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Around the world, water

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is constantly moving. From 2002 to

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2016. a pair of NASA satellites witnessed massive shifts

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in the freshwater stored on land related to water management, climate change

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and natural cycles. The Gravity Recovery and Climate Experiment,

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or GRACE mission, used precise measurements of the motions of two

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spacecraft in Earth’s orbit to track the movement of water through the oceans, land

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and atmosphere. NASA scientists combined GRACE

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data with satellite-based observations of precipitation and crop irrigation,

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climate model predictions, and other information in order to identify

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the causes of regional trends in freshwater storage.

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In this visualization, blues indicate areas with more stored freshwater

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than the average, and oranges and reds denote areas with less.

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The science team classified the major trends observed by GRACE as driven by:

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Natural variability, human activity or climate change.

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For instance, the steady decrease

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in freshwater storage in Greenland is caused by the melting of glaciers,

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which drain water into the oceans.

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In the western United States, a long drought reduced mountain snowpack and river flows,

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causing heavy reliance on aquifers for crop irrigation and

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severe depletion of freshwater resources.

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Precipitation measurements together with GRACE data show how natural variations

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in the weather and unsustainable rates of water use conspired to deplete

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groundwater in California.

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In southern Africa, the Okavango Delta region experienced a huge

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increase in stored freshwater during the period of the GRACE mission.

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The science team analyzed precipitation data for the area and found that it was caused

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by a pronounced increase in rainfall.

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Between 2004 and 2012, the region saw about 15% more

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annual rainfall than during the previous twenty-five years.

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The rain ended a regional drought, and replenished water storage in the area.

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In northern Saudi Arabia, GRACE detected a dramatic

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decrease in fresh water stored in aquifers. Images taken by

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NASA’s Landsat program show a rapid increase in irrigated cropland,

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supported by water pumped from those aquifers.

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Most of that water is non-renewable on human timescales, but in 2014

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the Saudi government ended a domestic wheat farming program, and GRACE data

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suggest that aquifer levels may be stabilizing.

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In northwest China, GRACE revealed a rapid

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decrease in freshwater storage without an obvious cause.

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Scientists knew that mountain glaciers were melting, but the melt-water did not leave the region,

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so they looked for another explanation.

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As it turns out, much of the region’s surface water is redirected to

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agricultural areas and the desert to the south, where it evaporates,

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leaving the region with a net loss of water.

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The original GRACE satellites stopped operating in 2017,

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but NASA and the German Research Center for Geosciences are partnering to launch a new

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satellite pair, GRACE Follow-On, in late spring 2018

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to continue providing data about freshwater trends around the world.

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