How is the shape of global rivers changing?!
River flows move upstream due to climate change and human activities. A study of how the hydrosphere has transformed over the past 35 years, which analyzed the flow of almost 3 million rivers worldwide, finds that the outlets of large rivers are affected by a significant decrease in water flow, while the headwaters of rivers small ones. are experiencing a significant increase in flow. The research from the University of Massachusetts Amherst and the University of Cincinnati (United States) was published in Science.
Previous works to know the flow rate of rivers ie. the volume of water passing through a certain section of the river in a unit of time, had considered only specific stretches of water flows, studied using manual instruments that measure direction and intensity. of currents in the water column.
"But as we know, rivers are not isolated. So if we are interested in a location, we need to think about how it affects upstream and downstream. Think of the river system as a whole and organically connected system," explains Colin Gleason, associate professor of Civil and Environmental Engineering at the University of Massachusetts and author of the study.
With previous measurements we had analyzed "about 10-15 thousand tiny infinitesimal slices of rivers in the world whose flow rates we knew, over millions upon millions of km of rivers," adds Gleason. To correct this, together with his colleague Dongmei Feng from the University of Cincinnati, the scientist used satellite surveys and computational models to study how the flow of 2.9 million rivers around the world had changed every day over the past 35 years. Finding which waterways were transforming most often, with changes in flow rate of 5-10% per year, and at what rate.
Rivers react differently to factors such as climate change and human activities. 44% of the largest downstream river outlets saw an annual decline in their water flow in the period considered; in contrast, 17% of smaller sources in upstream rivers had an annual increase in water level. These changes have had a significant impact on the relationship between people and rivers.
Less water downstream means less water resources for irrigation and domestic use, and less river energy to spread sediments in their deltas, an important process to counteract sea-level rise. More water upstream means increased risk of flooding of small mountain rivers, an event which, in some controlled contexts, may also be beneficial, due to increased nutrient and species transport. of migratory fish.
But increased upstream flow can also favor erosion processes, moving sediments that can clog dams at hydroelectric plants, a problem to consider in renewable energy development plans. There are probably two factors at the origin of these changes: increased precipitation and high-elevation snowmelt, which increase river flow upstream; and withdrawing water from rivers for agricultural or domestic use, which affects downstream.
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