For decades geoscientists have been trying to detect the influence of climate on the formation of rivers, but up to now there has been no systematic evidence.
24 September 2019
A new study, co-authored by researcher Dr Stuart Grieve, Lecturer in Physical Geography in Queen Mary University of London’s School of Geography, and published in the journal Nature, discovers a clear climatic signature on rivers globally that challenges existing theories.
Up until now scientists have lacked a large, systematic dataset of rivers that spans the range of climate zones on Earth, enabling full exploration of the links between climate and river form. The research team produced a new, freely available, database of river long profiles, generated from data originally collected by NASA’s space shuttle. The University of Bristol-led research included specialist software developed by the team to establish a new long profile database that includes over 330,000 rivers across the globe.
Dr Grieve said: “Combining satellite data with high performance computing is revolutionizing our discipline; allowing us to understand how our planet is changing at unprecedented scales.
“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.”
The new research shows that while river long profiles tend to be concave up in humid regions, they become progressively straighter in drier regions. The study shows for the first time at the global scale that there are distinct differences in river long profile shapes across climate zones, and that the reason behind these differences lies in the expression of aridity in streamflow in rivers.
In humid regions, rivers tend to have flow in them all year round which continually moves sediment and erodes the overall profile into a concave up shape. As the climate becomes progressively arid (from semi-arid, to arid, to hyper-arid), rivers only flow a few times per year when it rains, moving sediment infrequently. Additionally, arid rivers tend to experience brief, intense rainstorms, which do not create flow over the entire river length.
These links between climate, streamflow and long profile shape are explained in the paper using a numerical model which simulates the evolution of river profiles over time in response to streamflow characteristics.
The authors show that regardless of all other potential controls on river profiles, streamflow characteristics have a dominant effect on the final profile shape. They demonstrate that the differences in the climatic expression of streamflow explain the variations in profile shape across climatic regions in their database.
Dr Katerina Michaelides, from Bristol’s School of Geographical Sciences, who led the research added: “Traditional theory included in textbooks for decades describes that river long profiles evolve to be concave up. Existing theories are biased towards observations made in humid rivers, which are far better studied and more represented in published research than dryland rivers.
“Our study shows that many river profiles around the world are not concave up and that straighter profiles tend to be more common in arid environments.”
“I think dryland rivers have been understudied and under-appreciated, especially given that drylands cover 40 per cent of the global land surface. Their streamflow expression gives unique insights into the climatic influence on land surface topography.”
Read the paper here: https://www.nature.com/articles/s41586-019-1558-8.pdf
Study Geography at Queen Mary University of London
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