Sponge cities: a possible answer to the floods (and droughts) of the future
We explore this concept that is gaining momentum to adapt urban planning to the needs of the 21st century.
In this house we have been talking for years about bioclimatism and the need to adapt faster than we are doing to the climate crisis. And a few months ago, our colleague Pedro Guerrero participated in the congress of Public Parks and Gardens (PARJAP). He focused his intervention on the defense of a concept that has become sadly relevant in Spain since the overflowing of the Júcar River devastated Valencia last October. We are talking about sponge cities.
Sponge cities are an urban planning model that takes into account both the climatic conditions and the possibilities offered by nature in order to create solutions based on it.
Overcoming an outdated urban planning model
As Pedro explains, we have totally impermeable cities. Our water management consists of trying to contain water in our piping and sewage system. And to control the watercourses, we need to keep it below the surface. The problem is that when there are episodes of torrential rains or overflowing rivers, the water that can no longer be absorbed by the canalization system has nowhere to go, because the soil cannot absorb it, causing floods that can be as devastating as the one experienced in the Spanish East during the October floodings.
Likewise, the planning of cities follows the requirements of the 19th and 20th centuries: to house as many people as possible in the safest conditions for work. Circumstances, however, have changed. The jobs of today are not the jobs of a hundred years ago. Neither is our lifestyle and what we consider to be decent living conditions.
We keep repeating and hearing that we need cities that adapt to the needs of the 21st century, but what does that mean? Among other things, it means anticipating climate disasters and minimizing their disastrous consequences. As architect Kongjian Yu, one of the great advocates and pioneers of this urban planning model, puts it, you cannot fight against water: you have to adapt to it.
Sponge cities: vegetation + distribution + materials
In these designs, a myriad of concepts related to bioclimate are incorporated, ranging from the distribution of the spaces themselves, incorporating macro and microstructures that allow the soil to absorb water instead of channeling it, to the materials with which these spaces are made.
Many of the materials we use massively in construction and urban planning projects make sense for the function they serve. They are cheap, easy to produce, allow us to build on a large scale and are structurally safe. This is the case of concrete, cement or steel. However, sponge cities involve, among other things, replacing these types of materials with others that favor the prosperity of natural elements and allow the absorption or permeability of water. Also, favor the ideal conditions of thermal comfort to face the extreme events of the climate crisis.
This is indeed the case of clay and terracotta. In our blog we have spoken at length about its hydrothermal and bioclimatic properties, but the summary is that it is a material that meets all the ideal conditions for this urban planning model. That is why it also lends itself as a scientific research material for ecological restoration, for experimentation with models of sustainable architecture, and for large-scale bioclimatic projects.
Retain water when there is a shortage, absorb it when there is a surplus
The sponge city model addresses the two major water issues: droughts and floods. Natural spaces have an incredible capacity to regulate large flows of water, and these cities rely on these same mechanisms of absorption (which is another word for storage) of water in the ground.
In very large cities, large green spaces can be incorporated with provision for both floods and droughts. If it rains torrentially, the soil absorbs water much faster. In case of droughts, the choice of native species and the soil’s ability to store water means that plants survive much longer and with much less water (we have empirically proven this on our own land). When dealing with smaller spaces, subway systems can be used, in addition to greenery, to store that water directly through the soil. In both scenarios, it is essential to have construction and paving materials that allow permeability, either through themselves, as in the case of stratified soils with soil and gravel, or through their joints, as in the case of terracotta bricks.
On top of all this, as Pedro reminded us at PARJAP, sponge cities trigger a chain reaction. Cities become friendlier spaces for children, the elderly, and vulnerable groups, not to mention our furry companions. We need to focus on the ground for many reasons, not least to avoid disastrous consequences such as those we have seen this fall. But being able to minimize the devastating effects of future floods is certainly not a minor objective.
