Groundwater is the water found underground in the cracks and spaces in soil, sand and rock. Groundwater accounts for more than half of the U.S. drinking water and crop irrigation, and a source of recharge for lakes, rivers, and wetlands. It’s stored in geologic formations of soil, sand and rocks called aquifers.
This map was created using satellite data and ground-based measurements to model the relative amount of water stored in underground aquifers in the continental United States on July 7, 2014, compared to the average from 1948 to 2009.
Areas shown in blue have more abundant groundwater for this time of year than comparable weeks over the long-term, while shades of red depict deficits compared to this time of year.
The measurements used to create these kinds of maps are derived from observations of small changes in Earth’s mass and its gravity field — features that are affected by the movement and storage of water and ice around the planet.
The extent of drought in the U.S. Southwest are reflected well in the map. California, Nevada, New Mexico, Colorado, Texas, Arizona, Oklahoma, and Nebraska have been suffering from various degrees of long-term drought that has parched the land surface and prevented the replenishing of groundwater below.
However, some other odd juxtapositions appear. The Pacific Northwest states of Oregon and Washington are suffering through raging wildfires, as months of hot weather have dried out forests. But according to the groundwater data, conditions underground are normal to wet—likely a reflection of the long lag between the accumulation and depletion of water underground and the changes in conditions on the surface. Those states had very wet winters, but the heat and dryness of spring and summer have not yet penetrated the underground storage.