A review of the assessment of sustainable water use at continental-to-global scale

Freshwater scarcity and unsustainable water use are just some of the growing concerns in many parts of the world. Increasing water demand accompanied by a changing climate can lead to unsustainable use of freshwater resulting in water scarcity. Several studies have quantified sustainable water use and water scarcity at a continental-to-global scale in the past. This review focuses on the large-scale water resources assessments and the methods by which sustainable water use and water scarcity are quantified. The review is structured based on a framework that comprises the main components of water demand and supply and other aspects of sustainable water use including virtual water trade and future projections of sustainable water use. The major components of water demand and supply in such assessments are increasingly derived from global earth system models and national-level census datasets. These assessments conclude that the selection of appropriate spatial and temporal scales is critical. The grid-based global earth system models enable better spatial resampling of water information across country/political boundaries. Similarly, by refining the temporal scale from annual (the most commonly used temporal scale of assessment) to monthly time steps, water scarcity is better captured due to the distinctive seasonality of water availability and demand. This paper also discusses the role of major drivers of water scarcity. Although both changing climate and increasing water demand contribute to water scarcity, the majority of the literature concludes that the demand-driven freshwater scarcity has a much greater impact than that induced by climate change.