For decades, our understanding of Earth's river systems lacked a crucial piece of the puzzle: a comprehensive picture of the volume of water they hold and how it fluctuates. A recent study led by NASA researchers and published in Nature Geoscience is revolutionizing this field. This groundbreaking research provides the first global accounting of Earth's rivers, offering invaluable insights for water resource management and furthering our understanding of the planet's water cycle.
The study sheds light on two key aspects: the total volume of water stored in rivers and how this volume changes over time. The researchers estimate that, on average, between 1980 and 2009, Earth's rivers held a total volume of 539 cubic miles (2,246 cubic kilometres). This seemingly vast amount is surprisingly, just around 0.006% of all freshwater on Earth. However, despite their relatively small proportion, rivers play a vital role in sustaining life and human civilizations.
Prior to this study, estimates of river volume were limited and lacked data on temporal variations. Traditionally, scientists relied on refinements of a single figure established in 1974 by the United Nations. This approach offered a static picture and lacked the granularity needed for effective water management strategies. Furthermore, limitations in data collection hampered past efforts. Observations, particularly for remote rivers, were scarce, and the uneven distribution of stream gauges, concentrated on larger rivers, introduced bias.
The NASA-led study breaks new ground by employing a novel methodology that combines real-world data with computer modelling. Researchers used stream-gauge measurements from approximately 1,000 locations around the world and incorporated them into computer models of millions of river segments. This innovative approach allowed them to correct simulated runoff data, resulting in a more comprehensive and accurate picture.
The ability to quantify river storage and discharge variations across the globe unlocks a treasure trove of insights for water resource management. The study identified regions experiencing intense human water use, including the Colorado River basin in the United States, the Amazon basin in South America, and the Orange River basin in southern Africa. In these regions, the study identified "negative discharge," indicating that less water exits a river segment than enters. This serves as a clear fingerprint of human water consumption, highlighting areas where water resource management strategies need to be carefully evaluated.
The study's consistent methodology allows for crucial comparisons between different regions. Water professionals can now analyze flow rates and human water use across diverse geographical areas, enabling them to make data-driven decisions for sustainable water management. This newfound ability to compare river systems empowers them to identify areas of potential strain and implement targeted solutions.
Looking ahead, the potential for further exploration is exciting. The recent launch of the Surface Water and Ocean Topography (SWOT) satellite opens new avenues for research. By mapping global water elevation, SWOT can provide valuable data to refine measurements of human impacts on the Earth's water cycle. This synergy between the NASA-led study and future satellite data has the potential to revolutionize our understanding of how humans interact with and influence our planet's vital river systems.
