting-edge research results on quickly evolving topics such as bioenergy, climate change, changing diet/food preferences, and many other themes.
IMPACT covers 30 commodities, which account for virtually all of world food production and consumption, including all cereals, soybeans, roots and tubers, meats, milk, eggs, oils, meals, vegetables, fruits, sugar and sweeteners, and fish in a partial equilibrium framework. It is specified as a set of 115 country-level supply and demand equations where each country model is linked to the rest of the world through trade.
The model is written in the General Algebraic Modeling System (GAMS) programming language. The solution of the system of equations is achieved using the Gauss–Seidel method algorithm. This procedure minimizes the sum of net trade at the international level and seeks a world market price for a commodity that satisfies market-clearing conditions.
The basic IMPACT model is combined with the Water Simulation Model (WSM) in order to estimate the interactions between water supply and demand and food supply, demand, and trade. The scenarios for water are downscaled from and calibrated to global circulation models that represent future climates in the different IPCC SRES scenarios. This allows for separate area and yield functions for rainfed and irrigated crops, water allocation among crops, and yield and area reductions from lack of water. Water demand is accounted for from irrigation for agriculture, livestock, domestic/municipal, and industrial sectors (See Figure 2). This provides a further supply-side spatial disaggregation of production for irrigated and rainfed crop across 126 water basins. Combining these 126 basins with the 115 geopolitical regions gives 281 “food producing units,” which is an unprecedented level of detail for this type of model .
In order to explore food security effects, IMPACT projects the percentage and number of malnourished preschool children (0 to 5 years old) in developing countries as a function of average per capita calorie availability, the share of females with secondary schooling, the ratio of female to male life expectancy at birth, and the percentage of the population with access to safe water.