California's Two Largest River Basins At Near-Record Low Water Levels
February 3, 2014

California’s Two Largest River Basins At Near-Record Low Water Levels

[ Watch the Video: ScienceCasts: California Drought ]

Brett Smith for - Your Universe Online

In response to Governor Jerry Brown’s recent proclamation of a drought emergency in California, a team of scientists from the UC Center for Hydrologic Modeling (UCCHM) at the University of California, Irvine has updated research on the state’s two largest river basins -- the source of most its water.

The updated evaluation showed that California's Sacramento and San Joaquin River basins have reached near decade-low water holding levels.

The region investigated by the scientists also includes the Central Valley, the most prolific agriculture region in the country. The Central Valley depends completely on the surface and groundwater resources inside the river basins to fulfill its irrigation needs and to grow food for the nation.

Using NASA satellite data, the scientists discovered that as of November 2013, total water held in the river basins -- a combination of all of the snow, surface area water, soil moisture content and groundwater, along with an integrated gauge of basin-wide water supply -- had diminished to its lowest point in almost a decade. Satellite data for the record-dry 2013-2014 winter months were not yet available for the investigation.

The data show significantly steep water deficits between November 2011 and November 2013, the beginning phase of the current drought. The UC Irvine scientists estimated that the basins have already lost 2400 cubic miles of freshwater in each of the previous two years -- comparable to almost all of California’s annual urban water use.

The scientists pointed out that snowpack, surface water and soil moisture in the river basins were all at their minimum points in virtually a decade, showing a developing threat to groundwater supplies in the Central Valley, and displaying the immediate need to handle them sustainably. Groundwater is usually considered a strategic reserve that supports short surface water supplies in times of drought.

By incorporating their satellite data from October 2003 through November 2013 of Central Valley groundwater storage shifts with long-term estimates of groundwater deficits from the US Geological Survey, the scientists noted that steep drops in groundwater storage are common during droughts, when Central Valley farmers are pushed to rely more heavily on groundwater to meet irrigation needs.

The advisory report emphasized that the rates of falling groundwater storage during drought typically outpaces rates of groundwater recovery during wet periods, and raised fears about the effect of long-term groundwater exhaustion on sustaining a dependable water supply in the existing, record-setting drought. The team’s 2011 study estimated that the Central Valley lost almost 4,800 cubic miles of groundwater during the 2006-2010 drought.

Traditionally, drought conditions and groundwater exhaustion in the Central Valley are accountable for widespread land subsidence, cutbacks in planted acreage, increased food costs and environmental damage.

If the drought continues, "Central Valley groundwater levels will fall to all-time lows,” said UCCHM Director and UC Irvine earth sciences professor Jay Famiglietti.

Report author Stephanie Castle, a UCCHM researcher, said California groundwater supplies should be more actively managed and added that "the path of groundwater use that we are on threatens the sustainability of future water supplies for all Californians.”