Satellites used to map water risk
A satellite and sensing project is helping scientists track groundwater depletion globally. The GRACE project comprises twin satellites that track changes in groundwater from space, by detecting shifts in gravity.
As the satellites orbit the earth, one crossing a given point 171km to 311km in front of the other, they constantly monitor the distance between them with incredible accuracy.
The first satellite moves up and down depending on the amount of mass on Earth below it. The greater the mass beneath it, the more gravity acts upon the satellite, and the farther down it moves.
Water is especially heavy, so depletion of a water-rich aquifer will cause a mass loss that will lessen gravity’s tug on the satellites, allowing them to drift a tiny bit further away from Earth. The Water Resources Institute (WRI), which is managing the project, says that the small movements of the GRACE satellites are detectable, even if they are only one-tenth the width of a human hair.
Using satellite data from NASA, researchers have created an accurate database of groundwater-storage change in water basins by monitoring how much the distance between the satellites changes on a month-to-month basis.These satellites provide transparency and necessary data that can make up for the lack of on-the-ground monitoring of water resources around the world.
“GRACE and other satellite projects like it are opening new frontiers for water resources management,” said Betsy Otto, director of WRI’s Aqueduct project.
One example is the Middle East’s Tigris-Euphrates basin, which experienced significant drought in 2007. Simultaneously, GRACE satellites detected decreasing groundwater levels in northern Iraq.
Researchers learned that Turkey’s well-developed canal and reservoir infrastructure could store enough water to sustain crop yields during the drought, but Syria and Iraq had no such infrastructure. Their farmers were forced to draw on groundwater.
Agricultural yields in Syria and Iraq plummeted after 2007. Turkey – the upstream user– refused to release additional flows to the neighbouring countries, and water stress became so severe that some farmers abandoned their lands and migrated to Baghdad. As of this year, the region had the second-fastest rate of groundwater depletion on Earth, after India.
Kate Voss, policy fellow at the University of California Center for Hydrologic Modeling(UCCHM) said that researchers in Turkey have at times refused to release their water-related data, citing security concerns, but the GRACE remote-sensing technology has created a bypass around the reluctance of many countries to release their data.
GRACE scientists are now teaming up with researchers on the Aquaduct project, which has developed a global water risk mapping tool that helps companies, investors, governments, and other users understand where and how water risks and opportunities are emerging worldwide.
WRI says that the next step toward better water management is contextualising and translating this information into user-friendly online tools. Professor Jay Famiglietti, director of the UCCHM will lead the workto incorporate this new groundwater data into Aqueduct’s interactive water maps and global water risk assessment tool.
Voss said: “You link something [like GRACE] into Aqueduct, where you combine the hydrologic data with other indicators and socioeconomic factors, and I think it becomes a really powerful tool.It becomes leverage for water managers and for politicians to hopefully start acting.”
“Water in trans-boundary river basins must be managed efficiently, equitably, and sustainably,” said Charles Iceland, senior associate for WRI’s Aqueduct project. “This is not possible without data openness and transparency.”
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