From ETH Zürich[Eidgenössische Technische Hochschule Zürich](CH): “Climate change influences river flow”

From ETH Zürich[Eidgenössische Technische Hochschule Zürich](CH)

11.03.2021
Claudia Hoffmann

River flow has changed significantly worldwide in recent decades. An international research team led by ETH Zürich has now demonstrated that it is climate change, rather than water and land management, that plays a crucial role at a global level.

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Rivers and streams are changing on a global scale due to climate change. The image shows a river landscape in Poland. Credit: Shalith / iStock.

Climate change is affecting the water balance of our planet: depending on the region and the time of year, this can influence the amount of water in rivers potentially resulting in more flooding or drought. River flow is an important indicator of water resources available to humans and the environment. The amount of available water also depends on further factors, such as direct interventions in the water cycle or land use change: if, for example, water is diverted for irrigation or regulated via reservoirs, or forests are cleared and monocultures grown in their place, this can have an impact on river flow.

However, how river flow has changed worldwide in recent years was so far not investigated using direct observations. Similarly, the question whether globally visible changes are attributable to climate change or to water and land management had not been clarified.

Now, an international research team led by ETH Zürich has succeeded in breaking down the influence of these factors, after analysing data from 7,250 measuring stations worldwide. The study, which has been published in the renowned scientific journal Science, demonstrates that river flow changed systematically between 1971 and 2010. Complex patterns were revealed – some regions such as the Mediterranean and north-​eastern Brazil had become drier, while elsewhere the volume of water had increased, such as in Scandinavia.

The quest for the causes

“The actual question, however, concerned the cause of this change,” says Lukas Gudmundsson, lead author of the study and senior assistant in the group led by Sonia Seneviratne, professor at the Institute for Atmospheric and Climate Science at ETH Zürich.

To answer this question, 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. “This means that climatic conditions can explain the observed trends in the flow volumes,” says Gudmundsson. In a second procedure, the researchers included additional water and land management in their simulations in order to study the influence of these factors. This did not affect the result, however. “Changes in water and land management are evidently not the cause of global changes in rivers,” he says.

Although water management and land use can result in large local fluctuations in flow volumes, investigating this was not within the scope of the study, adds Gudmundsson: “For us, it was not about local trends but global changes that become visible over longer periods.” This is why the researchers did not consider data from individual measuring stations in isolation, but collated them into larger subcontinental regions for the analysis, thereby making it possible to identify the influence of climate change.

The impact of greenhouse gases

The researchers were able to substantiate the role of climate change using the detection and attribution method. For this they compared the observations with simulations from climate models that were calculated once with man-​made greenhouse gases and once without. In the first case the simulation matched the actual data, but in the second case it did not. “This suggests that the observed changes are highly unlikely without climate change,” says Gudmundsson.

The study is the first to use direct observations to demonstrate that climate change has a globally visible influence on rivers. “This was only possible thanks to the great collaboration between researchers and institutions from 12 countries,” emphasises Gudmundsson. The data collection from the 7,250 measuring stations worldwide was also the result of a joint effort: researchers had collated the data with Australian collaboration partners in a previous study. This data now represents the largest global data set with 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 future. Such projections provide an important basis for planning in the affected regions in order to secure water supply and adjust to climate change.

See the full article here .

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ETH Zurich campus
ETH Zürich [Eidgenössische Technische Hochschule Zürich] (CH) is a public research university in the city of Zürich, Switzerland. Founded by the Swiss Federal Government in 1854 with the stated mission to educate engineers and scientists, the school focuses exclusively on science, technology, engineering and mathematics. Like its sister institution EPFL[École polytechnique fédérale de Lausanne](CH), it is part of the Swiss Federal Institutes of Technology Domain (ETH Domain), part of the Swiss Federal Department of Economic Affairs, Education and Research.

The university is an attractive destination for international students thanks to low tuition fees of 809 CHF per semester, PhD and graduate salaries that are amongst the world’s highest, and a world-class reputation in academia and industry. There are currently 22,200 students from over 120 countries, of which 4,180 are pursuing doctoral degrees. In the 2021 edition of the QS World University Rankings ETH Zürich is ranked 6th in the world and 8th by the Times Higher Education World Rankings 2020. In the 2020 QS World University Rankings by subject it is ranked 4th in the world for engineering and technology (2nd in Europe) and 1st for earth & marine science.

As of November 2019, 21 Nobel laureates, 2 Fields Medalists, 2 Pritzker Prize winners, and 1 Turing Award winner have been affiliated with the Institute, including Albert Einstein. Other notable alumni include John von Neumann and Santiago Calatrava. It is a founding member of the IDEA League and the International Alliance of Research Universities (IARU) and a member of the CESAER network.

ETH Zürich was founded on 7 February 1854 by the Swiss Confederation and began giving its first lectures on 16 October 1855 as a polytechnic institute (eidgenössische polytechnische Schule) at various sites throughout the city of Zurich. It was initially composed of six faculties: architecture, civil engineering, mechanical engineering, chemistry, forestry, and an integrated department for the fields of mathematics, natural sciences, literature, and social and political sciences.

It is locally still known as Polytechnikum, or simply as Poly, derived from the original name eidgenössische polytechnische Schule, which translates to “federal polytechnic school”.

ETH Zürich is a federal institute (i.e., under direct administration by the Swiss government), whereas the University of Zürich is a cantonal institution. The decision for a new federal university was heavily disputed at the time; the liberals pressed for a “federal university”, while the conservative forces wanted all universities to remain under cantonal control, worried that the liberals would gain more political power than they already had. In the beginning, both universities were co-located in the buildings of the University of Zürich.

From 1905 to 1908, under the presidency of Jérôme Franel, the course program of ETH Zürich was restructured to that of a real university and ETH Zürich was granted the right to award doctorates. In 1909 the first doctorates were awarded. In 1911, it was given its current name, Eidgenössische Technische Hochschule. In 1924, another reorganization structured the university in 12 departments. However, it now has 16 departments.

ETH Zürich, EPFL (Swiss Federal Institute of Technology in Lausanne) [École polytechnique fédérale de Lausanne](CH), and four associated research institutes form the “ETH Domain” with the aim of collaborating on scientific projects.

Reputation and ranking

ETH Zürich is ranked among the top universities in the world. Typically, popular rankings place the institution as the best university in continental Europe and ETH Zürich is consistently ranked among the top 1-5 universities in Europe, and among the top 3-10 best universities of the world.

Historically, ETH Zürich has achieved its reputation particularly in the fields of chemistry, mathematics and physics. There are 32 Nobel laureates who are associated with ETH Zürich, the most recent of whom is Richard F. Heck, awarded the Nobel Prize in chemistry in 2010. Albert Einstein is perhaps its most famous alumnus.

In 2018, the QS World University Rankings placed ETH Zürich at 7th overall in the world. In 2015, ETH Zürich was ranked 5th in the world in Engineering, Science and Technology, just behind the Massachusetts Institute of Technology(US), Stanford University(US) and University of Cambridge(UK). In 2015, ETH Zürich also ranked 6th in the world in Natural Sciences, and in 2016 ranked 1st in the world for Earth & Marine Sciences for the second consecutive year.

In 2016, Times Higher Education World University Rankings ranked ETH Zürich 9th overall in the world and 8th in the world in the field of Engineering & Technology, just behind the Massachusetts Institute of Technology(US), Stanford University(US), California Institute of Technology(US), Princeton University(US), University of Cambridge(UK), Imperial College London(UK) and