Nearly half of the world’s largest rivers have experienced reduced water flow. On the other hand, small upstream rivers are seeing an increase in flow. These changes hold serious implications for flooding, ecosystems, hydropower, and freshwater availability, says a groundbreaking study.
University of Massachusetts Amherst and University of Cincinnati researchers studied river flow changes globally. They mapped these changes over the past 35 years. Dongmei Feng is the study’s lead author. She is also an assistant professor at the University of Cincinnati. She emphasizes that this research is the first to analyze river flow on a global scale. Previous studies focused on specific river parts, but Feng’s approach takes a broader view of the entire river system. “Rivers are not isolated,” she says. “We must consider both upstream and downstream factors when analyzing river changes.”
RIVER FLOW AND ITS GLOBAL IMPACT
River flow, also known as discharge, is crucial for sustaining ecosystems and human life. It describes the amount of water flowing through a river, measured in cubic meters per second. Typically, flow rates are determined using tools like acoustic Doppler current profilers. Nonetheless, these methods only measure specific locations and provide limited data.
“There are only about 10,000-15,000 places around the world where we know the river discharge,” says Colin Gleason, a co-author of the study.
Feng and Gleason’s team developed a new method using satellite data. They used computer modeling to allow the study of river flow rates. This covers 3 million stream reaches globally. This covers rivers every day over 35 years, providing new insights into changes in river flow patterns.
DECREASING FLOW IN DOWNSTREAM RIVERS
The study found that 44% of the world’s largest downstream rivers experienced a decrease in flow. This results in lower water availability for drinking and irrigation in many regions. Gleason points out, “If river flow is dropping, communities struggle to meet their water needs, especially as populations grow.”
Additionally, a decrease in flow means rivers have less power to move sediment. This impacts deltas, which rely on sediment transport to counter sea-level rise. Modern damming practices further reduce sediment movement, exacerbating the issue.
RISING FLOW IN SMALL, UPSTREAM RIVERS
Contrasting with the downstream rivers, 17% of the world’s smallest rivers saw an increase in flow. This trend is particularly noticeable in mountainous areas. Though this helps ecosystems in the short term, it brings challenges for nearby communities. The researchers observed a 42% increase in large floods along these rivers.
Feng notes that while floods are harmful to humans, they can help species that rely on seasonal flooding. For instance, more frequent floods in the western Amazon have led to increased fish migration, which helps local ecosystems.
HYDROPOWER IMPLICATIONS IN UPSTREAM REGIONS
Smaller, upstream rivers experiencing increased flow could also interfere with hydropower development. In regions like High Mountain Asia, countries such as Nepal and Bhutan are exploring clean energy sources. However, increased river flow could worsen erosion. “The increased flow means more sediment is transported downstream, which could clog hydropower plants,” says Feng.
CAUSES OF RIVER FLOW CHANGES
While the study does not pinpoint exact causes, researchers attribute the changes to climate change and human activity. Climate change increases precipitation in some areas, while in mountainous regions, snowmelt has intensified due to rising temperatures. Human activities like water extraction for agriculture and wastewater dumping also play a role in altering river flow patterns.
UNDERSTANDING AND ADDRESSING THE ISSUE
The study’s findings highlight the importance of understanding river flow changes. This understanding is crucial to better manage water resources. It also helps us plan for the future. “We need more data to make informed decisions,” says Gleason. This study provides crucial insights that can help policymakers and communities adapt to the shifting dynamics of river systems.
The researchers map river flow on a global scale. They provide the data needed for more informed decisions about water management. This information also aids in infrastructure development and climate adaptation strategies. As Gleason explains, “If we understand these changes, we can take the necessary steps to mitigate their impact.”
