What amount of water do Earth's rivers hold?

Rivers serve as vital lifelines across the planet, sustaining ecosystems, human populations, and economic activity. Understanding their dynamics, including the amount of water that is stored and discharged by rivers, is essential for effective freshwater resource management.

A recent NASA-led study provides novel insights into these dynamics, highlighting regions experiencing significant water stress.

River water storage amount

Historically, obtaining accurate and reliable estimates of the total volume of water stored in rivers worldwide has posed significant challenges due to limitations in measurement techniques and data availability.

The recent research conducted by NASA has made significant strides in addressing this issue. By employing a combination of advanced computational models and extensive stream-gauge measurements, the study estimates that Earth’s rivers collectively hold about 539 cubic miles (2,246 cubic kilometers) of water.

The volume of water in rivers, although small, is significantly important. It represents a fraction of the total freshwater resources, which are only 2.5% of Earth’s water. Yet, this amount is essential for management of the global water cycle.

River water supports ecosystems, agriculture, and human populations extensively. Its impact is much greater than its volume implies. This knowledge is crucial for those managing water resources.

Millions of river segment simulations

The research team integrated traditional stream-gauge measurements with advanced hydrological computer simulations. This method involved analyzing approximately 3 million river segments across the globe, representing a comprehensive effort to map river dynamics more accurately than ever before.

The researchers observed important discrepancies between the runoff simulated by their hydrological models and the actual data from stream gauges. These differences highlighted the need for adjustments in their computational models to more accurately mirror real-world conditions. By addressing and reconciling these discrepancies, the researchers refined their models to improve calculations of river water volumes.

The ability to calculate both storage and discharge with greater precision is vital for understanding the balance of water within river systems, assessing the sustainability of water use, and planning for future water management strategies under changing climatic conditions.

This innovative blend of empirical measurement and simulation represents a major step forward in hydrological science, providing a clearer picture of riverine water dynamics that are essential for both science and policy-making.

Amazon’s river water storage amount

The Amazon River basin has been highlighted as a particularly significant area in the recent study, demonstrating its substantial role within the global hydrological system.

This vast basin, which is the largest river system in the world by volume, was found to contain approximately 38% of the world’s total river water storage. This significant figure not only illustrates the sheer volume of water that the Amazon holds but also emphasizes its crucial role in maintaining global water balance.

Furthermore, the study found that the Amazon basin accounts for 18% of the total river discharge into the world’s oceans. This high percentage of discharge reflects the Amazon’s pivotal function in transporting freshwater from land to sea, influencing oceanic salinity, currents, and ultimately global climate patterns.

Areas of water stress

“These are locations where we’re seeing fingerprints of water management,” said lead author Elyssa Collins, who conducted the analysis as a JPL intern and doctoral student at North Carolina State University in Raleigh.

The study pinpoints regions where intensive human water use results in reduced river discharge. Notable areas include the Colorado, Amazon, Orange, and Murray-Darling river basins. This analysis identifies potential hotspots where careful water resource management is paramount.

“We don’t know how much water is in the account, and population growth and climate change are further complicating matters,” said JPL’s Cédric David, a co-author of the study. “There are many things we can do to manage how we’re using it and make sure there is enough water for everyone, but the first question is: How much water is there? That’s fundamental to everything else.”

Remote sensing for river monitoring

The recent launch of NASA’s Surface Water and Ocean Topography (SWOT) satellite offers valuable new data for water resource monitoring. SWOT’s ability to map global surface water elevations, including river heights, complements the findings of this study, enhancing potential for refined analysis and informed management decisions.

This comprehensive study advances our understanding of river water dynamics and pinpoints regions facing increasing amounts of water scarcity. These insights emphasize the need for proactive freshwater resource management strategies to ensure the continued health of these vital systems and the communities they sustain.

The study is published in the journal Nature Geoscience.

Image Credit: NASA

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