Cost effects of green roof implementation on water management within the Netherlands

Abstract

Rainfall intensity and duration have increased over the last century within the Netherlands, and are predicted to grow further in the future. In order to combat the expected rise in urban flooding within Utrecht, this paper reviews the function of green roofs as a water management tool to establish their utility within the city, and by extension, other Dutch cities which are soon to face the same issue. Using GIS software and a literature review of previous works, this paper answers the questions of (1) how large of an area can be green roofed within Utrecht (2) what is the ideal green roof design for storm water management, and how much rain can it retain and (3) what are the costs and financial benefits of this project if green roofs were to be installed city-wide on all eligible green roofs. It was determined that 7,660,615.43 m2 or 69% of roof tops would be eligible for green roof installations. These installations would be capable of retaining 83.5% of all rainfall under heavy precipitation conditions if built as intensive systems. In order to bring a project of such a large magnitude to fruition, an initial investment of €3.5 billion would be necessary for installation, while an additional yearly maintenance of €46 million would be needed. Yearly benefits of the project were found to be around €500 million, meaning that the return on investment would be roughly 14 years, after which the systems would continue to reap benefits for the city for an estimated 26 years. Given the environmental and financial benefits this project can offer the city of Utrecht, its adoption should be considered by the parties responsible for water management within the area.