Newly released images created from NASA satellite data illustrate the staggering effect the California drought has had on groundwater supply in the state.

The images show the amount of water lost over the past 12 years, with different colors indicating severity over time.

According to NASA, the Sacramento River and San Joaquin River basins have been hit the hardest by the water loss, in part because of the increasing volume of groundwater being pumped out for farming. For the last three years, these regions have been losing a total of 4 trillion gallons of water per year.

The data was compiled from two satellites that have been orbiting the Earth since 2002 as part of the Gravity Recovery and Climate Experiment (GRACE) mission, a collaboration between NASA and German space agency DLR. The satellites measure small fluctuations in Earth's gravitational field that are most often caused by variations in water supply.

In a podcast interview with Science Magazine, UC Irvine hydrologist James Famiglietti used the analogy of a bathroom scale to explain how GRACE uses highly sensitive gravity measurements to track changes in the amount of water stored underground in soil and rocks.

"Each [satellite] is about the size of a squashed minivan, and they orbit at about 400 kilometers. And what happens is that the change in mass on the surface, say, because of a big flood or a big load of snow on the mountains, actually pulls those spring-loaded weights towards Earth's surface," Famiglietti said.

The added danger in groundwater depletion is that unlike surface water, it is not easily replenishable. A UC Davis study published in July demonstrates how California farmers draining groundwater to compensate for losses in surface water will diminish the state's ability to withstand future droughts.

California is currently experiencing the third year of one of the most severe short-term droughts ever recorded. Data from U.S. Drought Monitor shows that as of Sept. 30, 82% of the state is facing extreme or exceptional drought conditions.

But the state is not the only area being plagued by critical drops in groundwater reserves. Data collected by GRACE indicates that the supply of groundwater is in decline worldwide, especially in regions that rely on it most.

"We're seeing it happening all over the world. It's happening in most of the major aquifers in the arid and semi-arid parts of the world where we rely on those aquifers. But we're able to see now the impact we're having on this over exploitation," Famiglietti told Science Magazine.