Calculation of the ecological and economic effect of collecting rainwater with «green» roofs

Abstract

The problem of the availability of fresh water on the planet is substantiated and the main concepts of sustainable rainwater management, such as: "SuDS", "BMP", "LID", "GI", as well as the concept of "green" structures, are analyzed. The classification and characteristics of the main types of «green» roofs, as well as their main ecological advantages, are presented. The global market for green roofs is shown growing from USD 1.4 billion in 2020 to a CAGR of 17% from 2020 to 2027, to reach USD 4.2 billion by 2027, and is projected to the extensive type will account for more than half of the total market share. The problem of high costs for installation and maintenance of environmentally friendly solutions for the roof is highlighted, therefore the aim of the work is to calculate the ecological and economic effect of collecting rainwater obtained from "green" roofs, in contrast to traditional roofs, and to conduct an economic analysis of social and cost benefits. what green roofs generate over their life cycle using the Net Present Value (NPV) method. The ecological and economic effect of collecting rainwater with "green" roofs was calculated for four cities of Ukraine: Kyiv, Kharkiv, Dnipro and Lviv. According to the results of calculations, the ecological effect of EE ranges from 394,000 m3 in the city of Dnipro and 450,000 m3 in Kharkiv to 567,000 m3 in Kyiv and 647,000 m3 in Lviv. The difference in the obtained calculations depends primarily on the selected area of "green" roofs, which was the lowest in the city of Dnipro (1.47 million m2) and the highest in the city of Kyiv (2.50 million m2), the values of which were chosen conditionally, as well as from the indicator of the average annual amount of precipitation, which is the highest in the city of Lviv (740 mm). The average value of the ecological effect of EE in relation to water retention in the analyzed cities was calculated, which was 515,000 m3. By multiplying EE and water price, the average ECE for these 4 cities was determined to be $380,500. It was concluded that the price of water is a decisive dependent variable in the calculation of ECE. The calculation of the economic analysis of the profitability of investments in "green" roofs corresponding to 1 m2 of intensive and extensive "green" roofs, which was carried out on the basis of the net present value method (NPV). It is shown that investment costs for "green" roofs include the following stages: design of "green" roofs; installation of the "green" roof system; installation of waterproofing; production of substrate for roofs and its installation; selection and planting of plants on the roof; installation of the irrigation system. It is substantiated that both intensive and extensive "green" roofs have a positive indicator of the net present value of NPV. The average NPV per 1 m2 of an intensive "green" roof is more than 10 times higher than the average NPV per 1 m2 of an extensive "green" roof.