Ecoroof Runoff Mitigation Comparison by Photosynthetic Pathway in Three Species of Interest
Start Date
3-16-2026 4:00 PM
End Date
3-16-2026 6:00 PM
Abstract
Stormwater management is critical as urban areas expand and impervious surfaces cover more area. Ecoroofs are increasingly deployed to attenuate roof runoff (mean reduction 33–42% in Portland studies) and peak flows (up to 88% in Portland studies). However, few studies have compared plant functional types, or more specifically photosynthetic pathways in ecoroof hydrologic performance, especially as it relates to seasonal rainfall variability. While sedum (a Crassulacean Acid Metabolism or CAM species) is popular for its drought resilience, its nocturnal stomatal opening behavior may limit evapotranspiration driven water loss compared to C3 or C4 photosynthetic species. In this study, nine modular ecoroof trays (4 ft² each; n = 3 replicates) were constructed with a design common to Portland ecoroofs. One species per bed was planted, being C3 idaho fescue (Festuca idahoensis), C4 buffalograss (Bouteloua dactyloides), and CAM white stonecrop (Sedum album), and runoff volumes were recorded beneath each tray using tipping‑bucket rain gauges. These were compared to rainfall inputs from a nearby rain gauge. Preliminary results indicate that C4 species achieved the highest mean runoff reduction (74 %), followed by CAM ( 68%) and C3 (67 %). This showed a large difference between seasons, likely due to differences in active growing season. During storms preceded by >45 hours of dry conditions, C3 and C4 trays showed 100% retention, whereas CAM required 83 hours. Ongoing analysis is assessing seasonal growth effects, temperature influences, and water use efficiency. These findings will inform species selection for ecoroofs in climates with marked wet-dry cycles, maximizing stormwater benefits while ensuring plant survival.
Subjects
Hydrology, Plant ecology, Sustainable development
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Ecoroof Runoff Mitigation Comparison by Photosynthetic Pathway in Three Species of Interest
Stormwater management is critical as urban areas expand and impervious surfaces cover more area. Ecoroofs are increasingly deployed to attenuate roof runoff (mean reduction 33–42% in Portland studies) and peak flows (up to 88% in Portland studies). However, few studies have compared plant functional types, or more specifically photosynthetic pathways in ecoroof hydrologic performance, especially as it relates to seasonal rainfall variability. While sedum (a Crassulacean Acid Metabolism or CAM species) is popular for its drought resilience, its nocturnal stomatal opening behavior may limit evapotranspiration driven water loss compared to C3 or C4 photosynthetic species. In this study, nine modular ecoroof trays (4 ft² each; n = 3 replicates) were constructed with a design common to Portland ecoroofs. One species per bed was planted, being C3 idaho fescue (Festuca idahoensis), C4 buffalograss (Bouteloua dactyloides), and CAM white stonecrop (Sedum album), and runoff volumes were recorded beneath each tray using tipping‑bucket rain gauges. These were compared to rainfall inputs from a nearby rain gauge. Preliminary results indicate that C4 species achieved the highest mean runoff reduction (74 %), followed by CAM ( 68%) and C3 (67 %). This showed a large difference between seasons, likely due to differences in active growing season. During storms preceded by >45 hours of dry conditions, C3 and C4 trays showed 100% retention, whereas CAM required 83 hours. Ongoing analysis is assessing seasonal growth effects, temperature influences, and water use efficiency. These findings will inform species selection for ecoroofs in climates with marked wet-dry cycles, maximizing stormwater benefits while ensuring plant survival.