Climate change is set to halve the level of protection the new £56 million flood defences will give to Sheffield in 50 years.
Sheffield Council unveiled plans for a scheme aimed at reducing a ‘catastrophic’ flood risk to 6,000 households and 2,000 businesses and avoid a repeat of the 2007 floods which killed two people.
But the report which sets out the plans - including renewing culverts and boosting defences - says the increased protection will be reduced over time, due to climate change.
Once completed in 2021, the improvements will give the city a one-in-200 years level of protection, meaning the measures will theoretically defend the city against all floods except the kind of freak floods which have a 0.5 per cent chance of happening in any given year.
But, as little as 50 years later, the protection will be reduced to a ‘minimum acceptable standard’ of just one-in-100 years. The freak 2007 floods were classed as a one-in-150 years event.
The council report states: “At full completion in 2021, the programme will aim to provide a higher standard of protection of up to one-in-200 years for 6,000 Sheffield households and 2,000 commercial properties.
“This standard will reduce over the next 50 years due to the effects of climate change, however a minimum acceptable standard of one-in-100 years will be maintained.”
Green Party Sheffield Coun Jillian Creasy said: “It just shows it’s a moving target, that the defences we are doing now are going to be out of date because climate change is accelerating.”
She said there needs to be more focus on managing flood problems ‘upstream’, adding: “The council is doing what it can in Sheffield and that’s great. I wouldn’t fault that.
“But in Sheffield, because of steep valleys, most of the flooding we get is water in rivers filling up too quickly, so work upstream in the Peak District and on flood plains is really important.”
Coun Jack Scott, cabinet member for environment, said: “It’s right to point out these defences will give us almost total protection.
“But it’s also the case that over the longer term, because of our heating planet, we will be more liable to flooding. That makes it all the more important to first build these defences and, secondly, do as much as we can to reduce our carbon.”