Laboratory Tests of Substrate Physical Properties May Not Represent the Retention Capacity of Green Roof Substrates In Situ

Abstract

Green roofs can be used to reduce the volume of polluted stormwater that is generated by cities. Modelling rainfall retention is critical, but green roof water balance models often rely on the physical properties of substrates. In these models, substrate water holding capacity (WHC) determines the depth of water which can be stored before runoff is generated; whereas, the permanent wilting point (PWP) limits evapotranspiration. The WHC and PWP, as well as plant available water (PAW; where PAW = WHC - PWP), as determined from laboratory tests, may not truly reflect how substrates perform on green roofs. We therefore ran a simulated rainfall experiment on green roof modules to (i) compare the ..