Evaluating Sustainability of Projected Water Demands Under Future Climate Change Scenarios

Document Type


Publication Date



Tetra Tech for Natural Resources Defense Council


Climate change will impact water supplies, exacerbating existing pressures on water resources caused by population and economic growth. Given the combination of these stressors, the sustainability of water resources in future decades is a concern in many parts of the world. This study presents an integration of water withdrawal projections and future estimates of renewable water supply across the United States to assess future water availability in the face of a changing climate. The water demand projections in this work are based on business-asusual trends in growth, particularly of population and energy demand, and renewable water supply projections are based on the average results of an ensemble of sixteen established climate models. The analysis is performed using annual water use data at the U.S. county level, and using global climate model outputs for temperature and precipitation, both projected 20-40 years into the future. The analysis provides a national-scale evaluation of the results of changing water demand and supply, and helps identify regions that are most susceptible to climate change. As part of this analysis, a water supply sustainiability index comprised of five attributes of water use and growth was developed, and used to compare impacts across regions. We found that, under the business-as-usual scenario of demand growth, water supplies in 70% of counties in the U.S. may be at risk to climate change, and approximately onethird of counties may be at high or extreme risk. The geographic extent of potential risk to water supplies is greatly increased when climate change is considered (Figure ES‑1). This calculation indicates the increase in risk that affected counties face that water demand will outstrip supplies, if no other remedial actions are taken. To be clear, it is not intended as a prediction that water shortages will occur, but rather where they are more likely to occur. As a result, the pressure on public officials and water users to creatively manage demand and supply—through greater efficiency and realignment among competing uses, and by water recycling and creation of new supplies through treatment—will be greatest in these regions. In addition to developing national-scale maps of potential climate impacts, this work serves as a starting point for more detailed analysis, either at more local scales, or by consideration of specific sectors of the economy that are directly dependent on sustainable water resources.