Factors Controlling the Hydraulic Efficiency of Green Roofs in the Metropolitan Area of Milan (Italy)

Franco Salerno, Lucia Valsecchi, Riccardo Minoia, Diego Copetti, Gianni Tartari, Nicolas Guyennon, Nicola Colombo, Niccolò Pirola, Benedetta Barozzi, Alice Bellazzi and Laura Marziali
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Franco Salerno: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy
Lucia Valsecchi: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy
Riccardo Minoia: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy
Diego Copetti: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy
Gianni Tartari: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy
Nicolas Guyennon: Water Research Institute, National Research Council, IRSA-CNR, 00015 Monterotondo, Italy
Nicola Colombo: Department of Agricultural, Forest and Food Sciences, University of Turin, 10095 Grugliasco, Italy
Niccolò Pirola: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy
Benedetta Barozzi: Construction Technologies Institute, National Research Council, ITC-CNR, 20098 Milan, Italy
Alice Bellazzi: Construction Technologies Institute, National Research Council, ITC-CNR, 20098 Milan, Italy
Laura Marziali: Water Research Institute, National Research Council, IRSA-CNR, 20861 Brugherio, Italy

Sustainability, 2021, vol. 13, issue 24, 1-13

Abstract: Green roofs (GRs) are considered sustainable solutions for the adaptation of urban water management to climate change. The use of GRs is particularly promising in urban environments like the Metropolitan Area of Milan, the most urbanized area in Italy. In this work, we evaluated the subsurface runoff coefficient at the event-time scale, for more than one year of observations, of 68 small-scale test beds comprising different configurations of green roofs (e.g., different vegetations, types and depths of growing media, and different slopes) installed in the Metropolitan Area of Milan. The objectives of this study are three-fold. Firstly, the controlling factors of the hydraulic have been assessed for efficiency. We calculated a mean drainage flow rate of 51%, finding that growing media play a significant role in determining the drainage flow during the spring, at the beginning of the vegetative period. During this season, water retention in fertilized beds increases significantly. At the beginning of the summer, the vegetation cover is able to significantly reduce the drainage flow, playing an even more crucial role with respect to the growing medium material. However, we found that the vegetation type (grass field and Sedum ) does not play a significant role in the retention processes. Secondly, the delay of the peak flow rate was determined. We found a precipitation peak delay from 1 to 2 h, which would be sufficient to guarantee environmental benefits for urban drainage. Finally, the factors controlling the hydraulic efficiency of GRs for individual precipitation events were assessed. We found that soil moisture and cumulated precipitation are both significant factors determining the drainage flow rate. In conclusion, we point out that soil moisture is one of the main parameters characterizing GR drainage and should be further considered in future research efforts devoted to the analysis of GR performance.

Keywords: green roof; peak flow delay; soil moisture; water retention; urban hydrology (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2021
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