Guardian ‘Floods in 2009 and 2015 were worst in Cumbria for centuries – study’

Analysis in north-west England linked to evidence of UK’s vulnerability to climate crisis

The floods of 2009 and 2015 in north-west England were the worst for more than 550 years, according to groundbreaking analysis of lake sediment in the region. Residents have long suspected that the devastating floods were the worst in living memory, but this confirmation – from an analysis of lake sediment layers – provides a unique window on to the history of flooding in one of the wettest parts of England, and reveals the global climate crisis.

Floods in the region in 2009 and 2015 – the latter the result of Storm Desmond – grabbed the headlines at the time, but are increasingly being linked to evidence of the UK’s vulnerability to the climate emergency. The new analysis shows that the most recent floods were unprecedented in key respects. In 2015, more than 50,000 homes in Cumbria were flooded or had severe impacts from flooding. While the loss of life was relatively small, the damage to local people is still being felt in many areas. Similarly, floods in 2009 left thousands of people displaced from their homes, which took years to be resolved.

Richard Chiverrell, a professor of physical geography at the University of Liverpool, and the lead scientist conducting the research, said: “The convergence of information suggests a link with a warmer world and recent extreme flooding is likely.”

He said factors such as the way land is managed and changing farming practices were likely to have only a small effect, compared with the overriding force of changing weather.

He added: “The unprecedented nature of the recent phase of extreme floods accords with statements from the Environment Agency that climate changes and associated impacts on the frequency and magnitude of extreme events are one of the greatest challenges facing our society.”

This is believed to be the first time such an analysis has been used to gauge recent flooding against historic norms in the UK, and the same technique could be used elsewhere to form a wider picture of flooding in Britain in recent years.

Research paper abstract:

Using lake sediment archives to improve understanding of flood magnitude and frequency: recent extreme flooding in northwest UK

We present the first quantitative reconstruction of palaeofloods using lake sediments for the UK and show that for a large catchment in NW England the cluster of devastating floods from 1990 to present is without precedent in this 558‐year palaeo‐record. Our approach augments conventional flood magnitude and frequency (FMF) analyses with continuous lake sedimentary data to provide a longer‐term perspective on flood magnitude recurrence probabilities. The 2009 flood, the largest in >558 years, had a recurrence interval larger (1:2,200 year) than revealed by conventional flood estimation using shorter duration gauged single station records (1:1,700 year). Flood‐rich periods are non‐stationary in their correlation with climate indices, but the 1990‐2018 cluster is associated with warmer Northern Hemisphere Temperatures and positive Atlantic Multidecadal Oscillation. Monitored records rarely capture the largest floods and our palaeoflood series shows, for this catchment, such omissions undermine evaluations of future risk. Our approach provides an exemplar of how to derive centennial palaeoflood reconstructions from lakes coupled well with their catchments around the world.