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===Water Balance===

===Water Balance===

Green roofs are primarily a practice used to partially achieve water balance and erosion control objectives through interception and [[Evapotranspiration| evapotranspiration]] of precipitation.  The key hydrologic benefit which green roofs have over other forms of LID is the proportion of the water returned to the atmosphere through [[Evapotranspiration| evapotranspiration]].

Green roofs are primarily a practice used to partially achieve water balance and erosion control objectives through interception and [[Evapotranspiration| evapotranspiration]] of precipitation that falls on the roof.  The key hydrologic benefit which green roofs have over other forms of LID is the proportion of the water returned to the atmosphere through [[Evapotranspiration| evapotranspiration]]. Considerable research has been conducted in recent years to define the runoff reduction or water retention capacity of extensive green roofs in climates similar to those that occur in Ontario and Canada.

* Controlled studies have indicated that maturing green roofs may have improved water retention properties <ref>De-Ville, S., Menon, M., Jia, X., Reed, G., Stovin, V. 2017. The impact of green roof ageing on substrate characteristics and hydrological performance. Journal of Hydrology. Volume 547. pp 332-344. https://doi.org/10.1016/j.jhydrol.2017.02.006.</ref>.  

* Controlled studies have indicated that maturing green roofs may have improved water retention properties <ref>De-Ville, S., Menon, M., Jia, X., Reed, G., Stovin, V. 2017. The impact of green roof ageing on substrate characteristics and hydrological performance. Journal of Hydrology. Volume 547. pp 332-344. https://doi.org/10.1016/j.jhydrol.2017.02.006.</ref>.