Where does all the water go?

Groundwater aquifers are extremely important sources and storage reservoirs of fresh water, especially in regions experiencing severe droughts that can rapidly diminish surface-water supplies. Unsustainable groundwater use can have detrimental effects such as aquifer depletion, loss of storage capacity, chemical and waste contamination, saltwater intrusion, and rapid land subsidence. Thus, it is essential to accurately track changes in the distribution of groundwater to manage the use and replenishment of these water systems below Earth’s surface. However, conventional groundwater measurements are limited in their ability to map out the spatiotemporal state of aquifers, which makes it challenging to track groundwater storage. On page 758 of this issue, Mao et al. (1) report how groundwater storage distribution can be monitored in both space and time through measurements of seismic ground vibrations or noise. This approach should enable surveillance of the amounts of subsurface water and enhance the management of sustainable groundwater use.