Scientists have found that volcanic eruptions affect the flow of the world’s major rivers.

New research from the University of Edinburgh shows that aerosol particles ejected into the air following volcanic eruptions don’t just contaminate the atmosphere, they can often trigger rainfall shortages that ultimately affect river systems worldwide.

In the first study of its kind, University of Edinburgh scientists Carley Iles and Gabriele Hegerl compared annual water flow in 50 rivers around the world with the timing of major volcanic eruptions, notably Agug in 1963, El Chichon in 1982 and Pinatubo in 1991.

For some rivers, records went back into the 19th century, making it possible to take into account earlier eruptions too.

They discovered that a year or two after these volcanoes hurled massive amounts of debris into the upper atmosphere they created a partial sunscreen and the flows of tropical rivers decreased.

On the contrary, river flow increased in some regions, including the U.S. southwest and parts of South America. Researchers linked this to the disruption of atmospheric circulation patterns.

Dr. Carley Iles, from the School of GeoSciences at the University of Edinburgh, said in a statement. “Our findings reveal the indirect effect that volcanoes can have on rivers, and could be very valuable in the event of a major volcanic eruption in future,”

The study, published in Nature Geoscience, cautioned against so-called geo-engineering schemes that have been proposed as an answer for cooling down an overheated planet or global warming.

“As well as affecting river flow and rainfall, volcanic eruptions have a cooling effect on climate,” Dr Iles said.

“All of these impacts come about because volcanoes inject particles — sulfate aerosols — high up into the atmosphere, and these spread out and reflect sunlight back out into space.”