Satellites Reveal the Gains and Losses of California’s Groundwater

California has experienced severe droughts and water shortages in the past decade, affecting millions of people, agriculture, ecosystems, and wildlife.

However, thanks to a wet winter in 2022 to 2023, the state saw significant gains in its water resources, as measured by satellites from the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission.

GRACE-FO: a unique view of water on Earth

(Photo : GUILLERMO ARIAS/AFP via Getty Images)

GRACE-FO is a joint mission between NASA and the German Research Centre for Geosciences (GFZ), launched in May 2018.

It is a successor to the original GRACE mission, which operated from 2002 to 2017.

GRACE-FO consists of two identical satellites that orbit the Earth about 220 kilometers (137 miles) apart.

The satellites use micro wave and laser instruments to precisely measure the distance between them, which changes as they fly over areas with different amounts of mass.

As water moves around on Earth -- in the form of rain, snow, ice, rivers, lakes, groundwater, and oceans -- it changes the distribution of mass on the planet's surface.

This affects Earth's gravity field, which slightly pulls or pushes the satellites as they pass over different regions.

By measuring these tiny variations in gravity, GRACE-FO can estimate changes in the total amount of water in a given area over time

GRACE-FO data can reveal how much water is stored in different reservoirs on land, such as snowpack, soil moisture, surface water, and groundwater.

It can also show how much water is lost or gained due to natural processes or human activities, such as precipitation, evaporation, irrigation, pumping, or damming. GRACE-FO data can also help monitor changes in sea levels, ice sheets, and glaciers.

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California's water recovery: a record winter

California has faced multiple droughts in recent years, which have reduced its water supply and increased its water demand, as per Phys.org.

The state relies heavily on snowpack in the Sierra Nevada mountains as a natural reservoir that melts and feeds its rivers and aquifers throughout the year.

However, warmer temperatures and less precipitation have reduced the snowpack and increased evaporation.

The state has also experienced increased groundwater depletion due to pumping for irrigation and domestic use.

In 2022 to 2023, however, California received abundant rainfall and snowfall, thanks to a series of atmospheric rivers that brought moist air from the Pacific Ocean.

Atmospheric rivers are narrow bands of moisture that can transport large amounts of water vapor across long distances.

They can cause heavy precipitation and flooding when they encounter mountains or other barriers along the coast.

According to data from GRACE-FO, California saw its greatest year-over-year water gains in two decades between October 2022 and March, as per SpaceDaily.

The state gained about 500 millimeters (20 inches) of water equivalent in its Central Valley region, which is about twice as much as the average winter gain since 2002.

The maps showed the changes in water storage relative to the average from 2004 to 2010.

Blue colors indicate wetter than average conditions, while red colors indicate drier than average conditions.

The chart shows the month-to-month variations in water storage for the same region. The yellow line represents the GRACE-FO data, while the gray line represents the data from the original GRACE mission.

The chart shows that California's water storage reached its lowest point in October 2014, during a severe drought that lasted from 2012 to 2016.

It also shows that California's water storage reached its highest point in March, after a record-wet winter.

The GRACE-FO mission provides valuable information for monitoring and managing water resources on Earth.

It can help assess the availability and sustainability of water supply for various uses and needs.

It can also help evaluate the impacts and risks of water-related hazards, such as droughts, floods, and landslide, and can also help understand how water cycles interact with climate change and feedback.

The GRACE-FO data show that California's water situation has improved significantly after a wet winter, but it also shows that the state's water storage is still below its long-term average.

The state still faces challenges such as groundwater depletion, population growth, urbanization and environmental protection.

The state also needs to prepare for future variability and uncertainty in precipitation patterns due to climate change.

The GRACE-FO data also showed that California's water cycle is closely linked to the global climate system, as it is influenced by atmospheric and oceanic phenomena such as atmospheric rivers, El Niño and La Niña.

The state's water cycle also affects the global climate system, as it modulates the exchange of heat, moisture, and carbon between the land and the atmosphere.

The state's water cycle also affects the global carbon cycle, as it regulates the uptake and release of CO₂ by plants, soils and ecosystems.

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