Flood predictions, traditionally reliant on local historical data, are undergoing a paradigm shift. A research project led by TU Wien (Vienna) has identified a method to vastly improve flood forecasts by incorporating international data from hydrologically analogous regions. This approach offers a novel perspective on predicting catastrophic “mega-floods.”
Traditionally, flood risk assessment has been based on the worst historical flood events within a specific region. This is considered the realistic upper limit for future floods.
However, recent occurrences of mega-floods have upended this assumption. These extreme events, often outliers based on local data, have repeatedly taken communities by surprise.
“Predicting the extent of such mega-floods is very difficult,” said Professor Günter Blöschl, who led the project. He noted that conventional methods focus on extrapolating probabilities from past regional floods.
However, the researchers have developed a much better strategy. They analyzed data from more than 8,000 gauging stations across Europe, from the years 1810 to 2021.
This comprehensive data set revealed a crucial insight: mega-floods that appear as anomalies locally are often within the expected range when considering similar hydrological conditions across the continent.
“The decisive step was to anticipate mega-floods in one place by using data from similar river basins in other places on the continent,” explained study lead author Dr. Miriam Bertola. “In each river basin we can learn from other areas that have similar climatic and hydrological characteristics where mega-floods may have already occurred.”
The 2021 flood disaster in Germany and Belgium, which tragically claimed over 220 lives, serves as a relevant case study. This event, which was unexpected based on regional data, would have been anticipated using the new continental-scale approach.
Such events are no longer statistical outliers when viewed in the broader context of similar river basins across Europe.
“It is important to consider not only geographically adjacent areas, but also areas with similar conditions – these may also be located further away,” said Professor Blöschl.
“It is therefore essential to move beyond national flood-risk assessment and share information on mega-floods across countries and continents, to reduce the surprise factor of their occurrence and save lives.”
Mega-floods, or paleofloods, represent colossal hydrological events with water flow rates surpassing those recorded in human history. They are not recent phenomena but have occurred throughout the Earth’s geological past.
These floods are identified and studied through the sediments they deposit and the landforms they shape or erode.
Unlike regular floods primarily caused by meteorological events like heavy rain or rapid snowmelt, mega-floods often result from the sudden release of large water volumes due to specific geological or hydrological triggers.
In geomorphology, mega-floods are sometimes referred to as outburst floods, characterized by their high magnitude and low frequency. They are catastrophic events involving the abrupt discharge of vast quantities of water.
Throughout the Earth’s history, such floods have been caused by various mechanisms, including the collapse of ice sheets or glaciers that formed dams for proglacial lakes, landslides blocking rivers and forming lakes, or volcanic activities creating dams that eventually fail.
These events have been known to occur not only on Earth but are also inferred from geomorphological evidence on Mars.
The study is published in the journal Nature Geoscience.
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.