A new study assessing flood risk damage across the UK has just been published. It came out at the same time as the Intergovernmental Panel on Climate Change (IPCC) synthesis report issued its “timebomb” warning and called for “deep and urgent cuts” to greenhouse gas emissions across all sectors.
Increases in flood risk damage look likely
The IPCC report finds “there is a more than 50% chance that global temperature rise will reach or surpass 1.5 degrees C (2.7 degrees F) between 2021 and 2040 across studied scenarios, and under a high-emissions pathway, specifically, the world may hit this threshold even sooner.” It will be used to guide the COP-28 talks in the United Arab Emirates at the end of the year.
Meanwhile, the UK-focussed A climate catastrophe risk model for UK flooding provides the most detailed analysis yet of potential flooding hazards across the country if things do not change for the better. The study, led by the University of Bristol and global water risk modelling leader Fathom, reveals the first-ever dataset to assess flood hazard using the most recent Met Office climate projections which factor in the likely impact of climate change.
Its findings show the forecasted annual increase in physical damage to property and businesses that can be attributed to climate change-driven floods in the UK can be kept below five percent above recent historical levels. But this is only on the proviso that all countries in the world fulfil the ambitious pledges they signed up to at COP26 in Glasgow in 2021 and also that countries, including the UK, which made further Net Zero commitments, actually achieve these on time and in full.
If the COP26 and Net Zero promises are not collectively met, the study shows the annual cost of flooding in the UK could grow by between 13 and 23 percent, depending on the levels of extreme climate projections factored in.
Climate change impact
Lead author professor Paul Bates, Fathom Chairman and professor of hydrology at the University of Bristol, said: “This flood model gives us for the first time a more accurate and detailed picture of the impact of climate change on the risk of flooding across the UK. The results are a timely warning to the country’s political leaders and business sector that global commitments to significantly reduce carbon emissions must be taken very seriously, and ultimately take effect, in order to mitigate increased losses due to flooding.”The sophisticated data has also highlighted the places in the UK where risks will increase most rapidly, even under the best-case scenario where global warming is limited to around 1.8 degrees C. These include South-East England, South Wales, North West England and Central Scotland, especially densely populated cities such as London, Cardiff, Manchester, Glasgow, and Edinburgh, where damage increases of more than 25% are possible.
Conversely, the new model indicated flood hazards in North-East and Central England as well as Eastern and Northern Scotland change very little from the present day.
Flood management policies
The model’s estimates of historical flood risk, which are based on actual river flow, rainfall and tide-surge observations as well as climate model projections, match well with data on flood losses from the Association of British Insurers and shed new light on the financial toll of flooding.
Previous studies by other research groups have already revealed that historical UK economic losses due to flooding have been three times less than government estimates, but this is the first time the observed losses have been replicated and corroborated by a computer model.
“Although the most optimistic climate scenarios see only modest increases in flood losses at a national level, these new data demonstrate how this conceals dramatic variations across the country, with some places seeing large changes and others very little,” explained professor Bates. “This is a result of changing patterns of future rainfall, river flow and sea level rises, which all contribute to the regional differences we predict. We found that flooding increases most in places where risk is already high. It means the best thing we can do to prepare for the impact of climate change is to strengthen flood management in currently at-risk areas, which will bring immediate economic and social benefits as well.”
The team of researchers plan to produce analysis for other countries across the world, furthering international understanding of how climate change is affecting flood risk globally.
Prioritising flood risk
Co-author Dr Ollie Wing, Fathom’s chief research officer and Honorary Research Fellow at the University of Bristol, says the study confirms Fathom’s UK Flood Map and contains a greater level of detail and nuance than any previous comparable work. It represents what is currently a best understanding of the UK’s evolving flood risk landscape, setting out a framework for building complex and robust present day and future flood models, providing new insight into the impact of climate change on future flooding.
“The modelling provides clear evidence that flood risk needs to be a bigger international priority and that current policy doesn’t go far enough,” she stated. “While the majority of the nation’s future flood risk is an extension of what exists today, it is strongly in the UK’s interest to exercise leadership in global carbon emission reduction efforts, both by example and as part of global diplomatic initiatives.”
It is also the same methodology used for Fathom’s UK catastrophe model, known as Fathom-UK CAT, and represents a first for accurately quantifying present and future flood losses. The report concludes that the UK is not well adapted to its existing flood risks, let alone any further increases that climate change will bring. It says that because most locations at peril of future flooding are already at risk now, it follows that strengthening flood management in already at-risk areas is the best option to prepare for climate change driven flooding events.
Bill McGuire, professor of geophysical and climate hazards and author of Hothouse Earth — An Inhabitant’s Guide says a hotter world is a wetter world. “For every degree Celsius temperature rise, global mean precipitation goes up by between one and three percent and if this additional rainfall were spread out evenly across the world and over time it would be less of a problem,” he writes. “The reality is, however, that rain is now falling in shorter, more intense bursts, which provide the ideal conditions for flood development. In particular, torrential downpours are conducive to flash flooding, whereby water overwhelms natural and artificial drainage systems and flows across the surface with little penetration.
“Extreme rainfall events that happened once every decade now occur every 7.5 years, and this frequency will reduce further if the world continues to follow a business-as-usual pattern,” he warned.
