Hydrological Analysis of Green Roofs Performance under a Mediterranean Climate: A Case Study in Lisbon, Portugal

Abstract

In this paper, the hydrological performance of eight pilot green roofs (GR) installed in Lisbon, Portugal, under a Mediterranean climate is analyzed. The pilot units were installed at Instituto Superior Técnico campus of Lisbon University. The pilots present different plant species and different substrate types, with some of the units incorporating recycled construction and demolition waste (RCW). The green roofs pilots’ hydrologic performance was evaluated through the simulation of artificial precipitation events between March 2021 and July 2021. Considering the results obtained, it can be concluded that the inclusion of RCW in the substrate composition did not hinder the development of vegetation or the hydrological performance of GR. The results showed a rainfall water retention per event ranging from 37% to 100%, with an average rainfall retention of about 81%. The runoff delay ranged from 2 to 18 min, and the peak attenuation ranged from 30 to 100%. The results indicated that previous substrate moisture strongly influences the hydrological performance of GR. As the inclusion of RCW in the substrate composition promotes a more effective drainage of the substrate during dry conditions, it is considered that RCW may have positive impacts on GR’s hydrological performance.

Technical and Financial Feasibility Analysis of Rainwater Harvesting Using Conventional or Green Roofs in an Industrial Building

“…Even so, the available rainwater volume is enough to supply the building's consumption for "other uses", excepting July to September. These results align with data obtained by [64,65] concerning the hydrological performance of GRs under the Mediterranean climate that showed water retention from 37 to 100% and from 12 to 100%, respectively. The reduction in RWHS performance associated with the installation of GR was also reported by [15,45], who claimed that combined systems may reduce RWHS efficiency in low rainfall climates, whereas in higher rainfall climates they may have a positive effect on RWHS efficiency as GR reduces excessive rainwater runoff.…”

Influence of Green Roofs on the Design of a Public Stormwater Drainage System: A Case Study

“…It is a fact that conventional roofs allow rainwater to runoff their surfaces quickly, increasing flooding. GR, on the other hand, are considered to be of greater importance as they absorb rainwater, delaying its runoff and promoting evapotranspiration, increasing the effectiveness of stormwater management [12], as it is also shown in the studies [22,23,31,32]. Despite the urban allotment of only 2.1 ha, with the reduction of the maximum flow rate obtained, the impact of this NBS at the city level could be huge.…”

“…A panoply of experimental studies have demonstrated, in several regions of the world and in different climates, the hydrological performance of GR in terms of control of rainwater runoff, sometimes in comparison with conventional roofs [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Noteworthy are two studies carried out in Lisbon, Portugal, under the Mediterranean climate, where the hydrological performance of GR was analyzed with favorable results in terms of runoff control, highlighting among other parameters, water retention from 37 to 100% in the study of Santos et al [31] and from 12 to 100% in the study of Brandão et al [32].…”

Lisbon Master Plans and Nature-Based Solutions

“…The plan has also considered decentralized blue-green solutions (e.g., stormwater source control techniques), such as the detention ponds of Alto da Ajuda and Ameixoeira, and involved not only physical construction measures, but also non-physical actions, such as knowledge acquisition through research [5], on capacity building, a monitoring and warning system, and public awareness campaigns. As major interventions for flooding control, two stormwater drainage tunnels have been built since 2022, both with 5.5 m diameter that will divert the stormwater flows of important tributaries areas of the main catchments directly to the Tagus River [6]. These tunnels will prevent the city downtown and most of the riverfront from frequent flooding events.…”