Sacramento: The Nation's Next Urban Flood Disaster?

March 2008
Deep snow at visitor center.
Credit: NOAA

By Feb. 5 of this year, nearly eight feet of snow had fallen on this U.S. Forest Service's summer visitor center in Tahoe National Forest northeast of Sacramento.

West Coast winter storms may lack the "star power" of East Coast hurricanes. They aren't named at birth or routinely tracked by the media. But the impact of these western cyclones, spawned over Earth's largest ocean and nourished by long ribbons of moisture from the tropics, can be even more devastating than their famous cousins back East. Huge, soggy systems slam the coast with torrents of rain, powerful winds, and -- at higher elevations -- deep snows. Widespread power outages, flooding, and debris flows can follow, rivaling the destruction of major hurricanes.

In the path of these storms lies the city of Sacramento, deep in the flood-vulnerable basin of the American River and downstream from the massive Folsom Reservoir. A second large river, the Sacramento, flows along the western edge of the city.

Folsom dam
Credit: U.S. Bureau of Reclamation

Folsom Dam, built on the American River near Sacramento in 1955, contains up to a million acre-feet of water.

A system of levees protects the city from inundation by the rain-swelled rivers. One or more levees giving way could drown parts of Sacramento under 20-plus feet of water. One big miss on a major storm forecast may be all it takes to catch water managers off guard and turn a background risk into nightmarish reality.

Hydrometeorology Testbed

To prevent such a disaster, NOAA's Earth System Research Laboratory (ESRL) is funneling years of West Coast storm research into the Hydrometeorology Testbed -- a combination of high-tech sensors and brainpower aimed at the Sacramento area. ESRL researchers are working closely with NOAA's National Weather Service forecasters and other partners to provide the data, tools, and understanding needed to develop high-precision weather forecasts with longer lead times. "We need to be able to say with confidence, A week from now we're expecting a flood that will significantly threaten the levees,'" said HMT project manager Tim Schneider.

"We need to be able to say with confidence, A week from now we're expecting a flood that will significantly threaten the levees"
-- Tim Schneider, HMT project manager.

Satellite image of inhanced precipitation.
Credit: NOAA

Satellite data taken Dec. 3, 2007, showing a long ribbon of moisture, or "atmospheric river," as it hit Ore. and northern Calif.

For three winter storm seasons, NOAA has deployed an assortment of radars, wind profilers, rain and snow gauges, automated weather stations, and other sensors along the north fork of the American River, turning its basin into one of the most monitored areas in the country. Daily weather balloon launches increase from twice a day to every three hours during severe weather observations.

Aircraft Improve Observations and Lead Time

This year one of NOAA's off-duty Hurricane Hunter aircraft will fly into the huge storms when they're still distant over the Pacific, gathering data specially requested for the Hydrometeorology Testbed, among other observations.

In 2009 a fleet of robotic aircraft, including a high altitude, long-endurance Global Hawk and smaller, lower-altitude vehicles, will fly below, into, and above the storms. NOAA researchers are testing the vehicles' ability to gather data unattainable by manned aircraft and help fill in the missing pieces needed for better West Coast forecasts.

Flood debris.
Credit: U.S. National Forest Service

More than 30 inches of rainfall over several days caused major flooding and debris flow from the White River in Ore.

"What keeps me awake at night is the thought of seeing Sacramento under water"
-- Marty Ralph, NOAA/ESRL scientist.

"What keeps me awake at night is the thought of seeing Sacramento under water," said NOAA/ESRL scientist Marty Ralph, who led the core research behind the testbed and manages NOAA's Unmanned Aircraft Systems program. "Here at NOAA we're doing all we can to develop the best forecasts possible to prevent that kind of catastrophe."

East Coast hurricanes may get the media glare in late summer, but for the next few winters NOAA will be shining its own spotlight on these powerful Pacific storms and the safety of those living in their path.

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