From necessity to project: the design of public space for water control and climate change mitigation

Abstract

Substituting natural areas for paved surfaces typical result of urbanization, not only increases the existing environmental problems in our cities. The severity of flooding, lack of groundwater recharging, erosion of natural water channels, increased temperatures and heat islands, the fragmentation of natural habitats, urban segregation, light pollution and increase of car use with the consequence of air pollution are merely some of the consequences to which this contributes.

Designing correctly the urban public spaces, their materials, permeability and different levels of vegetation, and following some good practice guidelines, would help to mitigate all these negative effects. A good example in this field, are the "water squares" developed in northern Europe, mainly in Rotterdam, a city that is strongly affected by its complex relationship with water. These squares, designed as multifunctional public spaces, have the task of capturing rainwater and becoming, in the case of heavy rains or floods, like detention basins that progressively filter the water to the subsoil, alleviating the problem of overflowing the sewer system. When there is no water, they remain empty and function as relational areas or playgrounds, highlighting the benefits of a dynamic design of the space that is not only projected for a single function, but is capable of transforming according to necessity. In another order of importance, maybe secondary in terms of quality as a public space but vital in terms of the amount of surface they occupy in our cities, parking lots can have a main role as well, as different projects and studies in the last decades have pointed out, to contribute to reverse the consequences of urbanization.

One of the main consequences of climate change are heavy rains. The canopy of trees can absorb about 11.1% of annual rainfall. As a result, this percentage varies focusing on the type of trees used, the time of year and the duration and intensity of rainfall; higher interception rates occur for broadleaf evergreens, warm summer storms, and short, light rain. Tall trees will help to reduce peak rainfalls, with the consequence of stopping and evaporating the water, mitigating light rains and minimizing heavy rains. Therefore, evergreens assist to mitigate surface and water heating.

In addition, a common practice in car parks and large paved surface areas, in general, is to evacuate the rainwater as quickly as possible through the drainage system by pouring that water into a nearby stream. What seems the logical use of these facilities results in a huge amount of water pouring from these canals when the rains are very strong, quickly eroding the stream bed, dragging the vegetation and existing debris of its banks, and leaving a wide rocky watercourse. It is much efficient to produce an on-site water detention system that is able to encourage a progressive evacuation of the water, avoid water runoff and promote a constant influx of water into aquifers. Parking areas also highly contribute to the heat island effect, which happens in asphalt surfaces that do not consider any vegetation, making these surfaces 20º to 40º warmer than a vegetated one, reaching a variation of 48.8 degrees to 17.2 º

The aim of this article is to highlight the vital importance that a correct design of our public realm can have on the adaptation of our cities to climate change and the mitigation of its effects. Acting on small areas of the urban surface with good practice bases, we can create larger networks that minimize the effects of an uncontrolled urbanization. We should imagine a new ecological network to which all public spaces contribute effectively to, considering these not as isolated actions but as a continuous system, achieving a considerable improvement of our urban environment and working to counteract the effects of climate change.

Through an inductive methodology, we will analyze different cases that in recent decades have worked on these issues in order to develop a new code of good practices.