Currently, the world is facing resource scarcity as the environmental impacts of human intervention continue to intensify. To facilitate the conservation and recovery of ecosystems and to transform cities into more sustainable, intelligent, regenerative, and resilient environments, the concepts of circularity and nature-based solutions (NbS) are applied. The role of NbS within green infrastructure in urban resilience is recognised, and considerable efforts are being made by the European Commission (EC) to achieve the European sustainability goals. However, it is not fully evidenced, in an integrated way, which are the main NbS implemented in the urban environment and their effects. This article aims to identify the main and most recent NbS applied in urban environments at the European level and to analyse the integration of different measures as an innovative analysis based on real cases. For this purpose, this work presents a literature review of 69 projects implemented in 24 European cities, as well as 8 urban actions and 3 spatial scales of implementation at the district level. Therefore, there is great potential for NbS adoption in buildings and their surroundings, which are still not prioritized, given the lack of effective monitoring of the effects of NbS.

Green roofs (GRs) are becoming a trend in urban areas, favouring thermal performance of buildings, promoting removal of atmospheric pollutants, and possible water collection spots. Rainwater harvesting systems in buildings can also contribute to the management of stormwater runoff reducing flood peaks. These technologies should be enhanced in Mediterranean countries where water scarcity is increasing and the occurrence of extreme events is becoming very significant, as a result of climate change. An extensive pilot GR with three aromatic plant species – Satureja montana, Thymus caespititius and Thymus pseudolanuginosus, designed to study several parameters affecting rainwater runoff, has been in operation for 12 months. Physico-chemical analyses of roof water runoff (turbidity, pH, conductivity, NH₄⁺, NO₃⁻, PO₄³⁻, chemical oxygen demand) have shown that water was of sufficient quality for non-potable uses in buildings, such as toilet flushing. An innovative approach allowed for the development of an expression to predict a ‘monthly runoff coefficient’ of the GR system. This parameter is essential when planning and designing GRs combined with rainwater harvesting systems in Mediterranean climate. This study is a contribution to improving the basis for the design of rainwater harvesting systems in buildings with extensive GRs under Mediterranean climate.

In addition to the possible contributions of buildings to mitigating CO₂ emissions, increased attention is being paid to the potential impacts of climate change on urban environments. According to the United Nations, about 54% of the planet’s population currently lives in cities, but this percentage is expected to rise to 66% in 2050, which reveals the scale of this issue. This paper develops a reflection on the possible contributions of water-related building installations to mitigate emissions and increase urban area adaptation to the effects of climate change. One of the most promising solutions to facing climate change, which is analysed in detail in this paper, is combining rainwater harvesting systems with green roofs. However, in view of developing the necessary engineering projects, there are insufficient existing studies to estimate the parameters to be used in each location given their climate characteristics, particularly the monthly runoff coefficients, which constitute the key parameter for designing these installations in some regions. Some recent standards present generic theoretical values for designing these combined installations, but they are far from reality in some regions, such as the Mediterranean basin. Therefore, based on the data available in Portugal, this paper reports some of the results obtained from research on the values of the monthly runoff coefficients.

It has become evident that, during this century, climate change will continue, affecting all regions of the planet. The expected impacts over the next few decades may differ from region to region, with some areas becoming humid and others drier. In regions such as the Mediterranean basin, the main expected impacts of climate change will be prolonged droughts and an increase in the intensity and frequency of heavy rains. Measures of mitigation and adaptation are particularly important in urban environments, where more than half of the population lives, and rainwater harvesting systems (RWHS) are considered to be a very suitable solution to these problems. However, the published studies have mainly focussed on buildings, with very limited references to the interest of its application in large urban infrastructure. Based on consumption and precipitation data, this article presents a study on the implementation of an RWHS in a large-scale sports infrastructure located in the city of Cascais (Portugal) intended for the practice of tennis, with 12 brick dust fields, some of them covered. The average annual consumption of potable water for watering the tennis courts is 5500 m³, and the results show that the RWHS can reduce this consumption by >50%, in addition to other expected benefits, such as the known effect of these systems in reducing flood peaks in the area.