GRACEfully Managing Groundwater from Outer Space

NASA

GRACEfully Managing Groundwater from Outer Space

Groundwater managers have a difficult time getting a sense of how much water farmers and urban water users extract from aquifers. Gravity Recovery and Climate Experiment (GRACE) is a satellite technology that uses microwaves to generate data that researchers use to build Earth gravity models. The models produced from GRACE data help water managers know how much water farmers and urban water planners have withdrawn from the ground. This helps communities manage their groundwater resources sustainably.

Werth, S., White, D., & Bliss, D. W. (2017). GRACE detected rise of groundwater in the Sahelian Niger River basinJournal of Geophysical Research: Solid Earth122, 10,459-10,477. https://doi.org/10.1002/2017JB014845

The California as we know today would not exist without groundwater. 85% of Californians get some part of their water supply from the ground through wells. However, a high dependence on groundwater and poor management has led to over-exploitation of this essential resource. In 2017, after a five year drought, over 3,000 domestic wells went dry in California.

Groundwater is connected to surface water in the same way that a savings account links to a checking account. Overdrawing one resource will deplete the other. The more water farmers pump from the ground, the less water runs in the rivers and streams.

As rainfall patterns become more unpredictable and the world becomes warmer due to climate change, cities that rely on surface water might have to start depending more on groundwater stocks (the savings account) to make up for empty lakes and dry rivers. This will further strain groundwater resources. What tools are available to help water planners effectively monitor groundwater resources?

A new study in The Journal of Geophysical Research: Solid Earth details how researchers at Arizona State University used GRACE, to detect groundwater changes in the Sahelian Niger River Basin in Africa. These researchers aimed to track the long-term changes in groundwater in the Niger River Basin to improve Niger’s water management strategies. GRACE is a remote sensing technology that uses satellite microwaves to generate data that scientists use to build Earth gravity models. NASA, the National Aeronautics and Space Administration, and the German Aerospace Center created the satellite technology in a joint effort. The Earth gravity models that are created with the help of GRACE can aid groundwater administrators in keeping track of how much groundwater farmers and urban water users extract from the ground. Although this study focuses on the Sahelian Niger River Basin, water managers in groundwater-dependent California have also adopted this technology.

The GRACE mission consists of two satellites that move in unison like ballroom dancers, except that there’s a large distance between the satellites. If the first satellite encounters an area with a strong gravity pull, it will diverge from its path. As the second satellite passes through the same area, it mimics the first satellite’s movement like ballroom dancers responding to each other’s moves. During this in-sync movement, the satellites simultaneously measure the changes in distance between each other. Each month, scientists use the data from these satellites to generate models of Earth’s gravity. They then analyze these changes in the Earth’s gravity to extrapolate changes in groundwater levels.

Data gathered from GRACE can help water managers in regions that are highly dependent on groundwater make better resource management decisions. GRACE’s launch has allowed hydrologists to move away from expensive and time-consuming field data collection.

As with all technologies, GRACE has room for improvement. For example, the spatial resolution of GRACE data is capable of processing data that are 200,000 km2 and larger. Spatial resolution refers to how clearly one can see an image after zooming in. If GRACE tries to zoom in beyond 200,000 km2, which is about the size of South Dakota, it produces grainy pixelated images that are hard to see.

NASA and the German Aerospace Center – guardians of GRACE – extended the GRACE mission by launching GRACE-Follow On, affectionately known as GRACE-FO, after decommissioning the original GRACE satellites. This means that water managers will continue to benefit from the data produced by this mission. In an age in which climate change-induced water scarcity has left cities like Cape Town in dire need for water, it becomes increasingly important to wisely manage our water resources. Ultimately, all life depends on water and without it, life stops!

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