global freshwater levels decline NASA satellite discovery

Global Freshwater Levels Plummet, NASA Satellite Data Shows

Introduction

Observations from NASA-German satellites led an international research team to discover a sharp decline in Earth's total freshwater reserves beginning in May 2014, with levels remaining consistently low. Published in Surveys in Geophysics, the findings suggest Earth's continents may now be in a sustained dry phase.

Key Findings from NASA-German Satellite Data

Decline in Freshwater Reserves (2015-2023)

Between 2015 and 2023, satellite data revealed that Earth's terrestrial freshwater storage, encompassing surface water and underground aquifers, averaged 290 cubic miles (1,2000 cubic km) less than the 2002-2014 average. "This is equivalent to losing two and a half times the volume of Lake Erie," noted Mattew Rodell, a hydrologist at NASA's Goddard Space Flight Center.

Impact of Drought and Agriculture

Periods of drought, coupled with the growing expansion of irrigated agriculture, force farms and cities to increasingly depend on groundwater, creating a feedback loop of diminishing underground reserves. With reduced rainfall and snowmelt, these freshwater sources are not replenished, prompting even greater groundwater extraction.

Global Water Stress and Implications

UN Report on Water Scarcity

A 2024 UN report on water stress highlights that diminishing water availability burdens farmers and communities, potentially triggering famine, poverty, conflicts, and heightened disease risks from contaminated water sources.

The Role of GRACE Satellites in Tracking Freshwater Decline

The Role of GRACE Satellites

Researchers pinpointed this sudden global freshwater decline through data from the Gravity Recovery and Climate Experiment (GRACE) satellites, a collaborative effort by NASA, the German Aerospace Center, and the German Research Centre for Geosciences. GRACE detects monthly gravity variations to rack changes in terrestrial water mass. The original GRACE mission operated from March 2002 to October 2017, with its successor, GRACE-Follow On (GRACE-FO), launching in May 2018.

Drought Events and Global Impact

The study reveals that the global freshwater decline was initiated by a severe drought in northern and central Brazil, followed by widespread droughts across Australasia, South America, North America, Europe, and Africa. Elevated tropical Pacific ocean temperatures from late 2014 to 2016, culminating in a significant El Niño event, disrupted atmospheric jet streams, reshaping global weather and rainfall patterns.

Persistent Freshwater Losses and the Role of Climate Change

Global Warming's Contribution

Despite the conclusion of the El Niño event, global freshwater levels did not recover. Rodell and his team note that 13 of the 30 most severe droughts observed by GRACE have occurred since January 2015. The researchers suggest that persistent freshwater losses may be linked to global warming.

Climate Change and Extreme Precipitation

Global warming increases the atmosphere's capacity to hold water vapor, intensifying precipitation events, explains NASA Goddard meteorologist Michael Bosilovich. Although annual rainfall and snowfall totals may remain relatively stable, prolonged intervals between heavy precipitation allow soil to dry and compact, reducing its capacity to absorb water during subsequent rains.

"Extreme precipitation presents a challenge," explained Bosilovich, "as water tends to run off rather than infiltrate the soil to replenish groundwater reserves." Since the 2014-2016 El Niño, global freshwater levels have remained persistently low, with a larger portion of water now retained in the atmosphere as vapor.

Rising temperatures enhance both the evaporation of water from the surface into the atmosphere and the atmosphere's capacity to hold moisture, leading to more frequent and intense droughts.

Although there are indications that the sudden decline in freshwater may be primarily driven by global warming, establishing a definitive connection between the two remains challenging, according to Susanna Werth, a hydrologist and remote sensing scientist at Virginia Tech, who was not involved in the study.

"Climate predictions carry inherent uncertainties," Werth explained. "Both measurements and models are subject to errors."

Will Freshwater Levels Recover?

It is still uncertain whether global freshwater will recover to pre-2015 levels, stabilize, or continue to decrease. Given that the nine warmest years on record align with the sharp drop in freshwater, Rodell stated, "We don't believe this is a coincidence, and it may signal what's to come."

Source

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