Thursday, 11 March 2021
An international research team has demonstrated for the first time that climate change caused by humans is responsible for changes in river flow worldwide.
The University of Nottingham is part of a team of experts from 12 countries led by ETH Zurich that have had their findings published in the scientific journal Science.
The team set about investigating extreme river flow trends which began in the 1970s, in which they observed some regions, such as the Mediterranean and north-eastern Brazil becoming drier, while other regions have seen more water in their rivers, such as in Scandinavia.
Until now, it was unclear whether these trends were natural, caused by water management practices or by human-induced climate change.
After analysing data from 7,250 measuring stations worldwide, along with a set of hydrological model simulations of global river flows, scientists were able to demonstrate that river flow changed systematically between 1971 and 2010.
To understand the cause of these changes, the researchers carried out several computer simulations, using global hydrological models fed with observed climate data from the period studied (1971 to 2010). The results of the model calculations closely matched the analysis of observed river flow.
Simon Gosling, Professor of Climate Risk at the University of Nottingham, with Dr Hannes Müller Schmied of Goethe-University Frankfurt, led the coordination of the hydrological model simulations used in the study.
The same models were used earlier this year to show that the number of people suffering extreme droughts across the world will double in less than 80 years as a result of changes in climate and population.
When we compared the 7,000 or so river records with simulations of river flows from hydrological models that were run once with human-made greenhouse gases and once without, we found that the models could only replicate the real-world data when we included the human-made greenhouse gases in the picture. This tells us it is highly likely that trends in extreme river flows across the world are due to human-induced climate change.
Professor Gosling added: “We were able to rule out water management as the culprit, by using a similar approach, where we compared model simulations with and without human water management respectively. So long as human-made greenhouse gases were included, we found that the inclusion or exclusion of water management had little effect on past river flows. This told us that something else had to be driving recent trends in extreme river flows - which was human-induced climate change.”
The study is the first to use direct observations to demonstrate that climate change has a globally visible influence on rivers.
Lukas Gudmundsson, lead author of the study at ETH Zurich, said “This was only possible thanks to the great collaboration between researchers and institutions from 12 countries.”
Data used in the study represents the largest global data set of river flow observations available today. “Thanks to this data, we were able to validate the models and demonstrate that they provide a good reflection of reality” says Gudmundsson.
This means that the models can also provide reliable scenarios on how rivers will continue to change in the future. Such projections provide an important basis for planning in the affected regions in order to secure water supply and adjust to climate change.
Professor Gosling added: “The changes in river flows that we attribute to human-induced climate change have important implications for flood risk management, water scarcity, and the functioning of ecosystems in the near future.”
The changes in river flows that we attribute to human-induced climate change have important implications for flood risk management, water scarcity, and the functioning of ecosystems in the near future.
Story credits
More information is available from Professor Simon Gosling in the Faculty of Social Sciences at the University of Nottingham at Simon.Gosling@nottingham.ac.uk; or Katie Andrews, in the Press Office at the University of Nottingham at Katie.Andrews@nottingham.ac.uk
Notes to editors:
About the University of Nottingham
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