Blue-green infrastructure (BGI) creates environments that are more resilient to the effects of climate change. They reduce flood risk by creating green spaces that absorb more water, alleviating pressure on pipes and sewage systems.

You can read our introductory interview with Emily O’Donnell, Assistant Professor in Climate Change at the University of Nottingham, here. In this section, the interview covers ways in which you can implement BGI at home, and the research that is being carried out right on your doorstep.

What are the things I could do in my garden or yard to help?

Gravel is always better than concrete for paths and driveways, as it allows some of the rain to move into the soil. However, the easiest thing to do is to install a water butt onto any pipes that are draining rainwater from roofs, preventing water from going into the sewers. For instance, it can be helpful if you disconnect a pipe that may be connected to the roof of a garage or conservatory, so the water doesn’t go into the system.

And of course, if you collect the water, you can use it to water your garden and maybe save a little bit of money there. If you can prove to Severn Trent that no water landing on your property is going into the external drains, you can get a small discount on your water bill. But you’ve got to make sure that any pipes you want to disconnect are not used to take away both rainfall and sewage. In new houses there tends to be two separate systems, but we have a lot of older houses where some pipes do both jobs.

The Severn Trent website has the following information under the question ‘What is surface water drainage?’: ‘The rain that falls on your roofs, yards and other parts of your property drains away to the public sewers. This is called surface water. We include the cost of removing this surface water in the sewerage charges on your bill. For some customers, surface water or groundwater may not drain into the public sewer. If you are in this category, you may be able to claim for a reduction in your sewerage charges.’

Can you tell me about green roofs? I presume that if I was to construct one of these, I’d need a flat roof?

Yes, or slightly sloping.

You can find information on how to build them online, (such as BBC - Build a Green Roof).

You need a layer of soil and some vegetation which will absorb the rainwater and remove it via evapotranspiration. Of course, the building has to be strong enough to hold the weight of the soil, the plants and the water, and I know people who have green roofs and have done it themselves. There should also be some kind of overflow, so that if there is a massive rainstorm, and the soil can’t take it all, the water has somewhere to go.

The thing about green roofs is that they’re really good for pollinators, and if you get lots of green roots dotted around it creates pollinator pathways. You see a lot more green roofs on bus stops now, and they’re mainly for pollinators rather than water, although they will stop a certain amount of water going into the sewers.

You can read about the greening of Sheffield’s bus shelters, carried out by Groundwork here.

Shed with a green roof

Tell me more about the other aspects of this technology, beyond the question of water drainage.

The most important aspect of designing Blue-Green infrastructure is its potential for multiple impacts. Can it be a site for pollinators? Can it help reduce urban heat?

Green roofs, for instance, are effective at trapping heat in the winter and preventing heat from entering buildings in the summer, which is why many buildings incorporate them. The focus tends to be on energy efficiency, rather than water management. But, this issue of extreme heat is really important.

Recently, we did a project mapping the heat hotspots in the Nottingham during the 2021 heatwave, using satellite temperature data. The data reveals that areas with concentrations of housing and little green space experience significant heat hotspots. Larger areas of green space, such as parks and reservoirs, have a cooling effect that can extend up to three hundred meters.

Areas where you've got water or trees have the biggest effect in stopping heat getting to the ground.

I'm looking at whether we could reduce these temperature risks by putting more green space into Nottingham.

The Blue-Green infrastructure that would be best for managing heat would be trees because they provide shading. The problem is, to get the most shading from trees, you need mature trees— and that takes time.

Nottingham is keen to know if their trees have an impact on heat; they did a big survey of all the trees in Nottingham, all their sizes and shapes, to see if the areas where they've got lots of street trees has an impact. It’s not just about shading, and stopping the sun bouncing off of the tarmac, but the act of evaporation is also a cooling process. As the water in the leaves evaporates in the heat the process of turning that water into gas requires energy, which the trees are taking.

Some people complain about trees blocking out the sun in their gardens. They’d rather have them chopped down, so they can sit in the sun on the days when its shining.

Yes, it’s a challenge.

Most people don't really think about heatwaves. A colleague in the Psychology Department interviewed people after the recent heatwave, and was told of impacts that you don't really think of. Lorry drivers who couldn't go to work because they don't have air conditioning; people on zero hours contracts who had to miss a day of work because it was too hot; schools closing; people not being able to leave their windows open at night because of risk of burglary. There are so many problems with heat and the U.K. is not ready for heatwaves.

Nottingham, like any city, is a heat island. Heat concentrates, and as you get further out of the city, it cools down a bit because you've got more green space and less activity, such as car exhaust fumes, which all add to the heat.

I don’t think everyone understands how to deal with heat; remembering to do simple things like closing the curtains to stop the sun shining in. We don’t have shutters on our windows, maybe one day we will. People leave windows open to get the breeze, but if the air outside is hotter than inside, you're bringing hot air into the house.

During the heatwave, I could see many houses with their windows open. You should close your curtains and close your windows during hot sunny days, and open your windows during the night or the early morning when the temperature is cooler outside. People don't think about it because we don't have heatwaves very often. And we can't move towards everyone having air conditioning because that uses up so much energy and is an additional financial cost. Even if it was solar powered the excess heat goes out into the environment. It seems like our infrastructure can’t deal with any kind of weather that strays outside of a reasonably narrow range of possibilities.

Something that I don't have the answer to, and which is driving my future research, is if you have lots of smaller Blue-Green interventions like bioswales, does that add together to create some kind of temperature effect?

Something else we've been talking to the council about is, where are the cool spots in Nottingham and can people get there easily? Maybe when we do have heatwaves, people need to get out of their houses and go somewhere else; and there needs to be designated cool spots in the city where people can go that doesn't cost them anything. We looked at which types of people are more vulnerable to heat; and its older people, children under four, people with existing health conditions; with heart conditions or respiratory problems that get worse during heat. There are a lot of risks to certain types of people. When the temperature in your house is warmer than it is outside, you need to leave your house.

Click here to keep reading about developments in Blue-Green Infrastructure in Nottingham.