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• Unit area runoff decreases slightly with the increase of roof area but this effect is not statistically significant. • Plant richness and substrate type did not affect the runoff from the GRs. • Substrate depth was the only structural factor which demonstrated a statistically significant effect on the runoff per unit area. • No interactions between the four factors that affect the hydrological process of GRs were statistically significant. Green Roofs (GRs) are a type of Blue Green Infrastructure, growing in popularity due to their ability to provide numerous benefits. Designers and modelers of GRs typically make the assumption that GRs are homogeneous, which means that for different roof areas and the same structural factors such as substrate depth and composition, they have the same runoff per unit area. Based on this assumption, the measured data from small scale GRs in the laboratory can be applied to large GRs in the field. However, this assumption of homogeneity has not been sufficiently verified. To investigate this gap, an outdoor experiment was carried out from April 25 to December 1, 2021. Thirty-six GRs were constructed following an orthogonal experimental design with four primary structural factors investigated (i.e., substrate type (ST), substrate depth (SD), plant richness (PR), and roof area (RA)). Rain and runoff data were recorded and N -way ANOVA was used to evaluate the impact of the structural factors. Results showed that there were no statistically significant interactions between the structural factors that affected the GR runoff. The order of influence of the individual parameters, determined by the F value statistical metric was: SD > RA > ST > PR. However, substrate depth was the only structural factor which significantly affected the runoff per unit area of GR. Plant richness and substrate types showed no statistically significant effect on the GR runoff. The results of this study indicate that the implicit assumption: GRs are homogeneous, is acceptable. [ABSTRACT FROM AUTHOR]

Significant management needs raised in urban sewer system to facilitate urban resilience to rainstorm. The work investigated the effects of temporal evolution of rainfall on hydrograph and pollutant discharge of CSO over an intensive observation period of 12 months, with special attention to differences in temporal scale for supporting management decision making. The characteristics of rainfall in different temporal scales helped overflow-risk identification and assessment. Prolonged dry seasons over 112 days in the CSO monitored year 2018 increased the sediment buildup in the pipes. The built sediment was mostly flushed out to overflow (and the treatment facility) by initial rainfall during 47 h. Following CSO hydraulics and pollutant discharge follows initial peak patterns which responded to rainfall patterns. Results of Redundancy analysis and network analysis showed that the combined effects of rainfall, urbanization, and sediments as "CSO troika" are the driving forces for CSO pollutants in the long-term. The improved characterization of CSO events and the associated pollutants has refined our understanding of how overflow hydrograph and pollutant discharge responds to rainfall temporally, which methodology supported decision making in the combining source/process control with terminal management for facilizing urban resilience. [Display omitted] • The sophisticated investigation of CSOs supported decision making by methodology. • Rainfall pattern and sewer sediment together shaped overflow pollutants. • Combined sewer sediments were built-up in dry season and flushed out in wet season. • Overflow pollutants SS, COD, and TN follows peak-sustain pattern similar with rain. • Temporal evolution of CSOs' hydrograph and pollutants discharge were investigated. [ABSTRACT FROM AUTHOR]