Green roofs for stormwater runoff retention: A global quantitative synthesis of the performance

Xinzhu Zheng,Yicheng Zou,Amanda W Lounsbury,Can Wang,Ranran Wang

doi:10.1016/j.resconrec.2021.105577

Abstract

The global popularity of green roofs (GRs) rises as urban runoff becomes a primary environmental concern in both developed and developing countries. Although a growing number of studies have measured the runoff retention (RR) performance of GRs and investigated the underpinning factors, a systematic and quantitative understanding is lacking. This study applies a statistical approach on a dataset of 2375 original experimental samples associated with the RR performance of GRs observed across 21 countries, consolidated from 75 internationally peer-reviewed studies published in 2005–2020. The results show that the sampled RR rates (i.e., the proportion of rainfall retained on a per-event basis) range widely (0–100%), with an average of 62%. Rainfall intensity, substrate depth, GR surface coverage, climate type, vegetation type, and season type partially explain the variances in retention performance. Moreover, the effects of some factors (e.g., rainfall intensity) are not isolated but contingent on other factors (e.g., vegetative cover). This global synthesis shows few samples emanate from Africa, Central America, and Central Asia, highlighting the need of more GR research and applications in these regions. The average GR RR rate appears lower than some specified in green building standards, which implies the need to further improve the RR performance of GRs or combine GRs with other RR measures. Contingent effects of GR RR incluencing factors demonstrate the need to leverage design parameters and to account for local weather and climate characteristics in the optimization of GR performance.

Highlights

The world has observed rapid urbanization over the past decades, with increased construction to accommodate the shift in population from rural to urban areas (Zhou et al, 2020)
Of the 75 studies (N = 75) and the 2375 experimental samples (n = 2375) investigating the runoff mitigation relationships of green roofs (GRs), OECD countries comprised more than 70% of the data (N = 56, n = 1661). 31 studies and 1028 samples were obtained from OECD-Europe while 25 studies and 633 samples were from non-European OECD countries, of which the majority came from the United States (N = 14, n = 230). 16 studies and 574 samples were conducted in developing countries in Asia, predominantly China (N = 13, n = 481)
Applying a statistical approach on the dataset, we systematically and consistently quantify the GR runoff retention (RR) effect of main factors identified in prior studies: rainfall intensity, GR substrate depth, GR surface coverage, climate type, GR vegetation types and season types on RR performance

Summary

Introduction

The world has observed rapid urbanization over the past decades, with increased construction to accommodate the shift in population from rural to urban areas (Zhou et al, 2020). Given that buildings can occupy 50% or more of a city’s surface area (Dunnett and Kingsbury, 2008), green roofs (GRs) have a high exploit ative potential (Kelly et al, 2020) to tackle the multiple threats imposed by urbanization and climate change (Akther et al, 2018) and fulfill the SDGs. GRs are an extension of an existing roof that allows for the propagation of rooftop vegetation (the vegetation layer) on top of a growing media (the substrate layer) over a waterproofing membrane (Vijayaraghavan, 2016). GRs are a low-impact development (LID) measure that mimics natural processes to manage stormwater without occupying any addi tional urban land (Zhang et al, 2015; Buccola and Spolek, 2011)

Methods

Results

Discussion

Conclusion