Contribution of urban green infrastructure to stormwater management and a more efficient urban water use

Stormwater management in urban areas is a critical issue that must be carefully addressed in urban planning, given the current scenario of climate change and the increase of highly impermeable surfaces. In some climates, such as the Mediterranean, extreme precipitation events that occur in short periods of time (with significant economic losses associated), alternating with prolonged periods of drought, are becoming frequent, posing several challenges to decision makers and city planners. In addition to the effect of climate change, the availability of good water quality in many urban areas is decreasing due to economic growth, population development and/or pollution. However, large volumes of drinking water are consumed in cities for non-potable uses, such as garden watering, flushing toilets or washing cars or pavements, for example. For these reasons, it is imperative to rethink the water paradigm in urban areas, integrating stormwater management with public supply management and urban green infrastructure (or Nature-based Solutions – NbS). There are several NbS that can be implemented in urban areas, some at street level (e.g. permeable pavements, rain gardens) and others at building level (green roofs and green walls), the latter with the advantage of not occupying urban land and to utilize an impermeable area that is generally unused. These NbS contribute to stormwater management through infiltration or a temporary retention of stormwater, delaying runoff into urban drainage systems. Besides that, some of these NbS can be combined with solutions for using water for non-potable purposes in buildings, as is the case, for example, of the combination of green roofs with rainwater harvesting systems, which increases the potential for managing taking advantage of the contribution of each of these constructive solutions. The saving in potable water can also have advantages in face to the water-energy nexus, reducing energy needs to abstract, treat and transport water to the cities and buildings. This article refers two case studies carried out in Portugal, a Mediterranean country that is expected to be heavily affected by climate change, within the scope of the contribution of urban green infrastructures and the management of stormwater to a more efficient urban water use. Conclusions show that implementing NbS in urban areas brings several benefits that should be valued. With the continuous and growing number of successful case studies in different regions, better evidence will be proposed to support its implementation. The interrelationship between green (and blue) urban infrastructures, stormwater and urban water systems will certainly take place in the future within the scope of Urban Water Communities (UWC), a concept similar to Renewable Energy Communities (REC), created in Europe in 2019, to better manage the disparities between the demand and supply of renewable energy, promoting its production. Within the scope of a UWC, residential, public, commercial, service buildings, etc., with rainwater collection, water reuse, etc., will be able to optimize the use of water and share any excess resources with neighbouring buildings or with blue or green local infrastructures, increasing sustainability and resilience to climate change in urban environments.