NASA Finds Massive Water Loss In Central Valley
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On Monday NASA announced since October 2003, "the aquifers for California's primary agricultural region--the Central Valley--and its major mountain water source--the Sierra Nevadas--have lost nearly enough water combined to fill Lake Mead, America's largest reservoir." Based on data from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE), Sacramento and San Joaquin drainage basins have together lost more than 30 cubic kilometers of water. A cubic kilometer is about 264.2 billion gallons, which is enough to fill 400,000 Olympic-size pools.
GRACE-based findings are being presented by scientists from NASA and the University of California, Irvine, this week at the American Geophysical Union meeting in San Francisco. Matt Rodell, who leads the team of hydrologists at NASA's Goddard Space Flight Center, spoke to reporter Len Ly in a phone interview Tuesday about the findings' impact.
Obviously California lost a lot of water, enough to fill Lake Mead--America's largest reservoir. Are you surprised at the results GRACE found?
We're not particularly surprised because we've seen other reports. I think what's amazing is that we can measure the water shortage change using satellites.
Are the causes for the depletion rates primarily caused by pumping groundwater at excessive rates?
That's correct. Groundwater is really a limited resource. It's replenished annually so there is only a particular amount of water you can use safely without any dangers to limiting water in your region. But when you start to pump more water than it is available naturally--that can be naturally replenished--then you get into the situation where water can be depleted over time.
More recently, there has been a drought in the region and it actually exasperated the problem. People become more reliant on groundwater when there is not as much surface water available so it's sort of a double whammy.
So lack of natural groundwater and excessive pumping are primary contributors to the depletion rate. What's the worst case scenario? Do you have a prediction of when water will run out if the trends continue?
We cannot predict when water will run out. We can only measure the changes on a monthly or on an annual basis. There's not just imminent danger of water running out, but over time if more water is pumped than it is replenished, you start to have water tables declining; people have to dig deeper and deeper wells, which is expensive. Water quality will decline and it will become more saline. So it's a situation that becomes worse and worse.
The GRACE satellite system can predict droughts correct? Do you know where the next droughts are going to be?
I wouldn't say GRACE can predict droughts. They can show us where there's a current or depths of water. GRACE can help us see places where perhaps they're prime for a drought.
A major drought in the U.S. would cost us $6 to $8 billion dollars annually?
$6 to $8 billion annually is an average amount of economic impact of droughts in the U.S. each year.
GRACE satellites studied other regions before you got the California results . . . any good news from what GRACE found?
[Laughs] Well we have seen a severe drought in the southeastern United States in 2007 and 2008, and it got a good amount of precipitation starting in about January of 2009. They have actually come out of that drought so that has been reflected in the GRACE data.
Did GRACE findings show we're out of the drought in the California regions?
Not completely. The drought has gotten a little better maybe. We'll see which direction it goes from here.
Mr. Rodell, your advice to legislators?
[Laughs] I'm a scientist so I try to stay out of policy. I hope the legislators will pay attention to the findings that we have. Look at the data that we provided and that'll help them make informed decisions.
The GRACE satellites, they're still going to be studying the water regions?
The GRACE satellites are still flying and we hope they'll be up for another few years. What we're really hoping is to have a follow-up mission, a version of GRACE could be put up sometime in the next decade.
In addition to California, GRACE also revealed groundwater levels in northwest India have declined by 17.7 cubic kilometers per year over the past decade, due greatly to groundwater pumping and consumption. Australia, the Middle East-North Africa region and the southeastern United States are also under study. More information about the GRACE-based findings and other NASA reports from this week's AGU meeting can be found here.
