flooding

Changing climate demands new approach to flood risk, say MPs

flooding
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A new report by MPs says the government could be doing a lot better at managing flooding, as well as telling people how much risk they are exposed to as the climate changes

November 1, 2016 — The report comes from the Environment, Food and Rural Affairs (Efra) select committee, a cross-party parliamentary group that scrutinises the work of the Department for Environment, Food and Rural Affairs (Defra) and its related organisations.

In January, Efra launched an inquiry into the winter 2015-16 floods in England. At the time, the committee’s chair, Neil Parish MP, said that the flooding seen in 2015-16 was “becoming all-too-frequent an occurrence”:

Questions need to be answered about whether there are adequate measures in place to plan for frequent, extreme flood events.

Over this year, the committee has gathered written and spoken submissions of evidence on four topics: predicting the future, protecting communities and infrastructure, managing water flows, and planning for floods.

With the evidence now in, the new report describes their findings and recommendations. Carbon Brief takes a look at how climate change features.

‘Already having an impact’

The main focus of the recommendations in the report is for a “new governance model” for how the government manages flood risk in England.

This includes the proposal for a new English Rivers and Coastal Authority – along with new Regional Flood and Coastal Boards – to take over from the Environment Agency on delivering national flood risk management plans. This would “enable a close link between national plans and local aims,” the report says, all held to account by a new National Floods Commissioner for England.

Delving a little deeper, the report highlights climate change as a key reason for improving the way flood risk is managed. It says:

“Changing weather patterns are already having an impact [on flooding],” says the report, referencing the heavy rainfall over the 2015-6 winter and the succession of storms – Desmond, Eva and Frank – that caused flooding in northern parts of the UK.

The report notes that the impact of climate change will continue to increase flood risk in the UK:

More people are likely to be at risk in future as climate change affects weather patterns and sea levels. Rainfall is predicted to become more frequent and more intense; peak river flows could be more than twice current levels in some English regions by 2070.

Research into the UK winter floods in 2013-14, for example, has already showed that climate change made the sustained wet and stormy weather 43% more likely.

The report doesn’t discuss how the impacts of climate change should be included in flood risk assessments. It does, however, refer to the extreme rainfall modelling work carried out by the Met Office for the government’s recent National Flood Resilience Review (NFRR).

The NFRR was set up following severe flooding during the wettest December on record in 2015. In September, it published its findings on flood risk over the next decade and how the UK could be better prepared, as the Efra report describes:

The NFRR published in September, after we finished taking evidence, has reduced some uncertainties. It concluded that, based on Met Office modelling, it was plausible that rainfall between 20 and 30% higher than normal could be experienced over the next 10 years.

However, as Carbon Brief identified, the extent to which this modelling work recognises the role of climate change in extreme rainfall has caused quite a lot of confusion. While the expectation for bouts of rainfall 20-30% heavier than today takes into account the contribution from climate change to date, it largely reflects what we can expect to see within the bounds of natural variability – not future climate change.

Communicating flood risk

Another of the report’s recommendations deals with how the level of flood risk is communicated to the public.

Typically, flood risk is described in terms of its “return period”. This is a measure of how often you would expect a flood event of a given size to come around. For example, a “one in 50-year” event can be expected to occur, on average, about once every 50 years. Whereas a one in 100-year event is more extreme and occurs less often – hence the longer return period.

But this can be confusing, the report says:

It is hard to interpret from this information the risk of flooding for any particular home or community at any particular time; individuals may not therefore appreciate that they need to take steps to reduce their own risk.

For example, a “one in 50-year” return period can give the impression that once there has been a flood, there won’t be another one for another 50 years. Whereas, what a 50-year return period actually means is that there is a 1 in 50 (or a 2%) chance that a flood of a given severity would occur in any one year. You could have ‘one in 50-year’ floods in consecutive years and nothing for the next 100 – it’s just that over the long-term it works out at once every 50 years.

Also, perhaps counterintuitively, if the risk of flooding increases, then the return period goes down. So, for example, a one in 50-year flood might become a one in 30-year event because of climate change, signifying that an event of this magnitude is happening more often.

Although it’s not perfect, there isn’t an obvious way around using this approach, says Prof Myles Allen, professor of geosystem science at the University of Oxford, who wasn’t involved in the report. He tells Carbon Brief:

There are all sorts of different ways of communicating risk, but in the end, you’ve got to communicate odds…Perhaps ‘one in a hundred chance of being flooded next year’ is a better way of putting it than a ‘one in a hundred year’ flood – but it’s communicating the same information.

And Allen thinks that the public aren’t as confused by return periods as the Efra report suggests:

Giving public talks, my impression though is that the public understands probability much better than they’re generally given credit for.

However, the Efra report argues that an alternative is needed:

We recommend that the Met office and the Environment Agency set out by the end of 2016 a simpler system for explaining flood risk. The EA should also publish maps which include not only whether a place is at risk of flooding but also the likely depth of flood water and duration.

Real-time

The Efra report also recommends that the Met Office and Environment Agency make greater use of “real-time” data for flood warning systems:

We recommend that the Environment Agency report by July 2017 on how it can work with the Met Office to collect more detailed real-time data on rainfall and river levels.
We further recommend that systems such as those being developed in Somerset to feed real-time data into live flood forecast warnings are deployed across England at the earliest opportunity.

In response to the Efra report, the Met Office says it “welcomes” their recommendations on both real-time data and communication of flood risk:

These are broadly consistent with the relevant outcomes of the National Flood Resilience Review and as such we will continue to work closely with the Environment Agency and relevant other partners to address these.

by Robert McSweeney | Carbon Brief