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Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States
Citation:
Barnhart, B., P. Pettus, J. Halama, Bob McKane, P. Mayer, K. Djang, A. Brookes, AND M. Moskal. Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States. JOURNAL OF ENVIRONMENTAL MANAGEMENT. Elsevier Science Ltd, New York, NY, 277:111418, (2021). https://doi.org/10.1016/j.jenvman.2020.111418
Impact/Purpose:
This modeling work demonstrates the impacts of large-scale adoption of green roofs in the Seattle metropolitan area. The results are intended to be used by stakeholders to estimate upper bounds of possible runoff reduction strategies using green roof technologies. This work stems from work supported by an EPA R-authority post doc and was designed to inform resource managers addressing stormwater pollution issues in the Puget Sound. This study was designed with input from Region 10 and builds upon a body of research generated by the VELMA modeling team at PESD supporting multiple tasks delineated in SSWR in research area 10 regarding stormwater management. z
Description:
Green roofs are among the most popular type of green infrastructure implemented in highly urbanized watersheds due to their low cost and efficient utilization of unused or under-used space. However, few studies have evaluated the performance of large-scale adoption of green roofs across entire watersheds. Therefore, in this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area. We utilized a spatially explicit ecohydrological watershed model called Visualizing Ecosystem Land Management Assessments (VELMA) to simulate the resulting stormwater hydrology of implementing green roofs over 25%, 50%, 75%, and 100% of existing buildings within four urban watersheds in Seattle, Washington, United States. We simulated the effects of two types of green roofs: extensive green roofs, which are characterized by shallow soil profiles and short vegetative cover, and intensive green roofs, which are characterized by deeper soil profiles and can support larger vegetation. While buildings only comprise approximately 10% of the total area within each of these watersheds, our simulations showed that 100% implementation of green roofs on these buildings can achieve approximately 10-15% and 20-25% mean annual runoff reductions for extensive and intensive green roofs, respectively, over a 28-year simulation. These results provide an upper limit for volume reductions achievable by green roofs in these urban watersheds. We also showed that stormwater runoff reductions are proportionately smaller during higher flow regimes caused by increased precipitation, likely due to the limited storage capacity of saturated green roofs. In general, green roofs can be effective at reducing stormwater runoff, and their effectiveness is limited by both their areal extent and storage capacity. Our results showed that green roof implementation can be an effective stormwater management tool in highly urban areas, and we demonstrated that our modeling approach can be used to assess the watershed-scale hydrologic impacts of the widespread adoption of green roofs across large metropolitan areas.
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DOI: Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States