Arquivo da tag: Água subterrânea

California drought causing valley land to sink (Science Daily)

Date:
August 20, 2015
Source:
NASA/Jet Propulsion Laboratory
Summary:
As Californians continue pumping groundwater in response to the historic drought, the California Department of Water Resources has released a new NASA report showing land in the San Joaquin Valley is sinking faster than ever before, nearly 2 inches (5 centimeters) per month in some locations.

Total subsidence in California’s San Joaquin Valley for the period May 3, 2014 to Jan. 22, 2015, as measured by Canada’s Radarsat-2 satellite. Two large subsidence bowls are evident, centered on Corcoran and south of El Nido. Credit: Canadian Space Agency/NASA/JPL-Caltech

As Californians continue pumping groundwater in response to the historic drought, the California Department of Water Resources has released a new NASA report showing land in the San Joaquin Valley is sinking faster than ever before, nearly 2 inches (5 centimeters) per month in some locations.

“Because of increased pumping, groundwater levels are reaching record lows — up to 100 feet (30 meters) lower than previous records,” said Department of Water Resources Director Mark Cowin. “As extensive groundwater pumping continues, the land is sinking more rapidly and this puts nearby infrastructure at greater risk of costly damage.”

Sinking land, known as subsidence, has occurred for decades in California because of excessive groundwater pumping during drought conditions, but the new NASA data show the sinking is happening faster, putting infrastructure on the surface at growing risk of damage.

NASA obtained the subsidence data by comparing satellite images of Earth’s surface over time. Over the last few years, interferometric synthetic aperture radar (InSAR) observations from satellite and aircraft platforms have been used to produce maps of subsidence with approximately centimeter-level accuracy. For this study, JPL researchers analyzed satellite data from Japan’s PALSAR (2006 to 2010); and Canada’s Radarsat-2 (May 2014 to January 2015), and then produced subsidence maps for those periods. High-resolution InSAR data were also acquired along the California Aqueduct by NASA’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) (2013 to 2015) to identify and quantify new, highly localized areas of accelerated subsidence along the aqueduct that occurred in 2014. The California Aqueduct is a system of canals, pipelines and tunnels that carries water collected from the Sierra Nevada Mountains and Northern and Central California valleys to Southern California.

Using multiple scenes acquired by these systems, the JPL researchers were able to produce time histories of subsidence at selected locations, as well as profiles showing how subsidence varies over space and time.

“This study represents an unprecedented use of multiple satellites and aircraft to map subsidence in California and address a practical problem we’re all facing,” said JPL research scientist and report co-author Tom Farr. “We’re pleased to supply the California DWR with information they can use to better manage California’s groundwater. It’s like the old saying: ‘you can’t manage what you don’t measure’.”

Land near Corcoran in the Tulare basin sank 13 inches (33 centimeters) in just eight months — about 1.6 inches (4 centimeters) per month. One area in the Sacramento Valley was sinking approximately half-an-inch (1.3 centimeters) per month, faster than previous measurements.

Using the UAVSAR data, NASA also found areas near the California Aqueduct sank up to 12.5 inches (32 centimeters), with 8 inches (20 centimeters) of that occurring in just four months of 2014.

“Subsidence is directly impacting the California Aqueduct, and this NASA technology is ideal for identifying which areas are subsiding the most in order to focus monitoring and repair efforts,” said JPL research scientist and study co-author Cathleen Jones. “Knowledge is power, and in this case knowledge can save water and help the state better maintain this critical element of the state’s water delivery system.” UAVSAR flies on a C-20A research aircraft based at NASA’s Armstrong Flight Research Center facility in Palmdale, California.

The increased subsidence rates have the potential to damage local, state and federal infrastructure, including aqueducts, bridges, roads and flood control structures. Long-term subsidence has already destroyed thousands of public and private groundwater well casings in the San Joaquin Valley. Over time, subsidence can permanently reduce the underground aquifer’s water storage capacity.

“Groundwater acts as a savings account to provide supplies during drought, but the NASA report shows the consequences of excessive withdrawals as we head into the fifth year of historic drought,” Director Cowin said. “We will work together with counties, local water districts, and affected communities to identify ways to slow the rate of subsidence and protect vital infrastructure such as canals, pumping stations, bridges and wells.”

NASA will also continue its subsidence monitoring, using data from the European Space Agency’s recently launched Sentinel-1 mission to cover a broader area and identify more vulnerable locations.

DWR also completed a recent land survey along the Aqueduct — which found 70-plus miles (113-plus kilometers) in Fresno, Kings and Kern counties sank more than 1.25 feet (0.4 meters) in two years — and will now conduct a system-wide evaluation of subsidence along the California Aqueduct and the condition of State Water Project facilities. The evaluation will help the department develop a capital improvement program to repair damage from subsidence. Past evaluations found that segments of the Aqueduct from Los Banos to Lost Hills sank more than 5 feet (1.5 meters) since construction.

NASA and the Indian Space Research Organisation are jointly developing the NASA-ISRO Synthetic Aperture Radar (NISAR) mission. Targeted to launch in 2020, NISAR will make global measurements of the causes and consequences of land surface changes. Potential areas of research include ecosystem disturbances, ice sheet collapse and natural hazards. The NISAR mission is optimized to measure subtle changes of Earth’s surface associated with motions of the crust and ice surfaces. NISAR will improve our understanding of key impacts of climate change and advance our knowledge of natural hazards.

The report, Progress Report: Subsidence in the Central Valley, California, prepared for DWR by researchers at NASA’s Jet Propulsion Laboratory, Pasadena, California, is available at: http://water.ca.gov/groundwater/docs/NASA_REPORT.pdf (14 MB)

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NASA Bombshell: Global Groundwater Crisis Threatens Our Food Supplies And Our Security (Climate Progress)

POSTED ON OCTOBER 31, 2014 AT 1:22 PM

Sustained droughtSustained drought in California is depleting aquifers (click to enlarge).

An alarming satellite-based analysis from NASA finds that the world is depleting groundwater — the water stored unground in soil and aquifers — at an unprecedented rate.

A new Nature Climate Change piece, “The global groundwater crisis,” by James Famiglietti, a leading hydrologist at the NASA Jet Propulsion Laboratory, warns that “most of the major aquifers in the world’s arid and semi-arid zones, that is, in the dry parts of the world that rely most heavily on groundwater, are experiencing rapid rates of groundwater depletion.”

The groundwater at some of the world’s largest aquifers — in the U.S. High Plains, California’s Central Valley, China, India, and elsewhere — is being pumped out “at far greater rates than it can be naturally replenished.”

The most worrisome fact: “nearly all of these underlie the word’s great agricultural regions and are primarily responsible for their high productivity.”

And this is doubly concerning in our age of unrestricted carbon pollution because it is precisely these semiarid regions that are projected to see drops in precipitation and/or soil moisture, which will sharply boost the chances of civilization-threatening megadroughts and Dust-Bowlification.

As these increasingly drought-prone global bread-baskets lose their easily accessible ground-water too, we end up with a death spiral: “Moreover, because the natural human response to drought is to pump more groundwater continued groundwater depletion will very likely accelerate mid-latitude drying, a problem that will be exacerbated by significant population growth in the same regions.”

So this is very much a crisis, albeit an under-reported one. But why is NASA the one sounding the alarm? How has the space agency been able to study what happens underground? The answer is that NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite mission can track the earth’s mass over space and time — and large changes in the amount of water stored underground cause an observable change in mass.

Here is California’s groundwater depletion over the last three years as observed by GRACE:

NASA GRACE

NASA: “The ongoing California drought is evident in these maps of dry season (Sept–Nov) total water storage anomalies (in millimeter equivalent water height; anomalies with respect to 2005–2010). California’s Sacramento and San Joaquin river basins have lost roughly 15 km3 of total water per year since 2011 — more water than all 38 million Californians use for domestic and municipal supplies annually — over half of which is due to groundwater pumping in the Central Valley.”

Certainly, the combined threat of mega-drought and groundwater depletion in the U.S. breadbaskets should be cause for concern and action by itself.

But we should also worry about what is happening around the globe, if for no other reason than it inevitably affects our security. As I wrote last year, “Warming-Fueled Drought Helped Spark Syria’s Civil War.”

Dr. Famiglietti explains the risk:

Further declines in groundwater availability may well trigger more civil uprising and international violent conflict in the already water-stressed regions of the world, and new conflict in others. From North Africa to the Middle East to South Asia, regions where it is already common to drill over 2 km [kilometers] to reach groundwater, it is highly likely that disappearing groundwater could act as a flashpoint for conflict.

Outside of this country, NASA has observed aquifer declines in “the North China Plain, Australia’s Canning Basin, the Northwest Sahara Aquifer System, the Guarani Aquifer in South America … and the aquifers beneath northwestern India and the Middle East.”

GroundwaterDepletion

Water storage declines (mm equivalent water height) in several of the world’s major aquifers.

Famiglietti says that groundwater “acts as the key strategic reserve in times of drought, in particular during prolonged events,” such as we’re seeing in the West, Brazil, and Australia:

Like money in the bank, groundwater sustains societies through the lean times of little incoming rain and snow. Hence, without a sustainable groundwater reserve, global water security is at far greater risk than is currently recognized.

Yes, we can stave off bankruptcy a little longer despite our unsustainable lifestyle by taking money from our children’s bank accounts. As we reported last year, we’re taking $7.3 trillion a year in natural capital — arable land, potable water, livable climate, and so on — from our children without paying for it. In short, humanity has constructed the grandest of Ponzi schemes, whereby current generations have figured out how to live off the wealth of future generations.