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the food we eat has changed a great deal

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in the last century from the kind of

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food we grow to the farms it's grown on

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to the process of getting it from

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but one of the biggest changes to global

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agriculture isn't so much about the food

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itself it's about the water we use to

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grow it over the past century we've gone

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from a situation where farmers dependent

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almost exclusively on rainfall for their

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crops to a realization that they could

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use irrigation to maximize crop output

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and grow crops in areas that may be too

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dry or where they would naturally be

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able to grow that shift comes with new

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responsibilities in some areas people

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are using water faster than its being

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replenished NASA satellites help us see

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how water moves from ocean to atmosphere

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to land where we harness it for growing

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food the big picture view they provide

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helps us understand how our water needs

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are being met today and where we might

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increasingly we're tapping into ground

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water from underground aquifers to meet

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our demand these aquifers vast regions

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of water saturated earth can be huge but

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hidden underground they're difficult to

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observe how do you study what you can't

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pair of satellites called grace is on a

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special mission they're carefully

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mapping delicate variations in the

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Earth's gravity our planets gravity

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isn't the same everywhere objects with

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larger mass mountain ranges for instance

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exert a stronger pull

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so two huge bodies of water like

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aquifers as the grace satellites orbit

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together large objects affect the

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leading satellite before they affect the

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trailing one causing the distance

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between to vary by taking continuous

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measurements of that distance scientists

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can map the Earth's gravity field and

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see how it changes over time and over

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land the major cause of that variability

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is changes in the amount of ground water

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grace effectively feels those changes by

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monitoring gravity changes in

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groundwater are actually sensed by grace

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and we can come up with asked of the

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water table variations and that's what

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we did for Northwest India in India

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water hungry farms in the nation's North

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draw 95% of their water from ground

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water stores since grace is launched in

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2002 aquifers beneath Northwest India

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have lost a staggering amount of water

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three times as much water as is held in

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Lake Mead America's largest reservoir is

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gone the people of India know this is

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happening they know this because their

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wells occasionally run dry and if you

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dig a deeper well in some cities the

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wells are running dry so fast that

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people spend their entire day trying to

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find a clean source of water for their

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for their family if the aquifer

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continues to decline the region's

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agriculture faces an uncertain future as

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do the almost 115 million people who

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live there India is not alone other

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major aquifers like those beneath

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northern China and the central US are

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also in decline water is critical to

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people minutes of it's a vital resource

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obviously so being able to understand

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the water cycle and how it's changing is

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important as we move forward in the

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highly populated world with potential

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climate change going on and

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NASA satellite survey shion's are

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extremely valuable to getting an

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unbiased view of what's going on with

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Water Resources will become even more

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scarce in the coming century the grace

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satellites can't help us recoup what

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we've lost but they do give us something

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valuable knowledge we can use to shape