We may not, as the old saw goes, be able to do anything about the weather. But research is providing the tools to show us what nature has in store so that we can better manage our water supplies, mitigate floods and protect our ecosystem.
In California, currently suffering its historic drought, managing the water supply is a critical concern. According to a recent NASA report, it will take 11 trillion gallons of water to replenish the state's diminishing reservoirs. And for the first time in history, the governor has issued a statewide water-reduction mandate.
"The climate is changing," said F. Martin Ralph, director of the new UC San Diego-based Scripps Institution of Oceanography Center for Western Weather and Water Extremes, known as CW3E. "Some of that is natural, some is anthropogenic. But whatever its cause, we are working on tools that can improve our ability to adapt to this change and that can help mitigate emissions."
Ralph has collaborated with other UC San Diego researchers and with federal, state and local agency partners. Their findings are currently being applied in the CalWater experiment, which aims to improve the accuracy of long-term climate projections over decades, as well as the accuracy of short-term weather forecasts.
Atmospheric rivers and aerosols
One key to that improved accuracy grew out of Ralph's investigation of atmospheric rivers, huge streams of water vapor that swiftly travel long distances through the earth's atmosphere. What he and colleagues discovered was that in any given year, atmospheric rivers cause between 25% and 50% of all precipitation in northern California and the West Coast.
This finding has been useful not only in the CalWater project but also in weather forecasting. Anyone can access atmospheric river information on the CW3E website (cw3e.ucsd.edu).
"The atmospheric rivers bring the water vapor to California," Ralph said. Clouds then form when that water vapor condenses on a variety of particles in the air known as aerosols, which are being studied in detail by other scientists at UC San Diego. The type and abundance of aerosols in those clouds determine whether they'll bring rain or snow — or no precipitation at all.
As our understanding of atmospheric rivers and aerosols leads to more accurate weather predictions, we could create new reservoir management options that'll play a crucial role in adapting to climate change, Ralph said. If we improve our ability to predict heavy storms brought by atmospheric rivers, then it may be possible to save extra water that would normally be released after a storm — or released before a major storm that could bring flooding.
Operating reservoirs in a different way
What will happen when this strategy is put to the test?
"It's a very challenging task to change reservoir operations in a way that does not increase flood risk or worsen water supply problems and at the same time does not cause problems for endangered species such as salmon," Ralph said.
That's why CW3E has joined forces with the Sonoma County Water Agency in a study called FIRO, or forecast-informed reservoir operation. Drawing on experts from science, government and the Army Corps of Engineers, FIRO is working on assessing Lake Mendocino in Northern California, which, for a variety of reasons, has had chronically low water levels.
One of the project's goals is to analyze the role of atmospheric rivers in filling Lake Mendocino and to offer solutions that will help retain water without increasing flood risk. If FIRO can improve conditions at Lake Mendocino, the knowledge gained might work for other reservoirs across the state and possibly across the entire American West.
"The potential for these new findings is very motivating," Ralph said. "We know now about some key things to implement, and about what new directions to pursue in science, technology and engineering to ensure the best tools are available for future water management."