Peak flow & volume reduction
- Hutchinson D, Abrams P, Retzlaff R and Liptan T (2003). Stormwater monitoring of two ecoroofs in Portland, Oregon, USA. City of Portland, Bureau of Environmental Services.
Retention rate can be up to 100% in summer, and down to 69% at other times of the year. for a 100-150 mm thick green roof, according to a study that monitored stormwater runoff from two ecoroofs in Portland, Oregon. This study also showed that green roofs retained all the rain that fell on them during small to moderate storms. In large rain events, any extra water simply runs off once the substrate water holding capacity was reached.
- Locatelli L, Mark O, Mikkelsen PS, Arnbjerg-Nielsen K, Jensen MB and Binning PJ (2014) Modelling of green roof hydrological performance for urban drainage applications. Journal of Hydrology, 519(D), pp. 3237-3248.
- Voyde E (2009) Quantifying the complete hydrologic budget for an extensive living roof, University of Auckland.
72% of cumulative rainfall volume is retained and 92% of peak flow is reduced by the substrate/layers of a green roof system.
Water quality improvement
- Zhang Z (2019) The role of plants in green roof rainfall retention. School of Ecosystems and Forest Sciences, University of Melbourne.
Green roofs in Melbourne, Australia perform well for retention (average ~73% in total study period; average ~91% in per-event), particularly in warm and dry climates with a large proportion of small rainfall events.
Urban heat reduction
- Coutts AM, Daly E, Beringer J and Tapper NJ (2013) Assessing practical measures to reduce urban heat: Green and cool roofs. Building and Environment, 70, pp. 266-276.
- Razzaghmanesh M and Beecham S (2012) Introducing green roofs into the urban and built environments of Adelaide. TREENET Symposium.
Demonstrates that runoff water quality is suitable for irrigation and non-potable use. The study also shows that an extensive roof is more efficient at removing nitrogen and phosphorus than an intensive (deep) roof.