A Review of Continental-to-Global Sustainable Water Use Assessment

Abstract

Freshwater scarcity and unsustainable water use are some of the growing concerns in many parts of the world. Increasing water demand accompanied by increasing climate change leads to the unsustainable use of freshwater resulting in water scarcity. Several studies have quantified sustainable water use and water scarcity at a global level in the past. This review focusses on such 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 comprised of the main components of water demand and supply. Large-scale assessments have become an important tool to quantify the impacts of global climate change and water use changes on water resources sustainability. The major components comprising the water demand and the supply are estimated by such assessments using global earth system models and national level census datasets. The selection of appropriate spatial and temporal scales for the major components of water demand and supply is critical. The grid-based global earth system models enable various spatial resampling of water information over the country/political boundaries. Recent studies observed that by refining 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. In addition, the major drivers of water scarcity are discussed as an important criterion. Although both changing climate and increase in water demand contribute to the sustainability of water use, the majority of the literature concludes that the magnitude of demand driven fresh water scarcity is much greater than that by climate. Further, many studies neglect the environmental flows in large-scale assessments which results in under estimation of water scarcity.