Earth Science & Climate Monitoring | NASA Lends a Hand in Parched California

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SAN FRANCISCO — When researchers at NASA’s Jet Propulsion Laboratory began measuring snow levels in a Sierra Nevada mountain river basin in April 2013, operators of the reservoir below showed little interest in their plans because they already obtained detailed data on the snowpack from pillows designed to measure the weight of snow and tubes plunged into the snow at regular intervals. “They said we are not going to use your data,” said Tom Painter, principal investigator for the Airborne Snow Observatory at Pasadena, Calif.-based JPL. 

Nevertheless, Painter’s team provided reservoir operators with information obtained during weekly flights of a de Havilland Twin Otter aircraft equipped with two instruments built by Canadian firms, a scanning lidar from Optech Inc. to measure snow depth and an imaging spectrometer from ITRES to measure snow reflectivity, which helps researchers estimate how quickly it will melt. 

“As it got on later in the season, the operators began to realize the water flows were dropping more quickly than they anticipated,” Painter said. 

Eventually, reservoir managers began using data drawn from the NASA mission to determine when water could be released into a dam to generate hydroelectric power and when it should be retained in the reservoir, he said.

The Airborne Snow Observatory was one of four projects described by NASA and California officials in a Feb. 25 briefing on work the agency is performing to help the state monitor water resources and assess the impact of one of the driest years on record. California Gov. Jerry Brown declared a state of emergency Jan. 17 and called for statewide water conservation measures. Brown also directed the California Department of Water Resources (DWR) to refine climate forecasts and evaluate the impact of scarce rain and snowfall. 

NASA’s work with the DWR predates the current crisis. The two agencies began cooperating in 2009 with funding provided by the American Recovery and Reinvestment Act. Since then, “this partnership has been blossoming,” said Lawrence Friedl, director of NASA’s Applied Sciences Program. 

DWR is helping NASA officials understand the types of data it needs to better manage its water supply, while NASA is demonstrating to DWR the utility of existing remote sensing tools and informing California officials of additional data the agency plans to draw from the U.S.-Japanese Global Precipitation Measurement satellite launched Feb. 27 and NASA’s Soil Moisture Active Passive Mission satellite scheduled for liftoff in November, Friedl said. 

In April, NASA plans to resume weekly Airborne Snow Observatory flights over Yosemite National Park’s Tuolumne River Basin, the primary source of drinking water for the San Francisco Bay area. “We do this across an entire basin in a day and give that information to water managers within 24 hours,” Painter said. 

Information gathered by the NASA mission helps state officials measure the amount of water contained in the snowpack, determine how the snowpack changes from week to week, and estimate the timing and magnitude of spring and summer melting, Painter said. The JPL team would like to expand the mission to survey the snowpack in the entire Sierra Nevada range, he added. 

NASA also is working with the U.S. Geological Survey and the U.S. Department of Agriculture to use data from the Landsat 7 and Landsat 8 Earth imaging satellites as well as the space agency’s Terra and Aqua environmental monitoring spacecraft to survey California farmland that remains idle due to the drought. 

“For the first time, we will be providing consistent accurate in-season estimates of fallowed acreage across California using satellite data,” said Forrest Melton, senior research scientist at the Cooperative for Research in Earth Science & Technology at the NASA Ames Research Center in Mountain View, Calif. “We can obtain information for every field in the state once every eight days. We can also develop a time series showing how the vegetation is tracking as the year progresses.” 

The state uses that information for drought mitigation and emergency response planning. For example, California’s Department of Food and Agriculture may use it to identify areas likely to require additional food banks, said Jeanine Jones, DWR’s interstate water resources manager.

In addition, NASA is conducting a campaign to help state officials identify places where the ground is sinking as water is drawn from wells or aquifers below. Traditionally, Californians pump groundwater in the summer and the state’s aquifers refill with the winter rains. The recent long-term decrease in rainfall is preventing replenishment of the aquifers and causing the land above them to sink.

NASA is using interferometric synthetic aperture radar images taken weeks, months or years apart to measure the extent of surface deformation. The data help water managers gauge the condition of aquifers and identify areas where sinking ground levels are likely to cause problems for major infrastructure projects, such as California’s planned high-speed rail, said Tom Farr, a JPL geologist.

Other NASA projects are designed to improve weather forecasts. NASA officials are studying atmospheric rivers, which are long, narrow tunnels of water vapor that carry moisture from the tropics to the western United States. Researchers from NASA and the U.S. National Oceanic and Atmospheric Administration have discovered that a single atmospheric river can transport as much water as five to 10 Mississippi Rivers with 20 to 30 percent of that water producing rainfall in coastal areas and snowfall in the Sierra Nevada.

“Atmospheric rivers drive heavy precipitation events,” said Duane Waliser, chief scientist at JPL’s Earth Science Technology Directorate. “They account for 30 to 40 percent of the fresh water supply in the west.”

Researchers are looking for ways to improve forecasting of atmospheric river intensity, timing and location. Existing tools only allow researchers to determine where these rivers are likely to reach land within 500 to 600 kilometers five days before the event occurs. More precision is needed because that means forecasters do not know if major storms are headed for San Francisco or Los Angeles, Waliser said. 

Taken together, the various water-related research projects are likely to help California develop a comprehensive picture of its most precious resource. 

“We are starting to fit pieces of the puzzle together,” Farr said. “Then we can actually start thinking about the fact we are measuring every aspect of the hydrological cycle in a region like California.”