Between Christmas and mid-January this yr, a parade of nine atmospheric rivers — vast streams of water vapor flowing east from the tropical Pacific — pummeled California. The trillions of gallons of rain poured on the state caused widespread flooding. While the rain topped up some drought-depleted reservoirs and aquifers and filled out snowpack within the Sierra Nevada, much of the water quickly ran off into the ocean, flowing off asphalt and farms or released from reservoirs to forestall further flooding.
For Patrick Sing, a water manager with the U.S. Army Corps of Engineers, the deluge was a chance to try something that will be dangerous anywhere else within the country.
Sing sits on the controls of Lake Mendocino, a reservoir on the Russian River near Ukiah, in northern California. Like reservoirs across the state, Lake Mendocino has seen years of maximum swings between wet and dry — it almost emptied after a dry stretch in 2021 and was near empty when the primary atmospheric river set free on December 26. Sing watched because the reservoir filled up, first topping off the zone reserved for water supply, then quickly rising into the flood zone.
In February, a month after the rains stopped falling, the reservoir was still within the flood zone, holding 11,000 acre-feet greater than the same old limit, in keeping with Sing. Normally, this water would have been released to forestall a flood within the event one other storm got here along. If more water got here too quickly, there may not be time to soundly release the additional water from the dam, risking an uncontrolled release or overtopping. But there was a dry forecast, so Sing retained the additional water. It could possibly be some time before a lot of it got here again.
For a thirsty West, forecasts could reduce flood risk in wet years and increase water supply in dry years.
Lake Mendocino is the primary and, as yet, only reservoir within the country authorized to make use of weather forecasts in making decisions about when to maintain and when to release water. The thought is that when a forecast is dry, an operator can safely keep more water in a reservoir. When the forecast is wet, they’ll cut into stores normally reserved for water supply to create space for the approaching rain. “It’s all concerning the timing, and forecasts provide you with time,” says Cary Talbot, a researcher on the Army Engineer Research and Development Center.
For thirsty farms and cities within the West, the approach could reduce flood risk during wet years and increase water supply for dry years. Lake Mendocino increased the water it stored by nearly 20 percent in its first two years. A retrospective study of the reservoir’s operations between 1985 and 2021 found water storage would have been 33 percent higher on average at the tip of the flood season if forecasts had been in use.
Researchers working on the approach within the U.S. say they aren’t aware of any similar projects in other countries, but studies suggest that integrating forecasts has the potential to enhance reservoir operations anywhere weather predictions are sufficiently reliable. The approach could also help aging dams reply to more variable precipitation seen with climate change.
Along with their work at Lake Mendocino, the Army Corps of Engineers, together with researchers on the Scripps Institution of Oceanography and other partners, are studying the approach at 4 other reservoirs inside their jurisdiction in California and Washington, including Lake Oroville, which is held back by the country’s tallest dam. These projects will support a process starting this yr to think about using weather forecasts at greater than 700 other dams the Army Corps operates across the USA, a couple of of that are among the many nation’s largest.
Those dams represent a fraction of the greater than 90,000 dams within the U.S., and the approach won’t work in any respect of them. Precipitation forecasts is probably not reliable enough within the Midwest or Gulf Coast to make decisions about water use. And lots of reservoirs aren’t built to regulate the discharge of water or may not have the resources to constantly monitor the weather and respond.
However the approach could help the country’s aging water infrastructure deal with climate change, particularly within the West, which is facing increasingly frequent and severe droughts. “We’re poising ourselves to be way more adaptive going forward,” says Talbot. “That is the following generation of water management.”
The change in considering is basically enabled by improvements in weather forecasting. “A long time ago, when the dams were built, forecasts were lousy,” says Marty Ralph, a climate scientist at Scripps, where he directs the Center for Western Weather and Water Extremes. Precipitation forecasts particularly were notoriously tricky to get right. Without reliable forecasts, dams operated by the Corps were required by law to be managed only using data on streamflow, snowpack, and actual precipitation — water on the bottom. The caution was justified, says Talbot. “Dams are dangerous. They’ve the potential to kill people and cause tremendous damage.”
In 2019 and 2020, Lake Mendocino stored 19 percent more water than it could have without using forecasts.
For the reason that Nineteen Sixties, nevertheless, weather forecasting has turn into way more reliable, driven by advances in numerical modeling, satellite data, radar, and computing power. By the late 2000s, “it was clear to me there was real potential for forecasts to be useful in reservoir operations,” says Ralph. He saw the potential on the West Coast particularly, where atmospheric rivers meeting the mountains predictably drive precipitation. “Atmospheric rivers are the forms of storms that matter for floods and for annual water supply,” he says.
Ralph proposed to collaborate with the Army Corps of Engineers on what he termed “forecast informed reservoir operations,” or “FIRO.” The project would involve research to enhance forecasts of atmospheric rivers after which using those improved forecasts to alter how California reservoirs are operated. He says the Corps was interested by the thought, however it was slow to catch on. Then, between 2012 and 2015 California endured one among its worst droughts on record, which drew attention to the state’s depleted water supply in addition to the rigid water control manuals still used at many reservoirs.
At Lake Mendocino, a wet 2012 winter saw three atmospheric rivers fill the reservoir above flood levels. As required by the reservoir’s control manual, operators released the extra water in case one other storm got here through, but no more big rains got here that yr or the following. “The reservoir never rebounded,” says Ralph. The Corps was “pretty much criticized” by politicians for counting on out-of-date manuals, says Sean Smith, the principal hydrologic engineer on the Corps. “Reservoir operations ought to be based on modern science and weather forecasts, not antiquated rulebooks,” Congressman Jared Huffman said on the time.
In 2016, Congress modified the law to offer the Army Corps permission to think about weather forecasts on the reservoirs it manages. But before forecasts could safely be used, individual dams would need to be studied to ensure the approach was protected and that weather forecasts were reliable enough in that area.
Lake Mendocino was the primary to be studied. Detailed analyses of the weather forecasts and hydrology there found that a reliable forecast five days out would give operators enough time ahead of a heavy storm to release any additional water and for that water to make it past flood-prone areas downstream. Lake Mendocino start testing the strategy. In 2019 and 2020, the reservoir stored 19 percent more water than it could have without using forecasts, enough to produce around 30,000 households for a yr.
The successful test at Lake Mendocino led to the opposite 4 projects at reservoirs in California and Washington, which can test using forecasts in areas more affected by snowmelt, with more complex systems of reservoirs, or with greater flood risk downstream.
Prado Dam on the Santa Ana River just outside Orange County will serve to check the approach in a more urban context with high flood risks. An initial assessment showed the approach is viable on the dam and would increase water supply by 7,000 acre-feet a yr without increasing flood risk. The additional water would go to recharge the groundwater that gives much of the county’s water supply. Water officials say they plan to begin using forecasts on the reservoir by October this yr.
The usage of forecasts could help the U.S. deal with drought without constructing latest water infrastructure.
Tests at Lake Oroville and Recent Bullards Bar Reservoir on the Yuba and Feather River watersheds in California’s Central Valley will gauge how forecasting will be used where snowmelt runoff is a serious variable. Also they are much larger than the opposite tests: Lake Oroville can store greater than 3.5 million acre-feet of water, while Recent Bullard’s Bar can store slightly below 1,000,000 acre-feet. By comparison, Lake Mendocino has a capability of just around 100,000 acre-feet. An initial assessment found using forecasts at the side of other changes to the dams’ spillways would cut back flood risk without impacting water supply.
The fourth test at Howard A. Hanson Dam on the Green River in Washington will test the approach in a really wet system. Forecasting could reduce flood risk and in addition help spawning salmon by allowing for greater control of water conditions, says Ralph.
Those tests will inform a screening process starting this yr to find out where else forecasts could improve operations. An initial study shows many of the dams within the Army Corp’s South Pacific Division — which incorporates California and many of the U.S. Southwest — could possibly be viable, in keeping with Smith. Elsewhere, the calculus is more complicated. “You might have to take each project in each basin one after the other,” Smith says.
Recent England, also affected by atmospheric rivers and with mountainous landscapes, has quite reliable forecasts, says Ralph, but precipitation is tougher to predict in the course of the country, where thunderstorms predominate and there aren’t mountains to shape weather patterns. Along coasts, tropical storms and hurricanes are also hard to forecast with enough skill to integrate into reservoir operations.
As using forecasts expands, “we’ve got to be very cautious,” says Smith. Rigorous testing is required to ensure forecasts are reliable and that dams have the resources to look at and reply to changing weather. Decisions need to be made each day and sometimes hourly.
With sufficiently accurate forecasts, dam managers should see no increased risk of floods or water shortages, says Michelle Ho, a researcher on the University of Melbourne who has studied U.S. water infrastructure. And the added flexibility could help the U.S. deal with worsening drought without having to construct expensive latest infrastructure.
One thing is for certain, Talbot says: Because the climate change changes, forecasts will increasingly figure into dam management. “This represents a latest paradigm.”