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Folsom Lake, California in 2012 is a visible reminder of how dependent we are on available fresh water for so many uses, from crops, to energy production, to recreation and household use. Finding and gauging the water vulnerabilities and resilience of communities around the world is an important charge for science. Photo courtesy of the U.S. Geological Survey, Department of the Interior/USGS. Enlarge Image.

Researchers at Pacific Northwest National Laboratory's Joint Global Change Research Institute (JGCRI) developed a unique modeling capability to understand how global water supplies and demands might interact over the rest of the century under different assumptions about the future. The new capability combined projections of the global water demand from all end-uses, balanced and limited by the water available at the scale of major river basins.

Results: The results suggest that long-term projections of water use that do not account for water availability and constraints are likely to overestimate the use of water and scarcity in the long-term. The analyses also show that limitations of freshwater availability in several basins altered the long-term demand and pattern of global water use, particularly for agricultural production and trade. The study highlights the importance of accounting for water as a limiting factor.

"We now have a comprehensive modeling capability that can explore the major drivers of global water use from all human activities coupled with assessments of renewable and non-renewable water supplies," said Dr. Sonny Kim, PNNL research scientist working at the JGCRI in Maryland. "It will be very valuable for understanding whether water may limit the future growth of agricultural and energy systems, and our ability to mitigate climate change."

Why It Matters: Water will be at the heart of impacts, adaptation, and vulnerability in the United States and globally over the coming decades as countries continue to develop and the climate changes. Understanding how water scarcity affects all aspects of water use is at the heart of this research. From agriculture to energy and human needs, we need to know how best to respond to and reduce the impact of regional and global water scarcity. Researchers have developed a modeling capability that provides a way to understand the impact of climate change on water availability, as well as the significance of technology improvements in response to the growing demand for water from populations and for economic growth.

The ability to fully reconcile the evolving demands for water with water resource availability uniquely places PNNL and the Global Change Assessment Model (GCAM) at the cutting-edge of investigating the interactions of regional and global water scarcity.

Methods: Researchers at PNNL expanded the GCAM, a globally integrated-assessment model, to internally balance water supplies and demands while altering irrigation patterns, bioenergy production, and electricity technologies in response to changing costs of water. (See sidebar, GCAM)

Water runoff generation simulations were based on climate scenario results from several major climate models that determined the availability of accessible renewable freshwater. Non-renewable groundwater and desalinated water contributed to the total available supply of water in the simulations. The demand for water from all human activities, including agriculture, energy, manufacturing, and municipal requirements were mapped from 14 global regions to the 235 basins.

Water demands were balanced with water supply by imposing a cost on water's use. As renewable sources of water from basins were exhausted and more expensive non-renewable groundwater and desalinated water were required to meet demand, the cost escalated. The increasing cost of water use in water-scarce regions had a notable impact on the long-term global pattern of agriculture production and trade. And, due to agriculture's greater share of water demand and sensitivity to water availability and costs, the impact to agriculture was greater than to other sectors.

What's Next? Strategies to address demand responses to increasing water scarcity and higher water costs, such as improvements to irrigation technologies, distribution efficiencies, and other adaptive measures are under investigation by JGCRI. Other ongoing activities include the explicit tracking of energy use in the water system, exploring the potential for inter-basin transfers, and better characterization of groundwater recharge and aquifers. Expansion of the GCAM water framework to sub-annual hydrologic scale is under investigation for a more comprehensive understanding of the regional and global responses to water scarcity.

Acknowledgments

Sponsors: This research was supported by the Department of Energy's Office of Science, Office of Biological and Environmental Research for the Integrated Assessment Research Program.

Research Team: Son H. Kim, Mohamad Hejazi, Lu Liu, Katherine Calvin, Leon Clarke, Jae Edmonds, Page Kyle, Pralit Patel and Marshall Wise, PNNL; Evan Davies, University of Alberta, Canada. The JGCRI is a partnership between PNNL and the University of Maryland.

Research Area: Climate and Earth Systems Science

Reference: Kim SH, M Hejazi, L Liu, K Calvin, L Clarke, J Edmonds, P Kyle, P Patel, M Wise, and E Davies. 2016. "Balancing Global Water Availability and Use at Basin Scale in an Integrated Assessment Model." Climatic Change 136:217-231. DOI: 10.1007/s10584-016-1604-6

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