Climate signature detected in Earth's rivers

Scientists have found a climate signature in the planet's rivers.

Climate dictates many of Earth's geologic and hydrological systems, but scientists have struggled to pinpoint the influence of climate on the formation of rivers. Now, researchers have uncovered evidence suggesting climate controls the elevational profile of rivers across the globe.

An elevational profile, or long profile, is formed by tracing a river from its headwaters to its mouth. Most rivers fall steeply from the uplands before flattening in the lowlands. The pattern produces a concave up shape. Less common is a straight long profile, which if formed by a river that descends evenly in elevation, like a ramp from mountain to sea.

The latest analysis suggests the long profiles of rivers in humid regions are more likely to be concave up, while the long profiles of rivers in drier regions are more likely to straighten.

"The long profile is formed gradually over tens of thousands to millions of years, so it tells a bigger story about the climate history of region," Shiuan-An Chen, researcher at the University of Bristol, said in a news release. "We would expect climate to affect the river long profile because it controls how much water flows in rivers and the associated force of water to move sediment along the riverbed."

Until now, river profile data has been incomplete and decentralized. Using data collected by NASA's space shuttle program, researchers at Bristol and Queen Mary University compiled a long profile database of more than 330,000 rivers spanning a variety of the planet's climate zones.

The comprehensive database allowed scientists, for the first time, to identify patterns among the long profile shapes found in different climate zones. Because rivers in humid regions tend to experience steady flows year-round, they continually move sediment, which yields a concave up shape.

Rivers in semi-arid and arid regions get progressively straighter -- the greater the aridity, the straighter the long profile.

These patterns allowed scientists to build a numerical model simulating evolution of river profiles across millennia in response to different streamflow characteristics.

"Traditional theory included in textbooks for decades describes that river long profiles evolve to be concave up," said Bristol geoscientist Katerina Michaelides. "Existing theories are biased towards observations made in humid rivers, which are far better studied and more represented in published research than dryland rivers."

Though drylands account for 40 percent of global land surface, the authors of the latest study -- published this week in the journal Nature -- suggest dryland rivers are understudied. The authors hope the newly compiled database will help change that.

"Combining satellite data with high performance computing is revolutionizing our discipline; allowing us to understand how our planet is changing at unprecedented scales," said Stuart Grieve from Queen Mary University of London. "Our analysis of these data only scratches the surface of the potential that this fusion of data, computer power and geoscientific insight can offer us to understand our planet, as well as others in the solar system."

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