Green roof storage capacity can be more important than evapotranspiration for retention performance. (15th February 2019)

• Record Type: Journal Article
• Authors: Zhang, Zheng; Szota, Christopher; Fletcher, Tim D.; Williams, Nicholas S.G.; Farrell, Claire
• Is Part Of: Journal of environmental management. Volume 232(2019)
• Page Start: 404
• Page End: 412
• Publication Date: 2019-02-15
• Subjects: Green roof -- Retention -- ET -- Maximum water content -- Plants water use; Environmental policy -- Periodicals; Environmental management -- Periodicals; Environment -- Periodicals; Ecology -- Periodicals; 363.705
• DOI: 10.1016/j.jenvman.2018.11.070
• Languages: English
• ISSNs: 0301-4797

Abstract

Abstract: Green roofs can significantly reduce stormwater runoff volumes. Plant selection is crucial to retention performance, as it is influenced by how well plants dry out substrates between rainfall events. While the role of plants in evapotranspiration ( ET ) on green roofs is well-studied, their potential influence on retention via their impacts on water movement through substrates is poorly understood. We used a simulated rainfall experiment with plant species with different water use strategies to determine the key drivers of green roof retention performance. Overall per-event retention was very high (89–95%) and similar for all plant species and unplanted modules for small events. However, for larger events, some species showed lower retention than unplanted modules or low-water using succulent species. Despite the fact that these species were more effective at replenishing storage between rainfall events due to their higher ET, they reduced the maximum storage capacity of the substrate, likely due to their root systems creating preferential flow paths. This finding has important implications for green roofs, as although ET represents the primary means by which the storage capacity of green roofs can be regenerated, if species with high ET also reduce the maximum storage capacity, effective retention performance is reduced. Therefore, we suggest that species selection must first focus on how plants affect storage capacity in the first instance and consider water use strategies as a secondary objective. Highlights: We evaluated plant effects on rainfall retention. Rainfall retention depends more on substrate storage capacity than on ET. Some species reduce substrate storage through preferential flow paths. These root-induced preferential flow paths can overwhelm plant ET benefits.