3-30-300: This is how you can find out how much nature there is in your city

How do you feel when you look out a window and see the treetops swaying in the wind? Or when you walk through a city where there are more trees than cars? Perhaps on a summer afternoon, in the shade of a park, with friends.

You probably feel good. That view isn't just an aesthetic whim: it's what our bodies crave. And today we know how to satisfy that craving better than ever. Here's the 3-30-300 standard: cutting-edge green! The most innovative cities are adopting this new urban planning standard to design spaces that serve the well-being of their citizens.

To understand it, we spoke with Sandra Calduch-Fernández , a research support technician currently pursuing her doctorate at CREAF . Since 2021, she has been working on the analysis of green infrastructure and, specifically, on how to apply this rule to the territory. She explains that " the rule was promoted by researcher Cecil Konijnendijk in 2021," and that " it serves as a guide for integrating nature into cities equitably , so that it offers maximum benefits to a citizenry that is often far removed from natural spaces."

It is based on three elements, the three types of contact with nature that we can experience:

• 3 - The visibility of greenery . See at least three trees from your window .
• 30 - Exposure to greenery . A neighborhood with at least 30% tree cover .
• 300 - Access to green spaces . Having the nearest green space within 300 meters .

The 30% is measured at the neighborhood level , not the city level, to ensure fairness. “A peri-urban forest like Collserola in Barcelona could distort the data,” explains Sandra Calduch-Fernández. “At first glance, it might seem that there is tree cover, but then, depending on the neighborhood, there isn’t enough.”

And the 300 won't settle for just any space : it has to be public and of high quality . "By quality, we mean that they have to be spaces of sufficient size , with a diversity of species, with trees that provide shade , and that also have services for the public , whether they are play areas or leisure spaces," he explains.

Knowing the benefits of urban green spaces is one thing; putting them into practice is quite another. How do you plan a city so that these green spaces reach everyone equitably? Calduch-Fernández emphasizes a key point: the 3-30-300 guideline is a guide and doesn't mandate anything . "It can help city councils get their bearings: what is the current state of their green spaces, how much there is, and how it's organized," she explains.

Each municipality decides how to implement it based on its available resources. And that's where the first difficulty arises. Calduch-Fernández points out: "the availability of data that administrations can use to make these calculations , because not all municipalities have the necessary information—such as up-to-date tree inventories or records of public spaces ."

There is also a fundamental obstacle: the standard originated in Northern Europe , and this creates difficulties, especially regarding elements 3 and 30. It's not just a question of space for planting in compact cities . Climate also plays a role: in semi-arid or Mediterranean areas, tree growth is limited by water availability.

Lack of space for planting is not a death sentence. Sometimes a limitation creates new possibilities . As Sandra Calduch-Fernández reminds us, “any green space, however small, can count: the interior courtyard of a community, the rooftop of a building, a facade.”

In fact, new buildings are already required to incorporate trees or green spaces. And where a tree isn't feasible , other solutions are available: green roofs, vertical gardens, community gardens, vegetated tree pits, and rain gardens (revegetated porous pavements that absorb stormwater and reduce flooding).

Many of these solutions involve the residents of the neighborhood . In tree pits, for example, "some city councils are responsible for distributing the tree species, and then it's the residents who take care of maintaining, watering, and caring for them," explains Calduch-Fernández. Citizen participation can also be factored into the very design of the regulations . As Calduch-Fernández points out, this can be done through surveys about which trees are visible from homes or the quality of nearby parks. And it can influence the decision about what to create in each location ; a community garden here, a park there.

The underlying challenge is one of livability. It is estimated that by 2050, 70% of the world's population will live in cities , and heat waves and droughts will become longer and more intense. If more green space is not incorporated into cities, living in them will become unsustainable. We are talking about a right: fair and equitable access to green spaces is already included among the Sustainable Development Goals. The question this raises is, in reality, a call to action: can we truly afford to continue planning our cities without first considering the green spaces that will make them livable?

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