SIMPLE is a partial equilibrium agricultural trade model that has been validated for the study of the long-run sustainability of the global food system. SIMPLE-G extends the SIMPLE model to include gridded biophysical and economic relationships pertinent to the land-water-energy nexus. This model is multi-scale simultaneously solving for outcomes at the level of individual grid cells, while also resolving regional and global market equilibria. This allows SIMPLE-G to explicitly incorporate local heterogeneity in climate, soils, water, and regulatory institutions while also capturing global change drivers and feedbacks for local adaptations to national and international markets. At each grid cell, competition for land and water resources ensures a linkage to environmental and natural ecosystems. We model economically motivated changes in land use as well as changes in water withdrawals which reflect differential resource availability and constraints. The model solves for equilibrium quantities and prices for land and nonland inputs as well as for irrigation water, and crop outputs. Equilibrium water withdrawals and energy requirements are endogenously determined at each grid cell assuming a grid cell-specific shadow price for water within the grid cell. Crop prices are permitted to vary by region based on the extent of domestic market segmentation from the world market.
While there are other models that use a grid-resolving approach to a global economic analysis of sustainability challenges, SIMPLE-G is the first that is fully open-source and available to run in the clouds. It is designed to be readily adapted by other researchers working at the interface of the land-water-energy nexus. The outcomes of the model provide quantitative insights about global-to-local connections (e.g. the importance of growth in income and population outside the US as drivers of US crop production) and local-to-global linkages (e.g. while the aggregate impact of the water withdrawal restriction on US crop production and land use is small, it has a significant impact on the pattern of crop production and cropland area, both in the US and overseas).
We introduce SIMPLE-G, a Simplified International Model of agricultural Prices, Land Use, and the Environment- Gridded version, as a novel tool for evaluating sustainability policies in a global context while factoring in local heterogeneity in land and water resources and natural ecosystem services. This multi-scale model can provide boundary conditions for local decision-makers, as well as capturing feedback from local policies to national and global scales. To illustrate its value in environmental analysis, we provide two applications of the model. First, we quantify the local stresses on land and water resources due to global changes in population, income, and productivity. Second, we quantify the global impacts of local policy responses and adaptations to water scarcity.