From space, we track water in the ground – whether it is a centimeter, a meter, or a kilometer below the surface.
Around the world, NASA's GRACE satellites have provided unprecedented views of water storage in natural aquifers. These underground reserves are so massive that they affect Earth's gravity field. When their mass changes, the satellites detect the change in gravity.
Droughts can affect deep groundwater stores when water users pump hundreds of billions of gallons out of their aquifers to compensate for the lack of rainfall – and GRACE can detect this change.
This view from space has revolutionized our understanding of water stores beneath the surface. But scientists at NASA Goddard can combine GRACE data with sophisticated computer models to give decision makers in the continental US an otherwise unseen view, helping to trigger critical water conservation measures.
These computer models help us decompose the GRACE signal to identify changes in both the shallow groundwater and the root zone where crops are actually drawing moisture to survive.
Stations on the ground provide a connect-the-dots picture. The vantage point from space – combined with modeling – provides a comprehensive view of how the drought evolved over time and ultimately ended.
This constantly changing snapshot of shallow groundwater conditions is now used every week in the US Drought Monitor, the benchmark relied upon by decision makers at the local, state, and federal level.
This visualization shows the global Terrestrial Water Storage Anomaly from GRACE data, and then highlights the contiguous United States to show groundwater anomaly. This more detailed view is made by assimilating GRACEwater storage data into a supercomputer model of the land surface. The visualization dives into California, showing further detail by separating out the surface soil moisture (top 2 centimeters) and the root zone soil mositure (top 100 centimeters).