Prepare for more floods - in ways we are not used to - that's the message from experts at Durham University who have studied rainfall and river flow patterns over 250 years.
Last summer was the second wettest on record and experts say we must prepare for worse to come.
Professor Stuart Lane, from Durham University's new Institute of Hazard and Risk, says that after about 30 to 40 less eventful years, we seem to be entering a 'flood-rich' period. More flooding is likely over a number of decades.
Prof. Lane, who publishes his research in the current edition of the academic journal Geography, set out to examine the wet summer of 2007 in the light of climate change. His work shows that some of the links made between the summer 2007 floods and climate change were wrong. Our current predictions of climate change for summer should result in weather patterns that were the exact opposite of what actually happened in 2007.
The British summer is a product of the UK's weather conveyor belt and the progress of the Circumpolar Vortex or 'jet stream'. This determines whether we have high or low pressure systems over the UK. Usually the jet stream weakens and moves northwards during spring and into summer. This move signals the change from our winter-spring cyclonic weather to more stable weather during the summer. High pressure systems extend from the south allowing warm air to give us our British summer.
In 2007, the jet stream stayed well south of its normal position for June and July, causing low pressure systems to track over the UK, becoming slow moving as they did so. This has happened in summer before, but not to the same degree. Prof. Lane shows that the British summer can often be very wet - about ten per cent of summers are wetter than a normal winter. What we don't know is whether climate change will make this happen more in the future.
However, in looking at longer rainfall and river flow records, Prof. Lane shows that we have forgotten just how normal flooding in the UK is. He looked at seasonal rainfall and river flow patterns dating back to 1753 which suggest fluctuations between very wet and very dry periods, each lasting for a few years at a time, but also very long periods of a few decades that can be particularly wet or particularly dry.
In terms of river flooding, the period since the early 1960s and until the late 1990s appears to be relatively flood free, especially when compared with some periods in the late 19th century and early 20th Century. As a result of analysing rainfall and river flow patterns, Prof. Lane believes that the UK is entering a flood rich period that we haven't seen for a number of decades.
He said: "We entered a generally flood-poor period in the 1960s, earlier in some parts of the country, later in others. This does not mean there was no flooding, just that there was much less than before the 1960s and what we are seeing now. This has lowered our own awareness of flood risk in the UK. This has made it easier to go on building on floodplains. It has also helped us to believe that we can manage flooding without too much cost, simply because there was not that much flooding to manage."
He added: "We have also not been good at recognising just how flood-prone we can be. More than three-quarters of our flood records start in the flood-poor period that begins in the 1960s. This matters because we set our flood protection in terms of return periods - the average number of years between floods of a given size. We have probably under-estimated the frequency of flooding, which is now happening, as it did before the 1960s, much more often that we are used to.
"The problem is that many of our decisions over what development to allow and what defences to build rely upon a good estimate of these return periods. The government estimates that 2.1 million properties and 5 million people are at risk of flooding. In his review of the summer floods Sir Michael Pitt was wise to say that flooding should be given the same priority as terrorism."
Professor Lane concluded: "We are now having to learn to live with levels of flooding that are beyond most people's living memory, something that most of us have forgotten how to do."
Flooding is one of the issues covered by the Institute of Hazard and Risk Research at Durham University where Prof. Lane is a resident expert. The IHRR, which launches this week, is a new and unique interdisciplinary research institute committed to delivering fundamental research on hazards and risks and to harness this knowledge to inform global policy. It aims to improve human responses to both age-old hazards such as volcanoes, earthquakes, landslides and floods as well as the new and uncertain risks of climate change, surveillance, terror and emerging technologies.
Prof. Lane's research is funded by the Willis Research Network, an innovative collaboration between universities worldwide and the insurance industry, and the The UK Research Councils' Rural Economy and Land Use Programme.