Rivers are vital for wildlife and people's livelihoods, but they are threatened by climate change and extreme weather.

A new study looking at the Corinth Rift, a semi-arid area in Greece, suggests that Mediterranean rivers can become ‘supercharged’ in response to shifting weather patterns caused by climate change.

During heavy rainfall, these rivers carry large amounts of mud, rocks and sediment, increasing the risk of floods and damage to landscapes in the region.

With changing rainfall patterns due to climate change, however, the researchers suggest that the amount of sediment being pushed through Mediterranean rivers could potentially double by the year 2100 – with important implications for ecosystems, agriculture, and infrastructure.

The study, led by researchers in the Department of Earth Science and Engineering at Imperial College London, is published in the journal Geology.

‘Ephemeral’ rivers

The Corinth Rift is home to ‘ephemeral’ or ‘intermittent’ rivers – a type of river that flows irregularly and is often found in arid or semi-arid regions like the Mediterranean.

Lead author Jonah McLeod, of Imperial’s Department of Earth Science and Engineering, explains:

“Our study looks at how rivers flow ‘intermittently’ – remaining dry for long periods of time and only flowing rarely, which affects how much sediment they carry. During extreme storms, these intermittent rivers carry years’ worth of mud, sand and rocks downstream, supercharged by heavy rainfall.”

Even though the rivers might not flow very often, when they become ‘supercharged’ during extreme storms and displace a lot of sediment, they can lead to flooding and erosion – damaging homes and harming natural habitats.

Understanding the changing flow of rivers

To understand what climate change could do to rivers in this region, researchers sought to find out how often riverbeds get stirred up.

By combining calculations on sediment built up over thousands of years in the Corinth Rift with information about past floods and rainfall, they found that extreme storms in the Mediterranean have occurred about once every four years – when rainfall reaches more than 50 millimetres in a day.

However, as the climate changes, researchers expect to see a 20% increase in extreme rainfall in Greece by 2100, leading to rivers becoming ‘supercharged’ by a 100% increase in sediment being moved each year.

“There is a threshold for the amount of rainfall it takes to move large amounts of sediment. Below this threshold, barely any sediment will move. Over it, loads will. Our calculations suggest that the expected 20% increase in extreme rainfall would cause this threshold to be surpassed twice as often – doubling the amount of sediment moved by these rivers by the end of the century,” said Jonah McLeod.

Planning for extreme storms

As time goes on and climate change worsens, researchers warn that more extreme storms and river intermittency could impact landscapes across Mediterranean countries like Greece, Spain and France.

As a consequence, we are likely to see rivers carrying and moving more sediment than we are used to – potentially causing flooding and erosion, and damaging homes and landscapes in the process.

“Understanding how climate change is affecting rivers can help us prepare for and prevent hazards like erosion and flooding,” explains co-author Dr Alexander Whittaker, Reader in Landscape Dynamics at the Department of Earth Science and Engineering.

“This knowledge can help policymakers better plan for hazards and natural disasters – for example by putting in place emergency response plans or land use planning and development policies to prevent and mitigate damage from all this extra sediment carried by Mediterranean rivers during extreme storms.”