Projecting bilateral virtual water trade of rice and wheat toward 2100 under different SSP scenarios

Virtual water trade (VWT) redistributes water embodied in agricultural commodities across borders and thereby shapes global interdependence between water resources and food security. Recent studies have increasingly used integrated assessment models (IAMs)—including GCAM, a partial-equilibrium IAM—to project future agricultural production and trade balances under future climate and socio-economic change and to infer virtual water transfer flows(e.g., Graham et al., 2020). However, such approaches assume that commodities are traded in a single global markets, making it difficult to explicitly quantify bilateral exporter–importer dependency structures.In this study, we develop a scenario-based framework to estimate bilateral virtual water trade of rice and wheat toward 2100 by combining projections of harvested area (land-use), climate-driven yield changes, and population dynamics with an extrapolation of current trade structures. Using baseline bilateral trade matrices from FAOSTAT, we assume that (i) exporter-specific allocation to destination countries and (ii) national export-to-production ratios remain fixed, and we scale bilateral trade volumes in accordance with scenario-driven changes in production and demand. We then compute bilateral VWT by linking projected crop flows with crop- and location-specific water-use coefficients. The analysis focuses on SSP2 as the primary scenario, with additional SSP comparison(SSP126 and SSP585). This framework enables assessment of how future VWT magnitude and bilateral dependency patterns may evolve differently between rice—characterized by relatively thin international markets—and wheat, which is traded in thicker global markets, providing insights for water–food security assessment under future climate and socio-economic change.