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03 February 2014
High water mark

High water mark

It is likely that floods would have dominated the winter headlines even without Ukip councillor David Silvester’s home-grown version of climate science.

In December, Scotland experienced 522mm of rainfall, around 240 per cent of the monthly average.

Within the space of a month SEPA was forced to issue 360 Flood Alerts and Flood Warning messages – equivalent to 95,785 SMS or telephone calls – to those registered through its Floodline warning system.

It is estimated that one in 22 residential properties in Scotland is at risk of flooding, with the annual damage estimated at costing between £720-£850m.

And with media images of families fishing belongings from flooded homes and people using boats rather than cars, bikes or on foot, the issue is still pressing and worrying for those at risk.

Nigel Don, MSP for Angus North and Mearns, has seen the effect of flooding in his constituency first hand, particularly in Stonehaven and Brechin.

“Last Sunday evening I walked down River Street in Brechin and I saw people piling their possessions up on tables in the ground floors, knowing that their back gardens were already under water. We were in that position last winter and now it is happening again.

“Stonehaven too has rivers with a high risk of flooding; it has been underwater twice in the last couple of years. My office has been flooded in the past. It feels like it is happening a bit more often than it was and certainly far more often than you would like.”

The feeling that flooding is becoming more common is widespread, and it is easy to reach out to climate change as an explanation.

In theory, warmer temperatures allow more water to build up in the atmosphere – increasing the probability that when it rains, it will pour.

But the science is not as simple as that.

Alex Hill, the Met Office’s Chief Adviser to the Scottish Government, is wary of drawing a direct line between climate change and increased flooding.

“Yes, if you put more water into the atmosphere it has to come out somewhere, and if you are underneath it you will get wetter. So what we are looking at is a change. Although the average amount of rain at certain times of the year has gone up an unnoticeable amount, the change is in the extreme ends – they become more frequent and we can suggest that is what has happened.

“Attempts to link specific weather events to climate change – attribution science – is almost impossible in Scotland because it such a tiny place. Bigger events we have seen over the last couple years – the big heat wave we saw in the US in 2013 – is more likely to have been linked to climate change. The probability of that heat wave is four times more likely because of climate change.

“In 2011 the flooding in Pakistan was attributed. But these are very big events, in places larger than Scotland.”

But even if the line between floods in Scotland and global climate change is blurred – it is enough to know flooding is indicative of a pattern associated with climate change. In other words – it makes sense to prepare for more water arriving.

The most obvious way to defend against flooding is through barriers and physical defences.

Perth has a long history of severe flooding incidents, including in 1993 when significant damage was caused to communities beside the river and large numbers of people were evacuated from their homes due to the very high water levels.

The city completed its flood defence scheme in 2001, at a cost of £26m, to cope with the future risk of flooding around the River Tay.

The scheme, at the time the largest in Scotland, comprises major flood defences – including flood walls and embankments, flood gates, flood storage ponds, culvert improvements, pumping stations and drainage measures – extending along the River Tay, River Almond and Craigie Burn.

It was designed to protect Perth against the highest flood on record, which occurred in 1814 coinciding with the 1 in 100 year high tide. 

While providing a case study in the array of defences available, the Perth system also provides an example of how flood management worked prior to the Flood Risk Management (Scotland) Act of 2009.

It was massive flooding across Europe in 2002 and 2004 – in which thousands were displaced and dozens killed – which gave the impetus to create a new framework for tackling the danger of flooding.

2002 also saw the East End of Glasgow hit by flash floods, exposing the shortcomings in the city’s antiquated storm drains and leading to the evacuation of around 200 people.

The EC Floods Directive followed in 2007, giving the Scottish Government the opportunity to build new legislation – the forementioned 2009 Act  – that drew together disparate pieces of Scottish flooding law.

While also matching EC rules, the Act ensures that different organisations responsible for different bits of flood risk management must pull together.

SEPA is one of the bodies responsible for mitigation, and to David Faichney of the agency’s flooding unit, the new legislation is a big improvement.

“In planning how to deal with the risk, we have to deal in river catchments or coastal areas, because these are the units we can manage flood planning. There’s no point thinking about flood risk in Perth without thinking of the whole River Tay, for example – you have to think of what you can do in the whole River Tay catchment.

“This means that local authorities have to deal with the risk across boundaries, in what are called Local Plan Districts – catchments that have been pulled together, because local authority boundaries don’t always follow rivers. Sometimes we have seven different local authorities working together.

“In terms of hierarchy, first, you want to avoid flooding, but if you can’t avoid it, then you want to protect people, and if you can’t protect them then you can at least warn them that a flood is coming. So first, don’t build on flood plains, then if you can’t prevent the flood then you can use the warning system to help them know when to take action.”

The warning system has made leaps forward in recent years.

The Scottish Flood Forecasting Service, run in cooperation with the Met Office, has improved flood warning lead times. This brought the ability to provide warnings for rivers – such as the River Carron at Stonehaven and the Ruchill Water at Comrie – where it was previously impossible.

SEPA also works with the Met Office through the Scottish Flooding Forecasting Service to send out the daily Flood Guidance statement to around 500 recipients across responder organisations, to help them plan for flood risk over the next five days.

This was of huge benefit in the run-up to the floods that occurred this year around Christmas time.

To Faichney, warning is a key tool in mitigating the worst effects of flooding.

“The big storm surge down the east coast in 1953 killed over 300 people in Britain. There was a similar size surge in December and only around 12 died – partly because of better communications, better flood defences, better preparation and better flood warning.”

Flood warnings are essential, but the long-term aim must be to prevent water building around houses and businesses in the first place, by taking flooding into account in town planning, as well as changing the way we manage wild spaces.

“We have to look at what we can put in place in different catchments to reduce risk as much as possible,” says Faichney, “how we manage land, how water runs off of it, where you can capture water, where you can safely flood areas upstream to protect things downstream.

“Anything that slows the passage of water down through our catchments has the potential to contribute to mitigate flooding.” 

Tree roots absorb and disperse water, it takes longer for a raindrop to make its way down a tree into the ground and they can also act as a barrier if they are on flood plains.

Research carried out by the Flood Risk Management Consortium indicates that water can be absorbed 67 times faster by trees than normal grassland. In a case study, based in Wales, it was estimated that an optimally placed belt of trees could reduce peak flow by 29 per cent.

Farmland, by contrast, is much harder for water to permeate than trees or scrubland, allowing it to run across the surface and arrive downhill much more quickly.

The problem is exacerbated by the effects of climate change, which has extended the growing season. Although, with more land available, this is clearly good news for farmers, it has also increased the risk of floods.

Changing the way land is used will require the cooperation of multiple agencies, businesses and private individuals across Scotland – with the Forestry Commission recently having been made a responsible authority, forcing it to take flood considerations into its decision-making.

But until measures to adapt are put in place and while water keeps falling, flooding will re-occur.

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