Changes

*Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modelled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.

*Daily irrigation can reduce the annual retention by 20% compared to a roof without irrigation (i.e., 40% for irrigated compared to 60% without irrigation)<ref name=Hill/>. However, recirculating rainwater from a cistern was estimated to double the annual retention in Florida<ref>Hardin, M.; Wanielista, M.; Chopra, M. 2012. A Mass Balance Model for Designing Green Roof Systems that Incorporate a Cistern for Re-Use. Water, 4, 914-931. http://www.mdpi.com/2073-4441/4/4/914</ref>. The research team modelled 87% retention for a green roof coupled with a cistern, compared to 43% for the green roof alone.

An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>Curve Number and Runoff Coefficients for Extensive Living Roofs

An appropriate NRCS curve number for modelling green roofs without irrigation in Southern Ontario is 90 <ref>

Elizabeth Fassman-Beck, Ph.D., A.M.ASCE; William Hunt, Ph.D., P.E., M.ASCE; Robert Berghage, Ph.D.; Donald Carpenter, Ph.D., P.E., M.ASCE; Timothy Kurtz, P.E., M.ASCE; Virginia Stovin, Ph.D.; and Bridget Wadzuk, Ph.D., A.M.ASCE https://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001318</ref><ref name=Hill/>.

Fassman-Beck, E., Hunt, W., P.E. Robert Berghage, R., Donald Carpenter, D., Kurtz, T., Stovin, V., Wadzuk, B. Curve Number and Runoff Coefficients for Extensive Living Roofs. Journal of Hydrologic Engineering. Vol.21. Issue 3. ASCE. https://ascelibrary.org/doi/abs/10.1061/(ASCE)HE.1943-5584.0001318</ref> <ref name=Hill/>.

In a study to investigate how green roof runoff reduction performance is affected by climate, Talebi et al. (2019) used water balance and evapotranspiration models to simulate runoff produced by green roofs in six Canadian cities (Vancouver, Calgary, Regina, Toronto, London and Halifax).  Results showed that predicted runoff reduction performance varied from 17% to 50% for low water use plants.  The best performance was predicted to occur in Regina and Calgary (drier climates), while the poorest performance was predicted for Halifax and Vancouver (wetter climates).  Average annual runoff reduction was highest in Toronto and London and lowest in Vancouver.<ref>Talebi, A., Bagg, S., Sleep, B.S., O'Carroll, D.M. 2019. Water retention performance of green roof technology: A comparison of Canadian climates. Ecological Engineering, 126, (2019), 1-15. https://www.sciencedirect.com/science/article/abs/pii/S0925857418303835?via%3Dihub</ref>  

In a study to investigate how green roof runoff reduction performance is affected by climate, Talebi et al. (2019) used water balance and evapotranspiration models to simulate runoff produced by green roofs in six Canadian cities (Vancouver, Calgary, Regina, Toronto, London and Halifax).  Results showed that predicted runoff reduction performance varied from 17% to 50% for low water use plants.  The best performance was predicted to occur in Regina and Calgary (drier climates), while the poorest performance was predicted for Halifax and Vancouver (wetter climates).  Average annual runoff reduction was highest in Toronto and London and lowest in Vancouver.<ref>Talebi, A., Bagg, S., Sleep, B.S., O'Carroll, D.M. 2019. Water retention performance of green roof technology: A comparison of Canadian climates. Ecological Engineering, 126, (2019), 1-15. https://www.sciencedirect.com/science/article/abs/pii/S0925857418303835?via%3Dihub</ref>