Phosphate Leaching from Green Roof Substrates—Can Green Roofs Pollute Urban Water Bodies?

Sustainability addresses the need to reduce the structure’s impact on the environment but does not reduce the environment’s impact on the structure. To explore this relationship, this study focuses on quantifying the impact of green roofs or vegetated roofs on seismic responses such as story displacements, interstory drifts, and floor level accelerations. Using an archetype three-story steel moment frame, nonlinear time history analyses are conducted in OpenSees for a shallow and deep green roof using a suite of ground motions from various distances from the fault to identify key trends and sensitivities in response.

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Addressing the Water–Energy–Food Nexus through Enhanced Green Roof Performance

Sustainability ◽

10.3390/su13041972 ◽

2021 ◽

Vol 13 (4) ◽

pp. 1972

Author(s):

Jeremy Wright ◽

Jeremy Lytle ◽

Devon Santillo ◽

Luzalen Marcos ◽

Kristiina Valter Mai

Keyword(s):

Climate Change ◽

Performance Optimization ◽

Urban Areas ◽

Stormwater Management ◽

Green Roof ◽

Green Roofs ◽

Management Tool ◽

Contributing Factors ◽

Rainwater Runoff ◽

Rain Events

Urban densification and climate change are creating a multitude of issues for cities around the globe. Contributing factors include increased impervious surfaces that result in poor stormwater management, rising urban temperatures, poor air quality, and a lack of available green space. In the context of volatile weather, there are growing concerns regarding the effects of increased intense rainfalls and how they affect highly populated areas. Green roofs are becoming a stormwater management tool, occupying a growing area of urban roof space in many developed cities. In addition to the water-centric approach to the implementation of green roofs, these systems offer a multitude of benefits across the urban water–energy–food nexus. This paper provides insight to green roof systems available that can be utilized as tools to mitigate the effects of climate change in urbanized areas. A new array of green roof testing modules is presented along with research methods employed to address current issues related to food, energy and water performance optimization. Rainwater runoff after three rain events was observed to be reduced commensurate with the presence of a blue roof retention membrane in the testbed, the growing media depth and type, as well as the productive nature of the plants in the testbed. Preliminary observations indicate that more productive green roof systems may have increasingly positive benefits across the water–energy–food nexus in dense urban areas that are vulnerable to climate disruption.

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Hydrologic Performance of an Extensive Green Roof under Intensive Rain Events: Results from a Rain-Chamber Simulation

Sustainability ◽

10.3390/su13063078 ◽

2021 ◽

Vol 13 (6) ◽

pp. 3078

Author(s):

Elena Giacomello ◽

Jacopo Gaspari

Keyword(s):

Water Retention ◽

Green Roof ◽

Green Roofs ◽

International Standards ◽

Dimensionless Number ◽

Runoff Coefficient ◽

Retention Performance ◽

Extensive Green Roof ◽

Rain Events ◽

Hydrologic Performance

The water storage capacity of a green roof generates several benefits for the building conterminous environment. The hydrologic performance is conventionally expressed by the runoff coefficient, according to international standards and guidelines. The runoff coefficient is a dimensionless number and defines the water retention performance over a long period. At the scale of single rain events, characterized by varying intensity and duration, the reaction of the green roof is scarcely investigated. The purpose of this study is to highlight how an extensive green roof—having a supposed minimum water performance, compared to an intensive one—responds to real and repetitive rain events, simulated in a rain chamber with controlled rain and runoff data. The experiment provides, through cumulative curve graphs, the behavior of the green roof sample during four rainy days. The simulated rain events are based on a statistical study (summarized in the paper) of 25 years of rain data for a specific location in North Italy characterized by an average rain/year of 1100 mm. The results prove the active response of the substrate, although thin and mineral, and quick draining, in terms of water retention and detention during intense rain events. The study raises questions about how to better express the water performance of green roofs.

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Influence of Temperature and Moisture Content on Thermal Performance of Green Roof Media

Energies ◽

10.3390/en14092421 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2421

Author(s):

Bohan Shao ◽

Caterina Valeo ◽

Phalguni Mukhopadhyaya ◽

Jianxun He

Keyword(s):

Thermal Conductivity ◽

Moisture Content ◽

Green Roof ◽

Green Roofs ◽

Power Functions ◽

Thick Substrate ◽

Different Temperatures ◽

Test Cells ◽

Substrate Moisture ◽

Phase Transition Zone

The influence of moisture content on substrate thermal conductivity at different temperatures was investigated for four different commercially available substrates for green roofs. In the unfrozen state, as moisture content increased, thermal conductivity increased linearly. In the phase transition zone between +5 and −10 °C, as temperature decreased, thermal conductivity increased sharply during the transition from water to ice. When the substrate was frozen, thermal conductivity varied exponentially with substrate moisture content prior to freezing. Power functions were found between thermal conductivity and temperature. Two equally sized, green roof test cells were constructed and tested to compare various roof configurations including a bare roof, varying media thickness for a green roof, and vegetation. The results show that compared with the bare roof, there is a 75% reduction in the interior temperature’s amplitude for the green roof with 150 mm thick substrate. When a sedum mat was added, there was a 20% reduction in the amplitude of the inner temperature as compared with the cell without a sedum mat.

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Green roof hydrologic performance and modeling: a review

Water Science & Technology ◽

10.2166/wst.2013.770 ◽

2013 ◽

Vol 69 (4) ◽

pp. 727-738 ◽

Cited By ~ 77

Author(s):

Yanling Li ◽

Roger W. Babcock

Keyword(s):

Peak Flow ◽

Green Roof ◽

Field Measurements ◽

Green Roofs ◽

Economic Benefits ◽

Design Parameters ◽

Technical Literature ◽

Factors Affecting ◽

Model Soil ◽

Runoff Volume

Green roofs reduce runoff from impervious surfaces in urban development. This paper reviews the technical literature on green roof hydrology. Laboratory experiments and field measurements have shown that green roofs can reduce stormwater runoff volume by 30 to 86%, reduce peak flow rate by 22 to 93% and delay the peak flow by 0 to 30 min and thereby decrease pollution, flooding and erosion during precipitation events. However, the effectiveness can vary substantially due to design characteristics making performance predictions difficult. Evaluation of the most recently published study findings indicates that the major factors affecting green roof hydrology are precipitation volume, precipitation dynamics, antecedent conditions, growth medium, plant species, and roof slope. This paper also evaluates the computer models commonly used to simulate hydrologic processes for green roofs, including stormwater management model, soil water atmosphere and plant, SWMS-2D, HYDRUS, and other models that are shown to be effective for predicting precipitation response and economic benefits. The review findings indicate that green roofs are effective for reduction of runoff volume and peak flow, and delay of peak flow, however, no tool or model is available to predict expected performance for any given anticipated system based on design parameters that directly affect green roof hydrology.

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A Machine Learning Approach for Estimating the Trophic State of Urban Waters Based on Remote Sensing and Environmental Factors

Remote Sensing ◽

10.3390/rs13132498 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2498

Author(s):

Shijie Zhu ◽

Jingqiao Mao

Keyword(s):

Remote Sensing ◽

Environmental Factors ◽

Water Temperature ◽

Trophic State ◽

Trophic Levels ◽

Water Bodies ◽

Trophic State Index ◽

Urban Water ◽

Estimation Model ◽

Input Variables

To improve the accuracy of remotely sensed estimates of the trophic state index (TSI) of inland urban water bodies, key environmental factors (water temperature and wind field) were considered during the modelling process. Such environmental factors can be easily measured and display a strong correlation with TSI. Then, a backpropagation neural network (BP-NN) was applied to develop the TSI estimation model using remote sensing and environmental factors. The model was trained and validated using the TSI quantified by five water trophic indicators obtained for the period between 2018 and 2019, and then we selected the most appropriate combination of input variables according to the performance of the BP-NN. Our results demonstrate that the optimal performance can be obtained by combining the water temperature and single-band reflection values of Sentinel-2 satellite imagery as input variables (R2 = 0.922, RMSE = 3.256, MAPE = 2.494%, and classification accuracy rate = 86.364%). Finally, the spatial and temporal distribution of the aquatic trophic state over four months with different trophic levels was mapped in Gongqingcheng City using the TSI estimation model. In general, the predictive maps based on our proposed model show significant seasonal changes and spatial characteristics in the water trophic state, indicating the possibility of performing cost-effective, RS-based TSI estimation studies on complex urban water bodies elsewhere.

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A laboratory study to determine the use of polluted river sediment as a substrate for extensive green roofs

Water Science & Technology ◽

10.2166/wst.2018.501 ◽

2018 ◽

Vol 78 (11) ◽

pp. 2247-2255 ◽

Cited By ~ 1

Author(s):

Wei Zhang ◽

Xing Zhong ◽

Wu Che ◽

Huichao Sun ◽

Hailong Zhang

Keyword(s):

River Sediment ◽

Peat Soil ◽

River Sediments ◽

Green Roof ◽

Oxygen Demand ◽

Green Roofs ◽

Polluted River ◽

Artificial Rainfall ◽

Study Laboratory ◽

Extensive Green Roofs

Abstract In this study, laboratory-scale green (e.g. living) roof platforms were established to assess the potential use of polluted river sediment in their substrate mixture. The mean runoff retention of the green roof platforms, which contained peat and/or river sediment, after 11 artificial rainfall events was >72%, significantly higher than traditional roofs. However, green roof platforms that had been filled with peat soil showed chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) leaching. Green roofs that had used river sediment showed good leaching control for COD, TN and TP. The cumulative leaching masses from the green roofs contained 30% (COD), 42% (TN) and 47% (TP) as much as the total leaching mass from traditional roofs, and the Cu, Zn, Cd and Pb leaching risk from green roofs when river sediments are used as part of a substrate mixture was relatively low. Despite some nutrient leaching in the initial phase of runoff from the green roofs, river sediment has the potential to be used as a substrate for extensive green roofs.

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Evaporation from (Blue-)Green Roofs: Assessing the Benefits of a Storage and Capillary Irrigation System Based on Measurements and Modeling

Water ◽

10.3390/w10091253 ◽

2018 ◽

Vol 10 (9) ◽

pp. 1253 ◽

Cited By ~ 4

Author(s):

Dirk Cirkel ◽

Bernard Voortman ◽

Thijs van Veen ◽

Ruud Bartholomeus

Keyword(s):

Energy Balance ◽

Urban Areas ◽

Evaporation Rate ◽

Climate Adaptation ◽

Irrigation System ◽

Green Roof ◽

Green Roofs ◽

C3 Plants ◽

Rapid Decline ◽

Air Temperatures

Worldwide cities are facing increasing temperatures due to climate change and increasing urban density. Green roofs are promoted as a climate adaptation measure to lower air temperatures and improve comfort in urban areas, especially during intensive dry and warm spells. However, there is much debate on the effectiveness of this measure, because of a lack of fundamental knowledge about evaporation from different green roof systems. In this study, we investigate the water and energy balance of different roof types on a rooftop in Amsterdam, the Netherlands. Based on lysimeter measurements and modeling, we compared the water and energy balance of a conventional green roof with blue-green roofs equipped with a novel storage and capillary irrigation system. The roofs were covered either with Sedum or by grasses and herbs. Our measurements and modeling showed that conventional green roof systems (i.e., a Sedum cover and a few centimeters of substrate) have a low evaporation rate and due to a rapid decline in available moisture, a minor cooling effect. Roofs equipped with a storage and capillary irrigation system showed a remarkably large evaporation rate for Sedum species behaving as C3 plants during hot, dry periods. Covered with grasses and herbs, the evaporation rate was even larger. Precipitation storage and capillary irrigation strongly reduced the number of days with dry-out events. Implementing these systems therefore could lead to better cooling efficiencies in cities.

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Vegetation Cover Drives Arthropod Communities in Mediterranean/Subtropical Green Roof Habitats

Sustainability ◽

10.3390/su10114209 ◽

2018 ◽

Vol 10 (11) ◽

pp. 4209 ◽

Cited By ~ 3

Author(s):

Ibrahim Salman ◽

Leon Blaustein

Keyword(s):

Vegetation Cover ◽

Urban Areas ◽

Green Roof ◽

Structural Complexity ◽

Green Roofs ◽

Life Forms ◽

Suitable Habitat ◽

Positive Effects ◽

Habitat Template ◽

Arthropod Abundance

Worldwide, urban areas are expanding both in size and number, which results in a decline in habitats suitable for urban flora and fauna. The construction of urban green features, such as green roofs, may provide suitable habitat patches for many species in urban areas. On green roofs, two approaches have been used to select plants—i.e., matching similar habitat to green roofs (habitat template approach) or identifying plants with suitable traits (plant trait approach). While both approaches may result in suitable habitats for arthropods, how arthropods respond to different combinations of plants is an open question. The aim of this study was to investigate how the structural complexity of different plant forms can affect the abundance and richness of arthropods on green roofs. The experimental design crossed the presence and absence of annuals with three Sedum sediforme (Jacq.) Pau (common name: stonecrops) treatments—i.e., uniformly disrupted Sedum, clumped disrupted Sedum, and no Sedum. We hypothesized that an increased structural diversity due to the coexistence of different life forms of plants on roofs is positively related to the abundance and richness of arthropods. We found that arthropod abundance and richness were positively associated with the percent of vegetation cover and negatively associated with substrate temperature. Neither arthropod abundance nor richness was influenced by the relative moisture of substrate. We also found that arthropod abundance and richness varied by green roof setups (treatments) and by seasonality. Arthropod abundance on green roofs was the highest in treatments with annuals only, while species richness was slightly similar between treatments containing annuals but varied between sampling periods. This study suggests that adding annuals to traditional Sedum roofs has positive effects on arthropods. This finding can support the development of biodiverse cities because most extensive green roofs are inaccessible to the public and can provide undisturbed habitat for several plant and arthropod species.

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