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At the first glance, the numbers in this infographic might seem entirely random and unrelated. What connects mental health with climate change, and what does either of them have to do with water quality?


Quite a lot, actually. They are all affected in one way or another by the green spaces that we have available to us, and their quality. Especially in urban areas, our “Green Infrastructure” plays as much part of our lives as any other kind of infrastructure we use daily. We just might notice it a bit less. Green infrastructure provides habitats for pollinators, spaces to reconnect with nature and ourselves, it soaks up water, provides shade and stores carbon.

Increasingly under pressure from various sides, it can seem like our green spaces are not being valued as much as they should be. At the same time, the climate is changing as well as the landscape, and we are experiencing the effects of this change.

While mitigation of climate change is important, so is adaptation – we need to transform our cities into resilient places that can adapt to the changes that we know are taking place. Well managed, high quality green spaces are crucial to enable this transformation.

But let’s have a look at what we know about the issues first.

A changing climate in the UK

In a country like the UK, rain is – in most parts – just a part of daily life, and a bit of mizzle has never hurt anyone. However, due to climate change, extreme rainfall events are expected to increase, even if this does not necessarily mean river flows or flooding increases with rainfall flooding (have a look here if you want to understand more about why this is the case). There is no fixed definition of what an “extreme rainfall event” is, as the rainfall in the UK is very variable over different regions – but you can understand it as a downpour that is heavier than you would expect to happen in a number of years in your area, for example a rainfall event that would only have a one percent chance of occurring in any given year, or a 1-in-100 type event.

Where does rain go and what happens to it?

The response of an area to extreme rainfall depends on what this area looks like. While river flooding can often require a few days rain to occur, built-up urban areas tend to respond more rapidly to high rainfalls. This is mainly due to their impermeability: roads and buildings cannot soak up water, and there is little greenspace available in urban areas to infiltrate all the water that falls on a city. Traditionally, pipes and gullies are what takes up rainwater in urban areas and transports it away from the surface, in order to minimise the risk for diseases spreading amongst humans.

What we have come to notice, however, is that our drainage systems are often overwhelmed by the increasing amounts of water they have to cope with during single events. This type of flooding, that occurs when local drainage capacity is overwhelmed by the amount of water it has to cope with, is called Surface Water Flooding (look here for a brief explanation of different types of flooding).

On a natural surface, such as meadows or woodlands, rain would be slowed down by plants before infiltrating into the soil (provided this isn’t saturated, in which case rain would run off). It would then slowly make its way to the nearest watercourse or the groundwater body below, resulting in lower peak flows (that is the highest amount of water flowing through a watercourse in a flood) and lower volumes than we expect from surfaces that are sealed off and result in rapid runoff. The graphic on the left shows the differences between runoff from urban and natural surfaces, and the corresponding differences in river flows.

Draining Away

With high intensity rainfall events expected to increase, we can expect surface water flooding to increase in urban areas, and traditional solutions are failing. There are two ways that water is removed from developed areas traditionally: Combined sewer systems and separated sewer systems.

Depending on the age of a development, rain pipes will often lead into what is known as “combined sewer systems”. This means that foul water, that takes waste for example from toilets, and surface water from roofs and roads are taken away by a combined pipe to a sewage treatment plant (see the graphic on the right, produced by Thames21). This has two negative aspects:

  1. Runoff water is mostly clean and requires little treatment, combining it with foul water increases the volume of water that needs to be treated, therefore increasing cost and energy demand.
  2. During high intensity rainfalls, the volume of surface water that enters the combined sewers can exceed the volume that the pipes are designed to carry. This leads to CSOs – Combined Sewer Overflows – into rivers, or even lifting up manhole covers to release the pressure built up through the high volume of water entering – meaning raw sewage is discharged straight into a river or street.

Most newer developments, especially from 1920 onwards, therefore have separated sewer systems, with one system exclusively dealing with runoff that can be discharged into a watercourse with little or no treatment. While this eliminates or reduces the problems named above, it still means that the water reaches the river much faster and potentially with more volume than in a natural system. In turn, this means that peak flows are high and flow of water is generally larger than it would be expected otherwise.

There can still be issues when sewer pipes are connected the wrong way – these are called misconnections – and pipes that should lead to the sewage treatment plants are mistakenly connected to the surface water system.

This can lead to severer pollution in rivers and streams close to you and have detrimental effects on wildlife. If you suspect that your property might be affected by this, you should get in touch with a plumber who can check and correct this.

Water Quality and Habitats

Water pollution can also simply arise from runoff – rainwater moving over the urban surface picks up pollutants like heavy metals from roads, chemicals from car washes, pesticides or fertilizers from gardens.. Many people don’t realise that drains can lead directly into a river. While all these sources are by themselves minimal, combined they contribute to “diffuse pollution” that can have significant impact on the quality of water and habitat, therefore impacting wildlife as well as humans. In 2013, less than a quarter of waterbodies in the UK was deemed able to support viable ecosystems, and many of them were failing due to pollution caused by the urban environment.

With over a tenth of the UK’s area being urban, poor water quality is not the only way wildlife is impacted by urban areas. While some species are very well adapted to the city environment and can make use of modified spaces, fragmentation of habitats or lack of connectivity between existing spots can make it difficult for species moving around to find new sources of food or breeding areas. Loss of high quality green spaces in cities or degradation thereof are the biggest threats to biodiversity in urban areas and can impact the surrounding environment too.

Green spaces for people

Of course, it’s not just wildlife that needs to find a home in urban areas. Over 80% of the UK population live in cities, and that number is expected to increase. That the need for housing is pressing can be to no one’s surprise, and in Taunton alone a 40% increase in housing stock is proposed over the next few years. Development of this kind has in the past often meant a loss of high quality urban environment: in 2001, almost 40% of urban parks were degrading in quality as a result of reduced spending – and the worst declines were reported in areas of social deprivation, indicating that those who could benefit most from imrpoved green spaces and neighbourhoods have the least access to them. In a 2016 Heritage Lottery Fund study, only a quarter of park managers reported their parks to be improving. At the same time, visits to urban parks are increasing, and the benefits people gain from spending time in a greener environment – improved mental health, for example – are significant.


Each year, one in four people experience a mental health problem, and it seems like we are less able to cope with these problems and stresses we are under as more people report self-harming. One factor that can influence our mental well-being is access to and connection with nature, as research from Exeter University shows (see video on the right).

So, coming back to the first infographic we looked at – Green Infrastructure is what connects all these different topics. From the first drop of rain that falls onto a roof to the last child leaving the park at dusk, green spaces support all aspects of our lives and enable us to enjoy them. While SPONGE focuses on delivering solutions to water-related effects of climate change, using nature-based solutions such as Sustainable Drainage Systems to do this allows us to create so much more.

By making sure our cities are green and full of live, we make sure that we can enjoy them – now and in the future.

If you want to be part of it, have a look at how you can get involved or what the things are you can do.