Expert comment: UK floods from Storm Christoph caused by ‘atmospheric river’
Release Date 21 January 2021
Helen Griffith, a research scientist studying atmospheric rivers at the University of Reading, said:
"Our early analysis suggests that we can blame a particularly large atmospheric river for the heavy, persistent rain that came with Storm Christoph. In a sense, it is not surprising that many rivers on the ground are now reaching record levels, as some atmospheric rivers have been found to carry as much water as the Amazon or the Nile.
"Atmospheric rivers are narrow regions of air that transport water through the lower atmosphere in long, narrow bands. Scientists have been aware of them for a while in the US, but we are only just beginning to be able to observe and predict them properly in Europe. In the UK, these intensely wet regions of air are often associated with winter storms from the Atlantic, such as Storm Desmond in December 2015, and Ciara and Dennis in February 2020. When atmospheric rivers hit land, the low-lying wet air is pushed up over the coast, leading to heavy rain that goes on and on.
"We are currently conducting research at the University of Reading and European Centre for Medium-range Weather Forecasts (ECMWF) to understand more about atmospheric rivers to improve operational flood forecasts. While we knew Storm Christoph was coming, we didn't know exactly where it would strike and dump its water, so we need to understand more about how and where atmospheric rivers interact with the land surface. We published a scientific paper outlining this work in 2020.
"At the moment, the UK usually gets three or four atmospheric rivers each winter, although not all lead to the impacts on the scale of Storm Christoph. However, atmospheric rivers are predicted to get bigger, and more frequent, as a result of a warming climate. Linking climate change to flooding is often difficult, but atmospheric rivers are one of those phenomena where the fingerprints of human activity may be all too evident. We will need to prepare for more floods like these in the future."