Human activities are increasingly leading to overuse of surface water and nonrenewable groundwater, challenging the capacity of water resources to ensure food security and continuous growth of the economy. Adaptation policies targeting specifically water security can easily overlook its interaction with other sustainability metrics and unanticipated local responses to the larger-scale policy interventions. Using a recently developed global partial equilibrium, grid-resolving model, nick-named SIMPLE-on-a-Grid and coupling it with the global Water Balance Model, we simulate the impacts of reducing unsustainable irrigation water withdrawals on land use change and food supply, under a variety of future (2050) scenarios with and without adaptations. Comparisons are made among three policy interventions: inter-basin water transfers, investments in agricultural productivity-enhancing technologies, and the promotion of virtual water trade. Although each of these scenarios affects regional food supply in a similar fashion, their implications for land cover change, carbon emissions and global food security are quite different. By allowing for a systematic comparison of these alternative adaptations to future scarcity, the global gridded modeling approach offers unique insights into the multiscale nature of the water scarcity challenge.