Behind the Data: Tracking Groundwater

Behind the Data: Tracking Groundwater

As part of our HeadsUp! Times Square Challenge, we ask the scientists behind the data about their work and the issue of groundwater depletion.


Jay Famiglietti photo Jay Famiglietti, Director, UC Center for Hydrologic Modeling
Data set: GRACE Water Mass Data

Visualizing.org: Why should we care about groundwater levels, and what is the focus of current research and monitoring efforts?

Jay Famiglietti: Over 2 billion people rely on groundwater as their primary source of water for drinking and for growing food. However, as the data in this competition show, groundwater is being depleted at alarming rates all over the world. Most current efforts focus on measuring water levels and the quality of the water pumped from the ground. However, in many regions of the world, particularly in developing countries, even these relatively simple measurements are not made. So much research is now focusing on how to make these measurements with satellites or with inexpensive ground-based sensors.

V: The GRACE satellites measure the Earth's gravity field. How do you get from those measurements to data about groundwater? What's exciting about this data set?

JF: Water is an extremely heavy and ubiquitous substance. Consequently, when the storage in a large aquifer changes, for example, when it increases due to heavy rains, or decreases due to water withdrawal, its mass, and therefore its gravitational attraction, changes. The GRACE satellites respond to these changes and help us record which regions on Earth are gaining water and which are losing. It's easiest to think of the GRACE mission as a giant scale in the sky that helps us record how much water mass a region is gaining or losing.

The GRACE dataset is exciting for that very reason. It gives us the first global pictures of how all of Earth's freshwater availability is changing. When combined with observations on the ground, like those that Dr. Konikow has supplied, a clear picture of increasing water stress emerges.

V: What is the importance of increased public awareness of groundwater depletion, and what are some next steps we can take as a society?

JF: People need to understand where their water comes from and the threats that these supplies are facing. For example, in Southern California, about half of our water comes from groundwater. The other half comes from snowmelt in the mountains of Northern California or in the Colorado River basin, so it must be imported in canals and stored in reservoirs. Once people understand that these sources are limited—the groundwater supply is finite, while the snowpack in the western U.S. is predicted to decrease significantly with rising temperatures—then they can begin to conserve more in the home, support more efficient water use in agriculture and industry, and recognize the need for more realistic water pricing.


Leonard Konikow photo Leonard F. Konikow, U.S. Geological Survey
Data set: USGS Groundwater Depletion Rates

Visualizing.org: Your work collects many monitoring efforts into a single set of depletion rates. Where are global groundwater trends heading?

Leonard F. Konikow: The data clearly show that globally, during the past decade, groundwater use has increased and groundwater depletion has accelerated compared to most of the 20th century. This is certainly unsustainable in the long run and has caused a number of detrimental effects on the environment and on water supply. But in a number of areas in the U.S., management efforts to reduce demand, improve efficiency, and artificially recharge aquifers when possible have stabilized and even reversed long-term trends of water-level declines.

V: Your research connects groundwater depletion rates to a rise in sea level. What is the relationship? What other effects or conclusions do you hope to find in the future?

LK: Groundwater depletion means that there is less water present beneath the land surface than there was previously (my work looked at changes in groundwater from 1900 to 2008). The difference represents a large volume of water. So where is that water today? Ultimately, the great bulk of it will wind up in the oceans. After groundwater is extracted, there are many pathways it can follow—but most eventually lead to the oceans.

Travel times through streams, rivers, and the atmosphere are relatively fast, but their storage capacities are relatively small. The oceans, on the other hand, have an extremely large storage capacity. If you spread the cumulative volume of groundwater depletion—nearly equal to the volume of water in Lake Michigan—over the surface area of the oceans, it equates to a rise in sea level of more than 12 cm. This large transfer of mass from the continents to the oceans can also have some very small local and regional effects on the shape of the earth (but which can be very important for GPS technology and accuracy) and on the speed of rotation of the Earth about its axis (which can affect the length of the day by a very small amount).

V: What is the importance of increased public awareness of groundwater depletion, and what are some next steps we can take as a society?

LK: Increased public awareness of the magnitude and effects of groundwater depletion may lead to better water management policies and practices. We need to strive for a level of development that is sustainable. Although most hydrologists and other scientists are aware of the local and regional impacts of groundwater development and depletion, most are not aware that there are also some global implications, such as sea-level rise. We certainly need to encourage implementation of managed aquifer recharge whenever and wherever possible and beneficial; these programs will typically use excess runoff during wet times and inject or recharge that water into depleted subsurface aquifers through various types of engineered approaches.


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