Water security in a warming climate

Oct 03, 2016

Californians are currently struggling with what one source has referred to as the worst drought in more than 1,200 years, and this may be only the beginning. Increases in the frequency and intensity of floods and droughts may pose potentially severe challenges to water supply throughout the southwestern United States by mid-century. That is the verdict of a new study by researchers at Loyola Marymount University (LMU) and the Climate Change Science Institute (CCSI) at Oak Ridge National Laboratory (ORNL).

Projected average daily changes in (a) surface temperature (°C), (b) January–April snow depth (mm/day), and (c) January–April albedo (%) by 2050. Projected average annual change in (d) precipitation (mm/year), (e) evapotranspiration (mm/year), and (f) runoff (mm/year) by 2050. Stippling indicates 70% or more model agreement for positive or negative changes. 

In one of the most comprehensive assessments of water supply reliability in the southwestern United States to date, the LMU-CCSI team used a high resolution (4 km) multi-ensemble hierarchical modeling framework and ORNL’s Titan supercomputer to overcome limitations in previous studies and provide a regional focus on water security. What they discovered was that a perfect storm was brewing, not only for California, but for the entire southwestern United States, which is heavily dependent on snowmelt-driven sources of water—sources particularly vulnerable to temperature change.

As reported in the study, temperature increases in the southwestern United States, which have exceeded global averages over the past century, are projected to continue. This will result in a shift of snowmelt timing that, when coupled with more extreme precipitation events, may fill reservoirs earlier in the year, requiring the release of water for flood protection purposes. The result: In the summer, when the demand for water increases, less water will likely be available, even during wet years.

In addition to flood events, the study also projects an increase in the occurrence and severity of drought conditions, or years with low annual runoff.

Projected population increases and attendant increases in demands for water will further exacerbate water security issues in the region.

“The bottom line is that by 2050, rising populations coupled with a lack of local water supply expansion could mean climate change impacts would leave the entire southwestern United States more prone to water-supply shortages,” says Brianna Pagán, one of the project leaders.

Pagán, who worked on this study at LMU and during summers at ORNL and is now a PhD student at UCLA, says the study provides new insights to water managers regarding flood and drought risks; however, there are constraints on many potential mitigation strategies that could leave the area prone to extended periods of water shortages.

To learn more about the study, study methods, and conclusions, see the recently published “Extreme Hydrological Changes in the Southwestern US Drive Reductions in Water Supply to Southern California by Mid Century,” in Environmental Research Letters.

To watch a video summary of this research, click here.

The study was funded by the LMU Rosecrans Endowment, DOE Office of Science Regional and Global Climate Modeling Program, and ORNL Laboratory Directed Research and Development funds. Support for model simulations, data storage, and analysis was provided by the Oak Ridge Leadership Computing Facility, which is supported by the DOE Office of Science.

By VJ Ewing