How Sheffield's green schemes are leading the world in addressing climate change - 'We're getting a name for something very different'

"The number of towns and cities that have been to see us has been phenomenal, frankly," he says. "It's getting to the point where I'm almost becoming a tour guide rather than somebody designing spaces in the city centre."

Delegates from Malmö in Sweden – often lauded as the world's most sustainable nation – spent four days in Sheffield to glean tips, a group from South Korea has flown over, and representatives from Japan and the Netherlands have visited to see how measures to combat global heating can be built into everyday settings.

"We're a getting a name for something which is very different," says Zac.

The main attraction is Grey to Green, the project to transform nearly a mile of semi-redundant roads into a network of sustainable drainage and rain gardens - little islands bursting with colourful flowers and lush greenery.

But Zac's department is responsible for much more, from the radically overhauled railway station forecourt to Sheffield's riverside 'pocket parks' and the attractive public spaces in the Heart of the City II redevelopment scheme.

Climate change, he says, has been at the forefront of council officers' minds 'for a long time', but the devastating floods of 2007 marked a shift in attitudes.

"It was definitely a wake-up call. In the city, people started thinking ‘Is there a new way of doing things?’ In 2008 the big opportunity came where we pushed the ring road further out."

Moving the inner ring road cut the volume of traffic on streets like West Bar, Snig Hill, Castlegate and Exchange Street, meaning fresh ideas were possible.

"We could just do nice granite paving with lollipop trees every 10 metres and it would have looked lovely, but we thought we could do more to start thinking about a new vision for what a street can be in a city for the future," says Zac.

Work on the first phase of Grey to Green began in 2016, and the focus has now shifted to the next stage on Castlegate. Nearly £10 million is being spent on the two sections.

Specimens such as birch trees and purple loosestrife – which grows in wet environments but can cope with long dry spells – were picked to be planted in partnership with Prof Nigel Dunnett of Sheffield University, an expert in eco-friendly horticulture.

"Last year we didn't water at all, but it was our dryest and hottest summer on record. These systems have to sustain themselves. This year they've almost responded even better," says Zac.

"We're looking at species that are flowering much sooner, and later, so you increase that diversity of pollen and nectar for invertebrates. When you look at Government statistics for wildlife it's pretty damning really, we've got a massive decline in everything. If you don't start with the invertebrates then the birdlife and everything else doesn't follow on."

Drainage capabilities - intended to fend off flooding - are at the core of Grey to Green. Any water that isn't filtered by the scheme is discharged directly into the River Don.

"We're not having to push relatively clean run-off road or footpath water down into gulley drains to flash it away to be treated quite expensively," says Zac. "We're treating it on-site."

There have been other benefits too, such as better air quality, 'city cooling' – literally bringing down temperatures with vegetation - and tackling the scourge of microplastics.

"There's a lot of German and Danish studies saying the biggest source of microplastics isn't bottles or anything else, it's car rubber tyre," Zac says. "We're trying to capture those, locking them up in our planting systems. Even if we can't treat them, we know where they are and they're not going anywhere, effectively."

Sheffield's pocket parks, meanwhile, combat flooding on a bigger scale - tiered seating doubles up as a zone for excess water to pool. The first was created on Nursery Street, where the Don burst its banks in 2007, causing the Wicker to be submerged.

"We could have just built a big flood wall against the riverside, but actually we owned that land," says Zac.

The Porter Brook was then uncovered for a further park at the junction of Matilda Street and Sidney Street.

"We've got brown trout back in the river there, there's loads of wildlife in that relatively small section of the waterway," Zac says.

"There are lots of students living around there who don't really have direct contact with anything wild, if you like."

Designs are in the pipeline for another pocket park that would involve opening up a 100-metre section of the River Sheaf where Sheffield Castle used to stand.

As well as being ecologically sound, such projects ensure the city looks appealing to potential investors, Zac says, a strategy his team has adopted for years.

"Initially it was about trying to create a new identity for the city almost, going back to 2000. The city centre was on its last legs from the collapse in the 80s with unemployment, the steel industry going down and Meadowhall sucking a lot of the life out of the city centre. We've then evolved. It's not just about inward investment any longer, it's about climate resilience and all the other things we can bring in."

The 'next big leap', as Zac puts it, is the route across Sheffield station to Park Hill and beyond. A new bridge, and an extension of Grey to Green, have been mooted.

"As a cycle route, from the station to Kelham Island and out into Hillsborough, it's really exciting," he says.

And there is the pressing need to reinvent Sheffield's shopping streets as retailers wobble.

"If it's not about retail, why do you want to visit? Can the city centre become a garden and park space? It's more about enjoyment, climate change resilience and healthy living," says Zac. "It's hopefully going to set us apart from other cities and be identifiably Sheffield."

Ultimately, Zac says, no-one really knows the definitive answers that would absolve all worries about climate change.

But he warns: "You can't just sit there and think everything's going to be OK."