Aapo Pihkala

Stormwater management is easily treated as a technical detail, even though it is also a very tangible form of economic risk management. When the capacity of a system is exceeded, water will find a route. The question is whether a safe place has been designed for it, or whether it ends up in basements, streets and buildings.

This is why water needs to be considered beyond the boundaries of an individual site. What matters is understanding the catchment as a whole: where the water comes from, where it flows, where it can be retained and what lies downstream. Stormwater management is also about both quantity and quality. The presence of a sensitive water body nearby can change the nature of the design problem considerably.

One advantage of nature-based solutions is that water can become a visible part of the landscape. It can be retained in depressions and wetlands, made available to vegetation, and returned to the soil and the cycle of evapotranspiration. The performance of the system can also be observed. Problems in buried infrastructure may only become apparent once water starts causing symptoms somewhere else.

Pipes are part of the solution, but a city cannot build its flood resilience around pipes alone. During an extreme rainfall event, the water has to go somewhere. Good planning decides where that place will be before the rain arrives.

To me, nature-wise design does not mean giving up the design of a yard or its landscape architectural form. At its best, several objectives are achieved at the same time: the yard provides habitats for different species, gives space to natural processes, and remains functional, pleasant and beautiful for people.

Even a small yard matters. A large share of land in Espoo is privately owned, which means that private yards and housing-company yards are also part of the city's ecological networks. A courtyard in an apartment building can provide everyday contact with nature for many people while also contributing to the surrounding green structure.

Nature-wise design does not usually require major investments. Often it is also about what is left undone: not everything needs to be cut, cleared or built into a finished state. When more space is given to natural processes, the need for maintenance can also decrease.

Even a small yard is part of urban nature.

I think good planning starts by identifying existing trees before the locations of buildings are fixed. If a site already has a healthy mature tree, one of the first questions should be whether it can be retained and what that means for the placement of new development.

It takes seconds to draw a new tree symbol on a plan. Growing a large tree takes decades. Only a substantial canopy provides significant shade, evapotranspiration and an effect on the local microclimate. A tree also needs real space both above and below ground. In a dense city, that space does not magically appear later.

The benefits of trees are also local. Finland has plenty of forest, but trees elsewhere do not shade a hot street or courtyard in another neighbourhood. The value of urban trees depends precisely on where they grow.

Landscape conditions should therefore be considered while there are still genuine choices to be made. Not after the buildings and streets have already been decided, with the trees left to fit into whatever space remains.