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Gravity. It keeps Earth

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orbiting around the Sun, satellites in Earth’s orbit and all of us 

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standing on the ground. Gravity also allows us to track how 

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water moves around our home planet. By measuring minute 

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changes in gravity from space, the Gravity Recovery and Climate Experiment, 

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or GRACE mission, and its successor, GRACE Follow-on, have helped us

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follow water moving on and below Earth’s surface for more than 15 years.

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Now, integrating these and other measurements 

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into advanced computer models allows researchers to distinguish water

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in the soil, root zone and deeper in the ground – and to forecast

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into the future. Working with the National Drought Mitigation Center, 

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NASA scientists are providing global water availability maps 

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and U.S. forecasts to the public. The forecasts look

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30, 60 and 90 days into the future and allow farmers, 

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community managers and researchers to prepare for flash droughts and floods. 

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The ability to forecast where water will be comes from knowing 

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where water has been, measuring soil moisture and how much water has been gained

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or lost from aquifers. Using the models to separate the water

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into layers, we can better predict events like flash floods, which are more likely 

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when the surface soil is already saturated, and anticipate droughts

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as aquifers run out of water and take time to recharge. 

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Among the layers, surface soil moisture responds most rapidly to the weather, 

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while root zone soil moisture – the water available to plants – changes more 

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slowly, and groundwater – a vital resource for drinking water

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and agriculture – evolves over months and longer.

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Like here in the Okavango Delta. In the 25 years before 

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GRACE launched, the region experienced a prolonged drought. 

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Around the time GRACE started collecting data in 2002

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precipitation picked back up. While the soil moisture quickly responded, it took longer 

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for the aquifers to refill.Although groundwater is not immediately

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immediately affected by drought, it also takes longer to recover from drought.

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In Australia, a historic drought in the early 2000s impacted

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all of the layers. Another drought at the end of 2019 

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was seen by the GRACE-FO mission and dried out vegetation in the region, 

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leading to intense fires that burned through early 2020. 

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Let’s take another look at Europe. A heatwave scorched western Europe, 

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melting glaciers and drying out the region. Soil moisture dries 

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up almost immediately, while the root zone, which crops rely on, takes 

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longer to catch up. This computer model, by assimilating

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satellite observations, helps monitor drought and wetness conditions.

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NASA scientists originally developed the capability for the United States, 

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but it is now providing valuable information on the whole world. 

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Combining NASA’s spaceborne view with research and high end computing

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helps us better prepare for extremes in water availability.

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EXPLORE
EARTH

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NASA