Modeling the hydrologic effects of watershed-scale green roof implementation in the Pacific Northwest, United States.

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. In this study, we examined the effectiveness of green roofs to attenuate stormwater runoff across a large metropolitan area in the Pacific Northwest, United States. 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 the four 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.

Barnhart B ，Pettus P ，Halama J ，McKane R ，Mayer P ，Djang K ，Brookes A ，Moskal LM ... -  《-》

Does the spatial location of green roofs affects runoff mitigation in small urbanized catchments?

Green roofs have been treated as practical low impact development (LID) strategies to retain stormwater runoff and alleviate the rainfall-induced flooding risks in urban regions. The purpose of this study was to analyze the hydrological effects of the spatial location of green roofs in urbanized catchments. In the built-up region of Beijing, 12 urbanized catchments with various architectural patterns were chosen as the study areas. To distinguish the spatial characteristics of roof surfaces, we defined the effective roof surfaces to distinguish from other types of roofs, which have more convenient or direct hydrological connections to drainage systems. A hydrological model was then used to simulate the stormwater mitigation performance of green roofs for the study catchments, which were assigned to different rainfall conditions. The simulation results confirmed the benefits of implementing green roofs for urban stormwater regulation. However, the spatial variability of green roofs showed inherent influences on the runoff mitigation capacity in urbanized catchments. Greening on effective roof surfaces would provide more effective stormwater regulation benefits, for reductions in both runoff volume and peak flow. In addition, the spatial arrangement characteristics of roof surfaces also influenced the hydrological efficiency of green roofs. The effect of the spatial location of green roofs on runoff mitigation was rainfall-dependent. These findings provide insights into the hydrological role of green roofs, and suggest that proper siting of LID facilities should be a consideration for urban stormwater management in order to fulfill the hydrological efficiency and cost-effectiveness planning target.

Yao L ，Wu Z ，Wang Y ，Sun S ，Wei W ，Xu Y ... -  《-》

[Comparison on the stormwater runoff effects of roof greening in different urban functional areas].

Ling Z ，Peng L ，Wen H 《-》

Cost-effectiveness analysis of extensive green roofs for urban stormwater control in response to future climate change scenarios.

Green roof, as a popular low impact development practice, has become important to mitigate adverse impacts of future climate change on urban stormwater. However, there is limited information regarding assessment of the effectiveness of green roofs in response to uncertain future climate change challenges. In this study, the validated model was used to simulate the reduction performance of green roofs on urban catchment outflow and assess their cost-effectiveness in response to design storms under climate change scenarios. Results showed that the median runoff volume of urban catchments increased by 12.5 %-14.6 % and 15.5 %-18.1 % and the median peak flow rate increased by 14.4 %-17.8 % and 17.9 %-22.1 % under SSP2-4.5 and SSP5-8.5 scenarios, respectively. This indicated the variability of runoff volume and peak flow changes for short return storm events caused by climate change was relatively high. Green roof implementation had reasonable mitigation effects on runoff volume and peak flow amplification in urban catchments caused by climate change. The median runoff volume reduction of green roofs for the 1-year storm was 15.2 % under SSP2-4.5 scenario. As rainfall intensity increased, the median runoff volume reduction of green roofs significantly declined to 5.6 % for the 100-year storm. However, the variations of runoff volume and peak flow reduction of green roofs were relatively smaller for longer return periods under climate change scenarios. Runoff reduction percentages of green roofs increased linearly with their implementation cost. The average value of the cost-effectiveness (C/E) index for green roofs was 91.2 %/million $ under base climate condition, and it decreased to 88.9 %/million $ and 88.4 %/million $ for SSP2-4.5 and SSP5-8.5 scenarios, respectively. The C/E values decreased with increasing storm return period, and the values were relatively lower in SSP5-8.5 scenarios. These results could help to understand the potential role of green roofs to mitigate the impacts of future climate change.

Liu W ，Feng Q ，Engel BA ，Zhang X ... -  《-》

Improved urban runoff prediction using high-resolution land-use, imperviousness, and stormwater infrastructure data applied to a process-based ecohydrological model.

Halama J ，McKane R ，Barnhart B ，Pettus P ，Brookes A ，Djang K ，Phan V ，Chokshi S ，Graham J ... -  《-》