Green Water from Green Roofs—The Ecological and Economic Effects

Abstract

Green roofs (GRs) have been one of the most popular solutions for water harvesting in urban areas. Apart from their water retention role and increasing biodiversity, they constitute the missing link between the built and the natural environment, which is required for sustainable human living in cities. This paper aims to calculate the ecological (EE) and economic effect (EcE) of water harvesting via GRs, by contrasting with a traditional roof, and to perform an economic analysis of the social cost benefits that GRs generate during their life cycle, using the Net Present Value (NPV) method. All the calculations and analyses were conducted for both intensive and extensive GRs in 11 of the largest municipalities in Poland, with a population of >250,000 inhabitants. According to the results of this study, water retention and the economic and ecological effects of GRs are highest in the municipalities with the highest assumed number of GRs (Warsaw, Krakow, Wroclaw, and Szczecin). The average EE and EcE equals 507,000 m3/yr and 621,000 USD/yr. The NPV results show that the effectiveness of investments in intensive GRs is, to a certain extent, more significant than in extensive GRs and the average equals 60.77 and 4.47 USD/yr for intensive and extensive GRs, respectively. The results could serve as a reference for the evaluation and optimization of the energy efficiency of rainwater harvesting schemes, in European cities.

Stormwater Management in the City of Warsaw: A Review and Evaluation of Technical Solutions and Strategies to Improve the Capacity of the Combined Sewer System

“…The knowledge is very fragmented and scattered. Only a few papers by different authors contain topics on this issue [69][70][71][72]. However, some sources suggest that Warsaw is not a leader in promoting this type of solution [73].…”

“…In the context of specific scientific work, mention should be made, for example, of the study by Bus and Szel ągowska [72], who presented concrete calculations of the ecological and economic benefits of water retention by green roofs and carried out an analysis of the social-cost benefits for the entire life-cycle of green roofs. Their results showed that water retention and measurable environmental and economic benefits are the highest in cities such as Warsaw, Kraków and Wrocław, as these cities have the highest number of green roofs.…”

Growing of the Cretan Therapeutic Herb Origanum Dictamnus in The Urban Fabric: The Effect of Substrate and Cultivation Site on Plant Growth and Potential Toxic Element Accumulation

“…In the case of the utilization of roofs, the benefits multiply, with the multiple services of green roofs to the sustainability of the urban environment, such as storm water management, reduction of urban heat island effects, noise reduction, and building temperature regulation, as well as connection between the built and the natural environment and direct contact of building occupants with the green roof with social and educational benefits [ 17 , 18 , 19 , 20 ].…”

Development of an Integrated Design Strategy for Blue-Green Architecture

“…Water treatment, water storage and retention areas are more efficient and economical on a larger scale [11,26,27]. Green roofs also become more economically and ecologically cost-effective in terms of rainwater management if they are implemented comprehensively [28]. In context of water flows, industrial processes, which often have significant water consumption, should also be considered [29].…”