Green Roof Systems Research Articles

Assessment of the long-term hydrological performance of a green roof system in stormwater control

Green roof systems (GRs) are effective tools for urban stormwater management. However, there is limited documentation of the long-term hydrological performance of GRs to support decision-making. This study evaluated long-term field monitoring records (7 years) from a 12-year-old GR, situated in a Moist Subtropical Mid-Latitude Climate, to analyze seasonality in and evolution of hydrological performance. The monitoring system was built within a pan lysimeter buried under substrate layers matching the surrounding GR. The monitoring results highlight the efficacy of this GR in long-term stormwater runoff control. The GR can retain 87% of the annual precipitation and return 54% of the precipitation to the atmosphere through evapotranspiration (ET) and sustain long-term event-based mean runoff volume reductions, peak flow reductions, and flow delays of 82%, 93%, and 4.3 h, respectively. The initial moisture content prior to events was highly correlated with hydrological performance, with a seasonal mean Spearman correlation coefficient of 0.47, suggesting the potential of enhancing ET from the GR to improve performance. Substrate water holding capacity increased over time, but no obvious changes in water retention performance were observed. These monitoring results from the aging GR demonstrate the effectiveness of GR systems for long-term stormwater management.

Comparative Evaluation of Evapotranspiration and Optimization Schemes for Green Roof Runoff Simulations Using HYDRUS-1D

The use of green roofs, a low-impact development practice, can be an effective means of reducing direct runoff in urban centers. Green roof modeling can enable efficient design by preliminarily grasping the behavior of the green roof system according to specific configurations. In this study, we aimed to find appropriate evapotranspiration and parameter optimization schemes for HYDRUS-1D, a commonly used modeling tool for green roofs. Comparative studies of this sort in the context of green roof runoff modeling have not been conducted previously and are important in guiding users to overcome the difficulties of choosing the right numerical schemes for an accurate prediction of runoff from a green roof. As a study site, the Portland Building Ecoroof in Portland, Oregon, USA, was chosen, as green roof configurations and observed data for climate and runoff were available. From the simulation results of the runoff volume, the Blaney–Criddle method, which was considered an alternative, was found to be appropriate for calculating evapotranspiration from a green roof (R2 = 0.82) relative to the Hargreaves method built in HYDRUS-1D (R2 = 0.46). In addition, this study showed that the optimization method using the harmony search algorithm, which was proposed as an alternative optimizer, was better (R2 = 0.95) than that of the HYDRUS-1D’s own optimization module (R2 = 0.82) in calibrating HYDRUS-1D for green roof runoff. The findings are thought to be useful in guiding modelers who are considering using HYDRUS-1D for green roof runoff simulations.

Long-term evaluation of soil-based bioelectrochemical green roof systems for greywater treatment

Water scarcity has generated the need to identify new sources. Due to its low organic contaminant load, greywater reuse has emerged as a potential alternative. Moreover, the search for decentralized treatment systems in urban areas has prompted research on using green roofs for greywater treatment. However, the performance of organic matter removal is limited by the type of substrate and height of the growing media. Bioelectrochemical systems (BESs) improve treatment performance by providing an additional electron acceptor (the electrode). In this study, nine reactors under three different conditions, i.e., open circuit (OC), microbial fuel cell (MFC), and microbial electrolysis cell (MEC), were built to evaluate the treatment of synthetic greywater in a substrate-growing medium composed of perlite and coconut fiber and operated in batch-cycle mode for 397 days. The results suggested that using BESs enables greywater treatment and the removal of pollutants to levels that allow their reuse for irrigation. Furthermore, electrical conductivity was reduced from 732.4 ± 41.2 μS/cm2 in OC to 637.32 ± 22.73 μS/cm2 and 543.15 ± 19.69 μS/cm2 in MEC and MFC, respectively. The soluble chemical oxygen demand in the latter treatments reached 76% removal, compared to levels above the OC, which only reached approximately 67%. Microbial community analysis revealed differences, mainly in the cathodes, showing a higher development of Flavobacterium, Azospirillum, and Zoogloea in MFCs, which could explain the higher levels of organic matter removal in the other conditions, suggesting that the BES could produce an enrichment of beneficial bacterial groups for treatment. Therefore, implementing BESs in green roofs enables sustainable long-term greywater treatment.

The impact of green roofs’ composition on its overall life cycle

Green roof systems have been developed to improve the environmental, economic, and social aspects of sustainability. Selecting the appropriate version of the green roof composition plays an important role in the life cycle assessment of a green roof. In this study, 10 compositions of an intensive green roof for moderate zone and 4 green roof compositions for different climatic conditions were designed and comprehensively assessed in terms of their environmental and economic impacts within the “Cradle-to-Cradle” system boundary. The assessment was carried out over a 50-year period for a moderate climate zone. The results showed that asphalt strips and concrete slab produced the highest total emissions. It was found that most greenhouse gases emissions were released in the operational energy consumption phase and in the production phase. The energy consumption phase (48.78%) for automatic irrigation and maintenance caused the highest Global Warming Potential (GWP) value (758.39 kg CO2e) in the worst variant, which also caused the highest life cycle cost (878.47€). On the contrary, in the best variant, planting more vegetation and lower maintenance and irrigation requirements led to a reduction in GWP (445.0 kg CO2e), but in terms of cost (506.6€) this composition didn't represent the best variant. The Global Warming Potential Biogenic (GWP-bio) compared to the Global Warming Potential Total (GWP-total) represents a proportion ranging from 0.8% to 78% depending on the proposed vegetation. Overall higher biogenic carbon values (up to 1525 kg CO2e) were observed for the proposed tall vegetation of Magnolia, Red Mulberry, Hawthorne, Cherry, and Crab-apple Tree. Based on the results of the multicriteria analysis, which included core environmental & economic parameters, biogenic carbon emission levels, the outcome of this paper proposed optimal green roof composition. Optimal intensive green roof composition was subjected to a sensitivity analysis to determine the impact of changing climatic conditions on CO2 emissions and life cycle costs. The results of the sensitivity analysis show that the optimal variant of the green roof can be implemented in the cold and subtropical zone with regard to CO2 emissions, but not with regard to life cycle costs.

Optimizing Building Orientation for Passive Cooling

This research paper explores the application of passive design strategies in three museums in Lagos, Nigeria: The National Museum, Jaekel House, and the Heritage Museum in Badagry. The study focuses on building orientation as a key passive design strategy and evaluates its effectiveness in enhancing energy efficiency and thermal comfort in tropical climates. With the use of data collection from Google Earth Pro, a comparative analysis examines the architectural features and design elements of each museum, highlighting their use of building orientation, shading devices, and landscaping to optimize passive cooling and natural lighting. The innovative layout and strategic orientation of the National Museum demonstrate a successful integration of passive design strategies, while Jaekel House's use of deep overhangs and vegetation showcases a deliberate commitment to sustainable architecture. The Heritage Museum in Badagry, with its historical significance, presents an intriguing case study for passive design. While limited information is available, satellite imagery suggests an optimal orientation for passive solar design, complemented by deep overhangs and a reflective roof. The findings suggest that the three museums can benefit from further enhancements to their passive design strategies, including the integration of renewable energy sources, smart building systems, green roof systems, and water harvesting and management systems. In addition, educational initiatives can raise awareness and promote sustainable practices among visitors and the local community.

Impact of native vegetation and soil moisture dynamics on evapotranspiration in green roof systems

Evapotranspiration (ET) is an important water budget term for understanding the recovery of stormwater retention in green roof systems (GRs). However, ET evaluations, particularly in full-scale GRs, remain challenging. This study investigated ET dynamics within a GR in the City of Pittsburgh, USA, using a water balance based on continuously monitored soil moisture from moisture sensors over 15 months. Results suggest under well-watered soil conditions, daily moisture loss correlated with solar radiation, temperature, and humidity, in decreasing order of correlation strength, while wind speed had limited effects. Compared to sensor-informed moisture loss (using moisture-based water balance), the Hargreaves and FAO-56 Penman-Monteith equations predicted cumulative ET that was 1.8 and 2.1 times higher, respectively. When soil moisture declined and approached the temporary wilting points, a noticeable reduction in daily moisture loss was observed. This suggests the necessity of using a water stress coefficient alongside a crop coefficient to represent actual ET based on FAO-56 Penman–Monteith estimates. Seasonal crop coefficients from dominant native plant species present at our monitored location, eastern bluestar (Amsonia tabernaemontana) and creeping woodsorrel (Oxalis corniculata), had mean values of 0.48, 0.62, and 0.65 for fall, spring, and summer, respectively. The impact of water stress on ET could be characterized by a linear relationship with moisture content. Our results highlight the importance of soil moisture in regulating ET processes and demonstrate the utility of soil moisture data for evaluating ET in GRs and informing irrigation practices.

Green Roof Systems within the Framework of a Circular Economy: A Scoping Review

Green roofs are nature-based solutions with multiple benefits for the urban environment, but they have specific polymeric components in their structure that cause a carbon footprint. This scoping review highlights the technological advance in reusing or recycling alternative materials in green roof structures worldwide, making them a part of the circular economy (CE), and the search strategies to promote them to find whether there is a relation between them. The data were collected using the Web of Science from 2012 to 2022; we also used the Bibliometrix package to analyse research development by country and the development of the topic by author’s keywords. We selected 68 open-access articles from twenty-four countries and reviewed the grey literature from the top five productive countries on this topic. Our findings show that CE strategies are performed nationally, while the green roof promotion ones are concentrated at the city level. The theme co-occurrence analysis showed that the substrate is the primary layer used with alternative materials, and the three materials most applied for it are rubber, biochar, and hydrogel. It was found that the primary purpose of optimising green roofs with alternative materials is to increase the ecosystem services they provide and indirectly function within the circular economy; still, there is a gap in estimating the environmental impact of doing this as a potential CE activity.

Green Roof Systems for Rainwater and Sewage Treatment

Green roof systems are regarded as a viable solution for mitigating urban environmental challenges and offering a multitude of environmental benefits. Currently, green roofs are increasingly being utilized for the management of rainwater runoff and wastewater. The integration of decentralized rainwater and sewage on-site treatment technology with urban green buildings is being gradually promoted. Green roofs can also be considered as a form of decentralized rainwater and sewage on-site technology, which holds great potential for widespread adoption in the future. Several studies have suggested that green roofs may serve as a potential source of pollutants; however, there are also studies that clearly demonstrate the efficient removal of nutrients and organic pollutants by green roofs. This article critically examines the existing literature on water treatment aspects associated with green roofs and elucidates their classification and operational mechanisms. Through an analysis of previous research cases, it becomes evident that both substrate and vegetation play a significant role in influencing the treatment performance of green roofs. By designing and configuring appropriate substrate and vegetation, green roofs can play a pivotal role in the purification of water quality. Finally, a brief outlook is presented for the future research directions of green roofs, with the anticipation that green roofs will feature more innovative and environmentally friendly designs, as well as expanded prospects for application.

Acoustic absorption, scattering, and diffusion provided by green roof systems

Green roof systems can contribute to sustainable urban planning in terms of acoustics by absorbing sound energy and thereby reducing sound levels. However, these positive contributions may vary depending on the substrate's nature, the characteristics of the plants, and the extent of vegetation coverage.In this work, experimental measurements were carried out in both a reverberation chamber and in an anechoic chamber to assess the effect of two different substrates (an engineered substrate specifically prepared for green roof systems and an ordinary soil), three plant species (Thymus pulegioides, Festuca glauca, and Sedum sediforme), and three levels of vegetation coverage (0 %, 50 %, and 100 %) on the acoustic behaviour of a typical green roof system.Initially, the experimental setups and the characteristics of plants and substrates used are fully described. Subsequently, the results are analysed to inspect the individual and collective influence of the different variables on the sound absorption, scattering, and diffusion properties.The results confirmed the expected good sound absorption behaviour and the relatively lesser important scattering properties of the combined effect of substrate and plants. The substrate was found to have a significant impact on the acoustic absorption. Additionally, the scattering results suggest that plant morphology can also influence such systems’ acoustic behaviour.

Green roof thermal performance of small-scale prototype using IES-VE simulation in tropical climatic condition

Abstract This study investigates the thermal performance of green roof systems in a tropical climate, focusing on the small-scale building prototypes. Batu Pahat, Malaysia is experiencing the increasing temperatures due to climate change. Green roofs are considered as a potential solution, but their effectiveness depends on various factors such as building orientation, solar shading, and thermal resistance (R-value). Therefore, modeling and simulation are crucial for understanding green roof thermal behaviour. This study employs the Integrated Environmental Simulation Virtual Environment (IES-VE) software for analysis. Three identical small-scale buildings were constructed, one with Portulaca Grandiflora (PGR) plants, another with Alternanthera Paronychioides (ATN) plants, and a control roof with no vegetation. The R-values from the on-site green roofs were measured at 0.8899 m²K/W for PGR and 1.1477 m²K/W for ATN, while the control roof had an R-value of 0.1 m²K/W. Green roofs with higher R-values demonstrated a substantial reduction in indoor temperatures, making them a valuable solution for improving thermal comfort in tropical climates. This study underscores the importance of green roofs in mitigating rising temperatures in tropical climates. Simulation using IES-VE approved that green roofs can potentially reduce indoor temperatures, demonstrating their suitability for tropical regions. These findings have significant implications for sustainable building design and urban planning in hot and humid climates.

Facing Climate Change in a Temperate European City: Urban-Scale Diagnosis of Indoor Overheating and Adaptation Strategies for Residential Buildings

The rise in outdoor temperatures and heatwaves highlights the limitations of buildings in adapting to warming conditions, even in temperate climates. This paper analyses the indoor overheating of residential dwellings in Pamplona (a city in northern Spain, with a Cfb climate) using an urban-scale diagnostic methodology and presents different envelopes’ retrofitting scenarios as a strategy to reduce it. The results come from energy simulations conducted during an extremely warm summer in 2022, considering the microclimate effects. The residential typologies most vulnerable to overheating are those with only one orientation, built before the EPBD 2002, and located on top floors. These dwellings show a 23.7% mean of indoor overheating hours (IOH), representing approximately 870 h above the EN 16798-1:2019 adaptive threshold from May to September. Renovating building envelopes to meet current energy standards reduces the IOH by an average of 8.6% and up to 15.35% in the most vulnerable typologies. In the retrofitting scenario with green roof systems, indoor temperatures are up to 0.5 °C lower than when roofs are renovated with traditional systems. This study assists policy-makers in preventing the risk of overheating within cities and encourages them to promote nature-based solutions in order to adapt urban residential buildings and cities to warming conditions.

Analysing carbon impacts of green roof at Hilton Watford: life-cycle assessment approach

This paper investigates the environmental aspects and energy impacts of implementing a green roof system at the Hilton Watford hotel, utilising building information modelling software (Revit) for three-dimensional modelling and Insight for energy simulation. Following EN 15804:2012+A2:2019, the study employs life-cycle assessment methodology, focusing on embodied and operational carbon. Environmental Product Declarations, Inventory of Carbon and Energy database and the Royal Institution of Chartered Surveyors guideline inform embodied carbon calculations. The results show the green roof system releases 263 839.56 kgCO2e as embodied carbon, while its sedum layer sequesters 211 468.12 kgCO2e over a 50 year lifespan. Energy efficiency analysis indicates a 3.3 kWh/(m2/year) reduction in energy consumption, leading to a 112 130.31 kgCO2e reduction in operational carbon dioxide emissions, highlighting the environmental benefits of green roof adoption. The findings suggest a 0.35% mitigation of whole life-cycle carbon dioxide emissions, with greater impact in situations of lower insulation effectiveness, showcasing the potential of green roofs in reducing carbon dioxide emissions. Additionally, the green roof incurs a minimal financial burden, constituting only 0.51% of the overall project cost.

Operational effect of green roof systems with a modified substrate adding soda residue soil

ABSTRACT To investigate whether soda residue soil could be used as a green roof substrate, this paper setup six green roof systems with four materials (peat soil, coconut bran, perlite, and soda residue soil) mixed in different volume proportions. The effect of soda residue soil content on Sedum lineare growth and pollutant removal from the stormwater runoff was analyzed and the runoff quality index (RQI) was calculated. Results showed that the relative growth rate of S. lineare height in system B with 10% soda residue soil was about 21.5–53.2% higher than the other systems. The outflow of system B with 10% soda residue soil had the lowest mass concentration of NH4+-N and TN, which were 2.2 and 3.2 mg/L, respectively. The average repetitive rainfall retention rate of system A without soda residue soil was the lowest at 82.6%. System B had the highest RQI at about 0.71. It confirmed that soda residue soil can be a material with practical application value, and when the volume ratio of peat soil, coconut bran, perlite, and soda residue soil was 4:3:2:1, the green roof would have the best performance in regulating and purifying the initial rainwater runoff.

«Green» structures in the urbanized environment: studying the impact of «green» roofs on environmental parameters and rainwater quality. Bibliographic review

A quantitative analysis of the most cited articles published in the Scopus scientometric database by 2023 is carried out. It is shown that most of the publications, the object of study of which are "green" structures, focus on the study of "green" roofs. It is shown that since 1981, the number of studies on green roofs has been steadily increasing: approximately 45% of articles focus on the benefits in terms of thermal impact and thermal insulation, 18% on rainwater drainage, 15% on air quality, 5% on the noise-absorbing properties of green roofs, and 17% on the costs of building and operating green roofs, recreational facilities, fire protection, and other related issues. The requirements and commonly used materials for a standard green roof are described, as well as the percentage of scientific publications, depending on the functions and layers of green roof construction involved. An analysis of the most cited scientific studies on the impact of green roof systems on wastewater quality was conducted. It is shown that the results of the studies presented in these publications indicate the need for further study of the impact of a "green" roof on the amount of pollution in the water flowing from its surface. It is emphasized that further research should focus on the structural layers of the roof (thickness and materials used), namely the thickness and types of substrate layers, as well as on the conditions of plant care (e.g., fertilization), especially on intensive green roofs. In addition, it should be studied and analyzed how the retention of rainwater by plants and the soil layer of a green roof affects the relative humidity of the air near the building during periods without rain. The most cited scientific studies on the reduction of air pollutants by means of green roofs are analyzed. It is concluded that future research should focus on the study of plant species that are well adapted to growing on roofs (in temperate climates) and most effectively carry out the process of photosynthesis, absorbing CO2 and releasing O2 into the atmosphere around the building. The article analyzes the most cited scientific publications on the noise-absorbing properties of green roofs. It is substantiated that it is necessary to maximize the percentage of green roofs implementation on all buildings and structures in the city so that green roofs can significantly affect the quality of the environment in urbanized areas.

Evaluating the economic sustainability of commercial complex greening based on cost-benefit analysis: A case study of Singapore’s Shaw center

Commercial complex greening is the alternative to leading the greening development of public buildings, reducing the negative impact of buildings on the environment, and achieving sustainable development goals. However, the economic sustainability of commercial complex greening remains underinvestigated. This study investigated traditional building greening economic evaluation indicators and quantitative methods according to the characteristics of commercial complexes in to provide ideas on the economic evaluation of it to fill in the blanks of CBA analysis applied to the economics of greening systems of commercial buildings. Applying cost-benefit analysis, this study evaluated the economic sustainability of vertical greening systems (VGS) and green roof systems (GRS) installed on a commercial complex in Singapore using Net Present Value (NPV), Payback Period (PBP), and sensitivity analysis to quantify and integrate personal and social life cycle costs and benefits. The methodology was based on an extensive literature review in multiple fields and rational assumptions for unavailable data. The key findings were: 1) Commercial complex greening is a feasible investment. 2) VGS has a higher economic return value, whereas GRS can achieve faster payback. 3) Well-designed greening and vitality-boosting ideas bring more economic returns than tax incentives. 4) Property value improvement, maintenance cost, and fire risk reduction were sensitive factors affecting NPV, among which property value played a decisive role, especially for VGS. 5) Extensive construction and tax policies can reduce costs and improve the economy. 6) Personal benefits generated by greening are greater than social benefits. This critical case study of a commercial complex greening project provides greening developers and operators a better understanding of the economic competitiveness of commercial complex greening implementation to promote the market application and a rationale for governments to revise existing or formulate new measures to encourage the development of green industries. Although the conclusion of this study only focuses on the economic sustainability of greening in commercial complexes in Singapore due to sample size limitations, achieving a more significant localized evaluation is potential by collecting and replacing data corresponding to regions based on this research framework. Meanwhile, quantifying more economic indicators, comparing the economy of different greening modes in commercial complexes and arranging an international database about the economic sustainability of commercial complex greening are worth further exploration in the future.

A Critical Review of Existing Methods to Evaluate the Performance of Nature-Based Solutions (NBS) on Commercial Roofs (CR) to Mitigate Urban Flooding

The intensity and frequency of extreme rainfall events have increased in North America and the world due to climate change. Extreme rainfall events, characterized by a heavy volume of rainfall in a short duration, have triggered the onset of urban flash floods. Over the years, flash flooding has been reported in different cities in Canada, which resulted in many losses. Subsequently, different green roofing systems have been adopted to control urban stormwater runoff as part of Nature-Based Solutions (NBS) to mitigate urban flood and build a flood-resilient city. Currently, no specific widely recognized standard or code is dedicated to determining the hydrological performance of green roofs as a whole system. Moreover, there are no test protocols to regulate the design of green roof systems in the market. A comprehensive literature review examines existing research methods adopted to evaluate influencing parameters affecting the hydrological performance of NBS-CR. The results indicate several limitations in experimental and field investigations. Consequently, to address these limitations, it is essential to formulate a multi-functional work plan to develop a standardized test method that can become a common platform for the roofing industry to test and quantify the hydrological performance of their systems.

Earlier Flowering Phenology and Pollinator Visitation on Urban Green Roofs Compared to Ground-Level Gardens

Urban green space, green infrastructure, and horticultural installations are gaining recognition for their potential to foster biodiversity. Green roofs are challenging growing environments for plants, characterized by extreme substrate temperatures, high light intensity, limited moisture availability, and limited substrate depth. Plants have a variety of physiological responses to these unique conditions, but little is known about how green roof growing conditions affect ecological characteristics like plant flowering phenology. Meanwhile, studies are only just uncovering the degree to which green roofs can provide habitat and support urban pollinator biodiversity. We evaluated the flowering phenology and made in situ pollinator observations of 15 plant taxa growing both on green roof systems and at ground level in Denver, Colorado, over two growing seasons. We found that flowering phenology occurs substantially earlier on green roofs compared to ground level among the observed plant taxa and observed a greater number of pollinators on green roofs early in the season, compared to ground level, presumably due to the availability of floral resources among the observed plant taxa. We observed significantly higher substrate temperatures along with wider diurnal temperature amplitude during the growing season that may contribute to the observed phenological patterns. Divergence in flowering phenology between individual plants of the same species on green roofs and plants at ground-level may have implications for organisms that rely on floral resources in urban environments. Earlier flower initiation on green roofs may provide pollinators with unique foraging opportunities and aid targeted conservation where early-season floral resources are limited.

Tolerance of Tall Fescue (Festuca arundinacea Schreb.) Growing in Extensive Green Roof Systems to Saline Water Irrigation with Varying Leaching Fractions

As urbanization intensifies environmental challenges in contemporary cities, widespread green roof installations emerge as a potential solution. This study explores irrigating tall fescue (Festuca arundinacea Schreb.) turfgrass with saline water in extensive green roof systems, aiming to conserve freshwater resources. The objectives include determining the period of saline water tolerance and identifying the leachate electrical conductivity threshold affecting tall fescue’s green coverage. This greenhouse study comprised 24 lysimeters equipped with extensive green roof layering. Treatments included three NaCl irrigation solutions with an electrical conductivity of 3 dS m−1, 6 dS m−1, and 9 dS m−1, while tap water served as the control. Additionally, irrigation treatments were applied at two different regimes, resulting in an average leaching fraction of 0.3 for the low irrigation regime and 0.5 for the high irrigation regime. Tall fescue’s tolerance to saline water was evaluated through the determination of green turf cover (GTC) as well as the clipping dry weight and the leachate electrical conductivity (ECL) draining from the lysimeters. It was found that tall fescue turfgrass growing in extensive green roof systems can tolerate irrigation with water of electrical conductivity up to 9 dS m−1 for extended periods, approximating three months, without GTC declining below 90%, provided that a minimum leaching of 30% is maintained. Furthermore, irrigating with water at 9 dS m−1 resulted in a 24.5% reduction in cumulative clipping dry weight over the four-month study period. The regression analysis between GTC and ECL highlighted a substantial decline in GTC when ECL surpassed the critical threshold of 12.5 dS m−1.

Multicriteria decision-making tool for investigating the feasibility of the green roof systems in Egypt

Urbanization in Egypt detracts from green spaces, reduces the per capita green ratio, and increases adverse effects such as heat islands, air pollution, and energy consumption. In addition, it affects social human comfort issues. In this context, building rooftops is a potential solution that could reduce the impact of green space scarcity. Such a solution has multiple evidence-based environmental, economic, and social benefits. Consequently, numerous governmental and private initiatives have spread the rooftop greening concept in Egypt. These initiatives have adopted several planting systems, such as soil-based, deep-water culture, and nutrient film technique systems. This manuscript examines these prevalent systems through environmental, economic and social lenses. This paper pioneers a user-centric tool to facilitate the system selection that aligns with individual needs. An analysis was conducted to ascertain the value of various factors influencing system choice, encompassing a literature review, expert opinion solicitation, market survey, and energy simulation. The Analytical Hierarchy Processes methodology was proposed to appraise the factors, aiding in arriving at an informed decision. The paper presents a novel contribution by studying many factors spanning diverse scientific domains. Furthermore, creating an accessible decision-support tool encapsulates a substantial addition to the body of knowledge.

A Rooftop Agrivoltaic System: Pollinator Plant Establishment

In a time of rapid habitat removal in favor of urbanization, green roofs have been recognized as a means to increase biodiversity while emulating native habitats in urban ecosystems. There is often competition over roof space for use as solar energy generation, or green roof space. Here we explore the inclusion of both green roof and photovoltaic (PV) energy generation systems stacked vertically in a rooftop system to better understand the impacts of PV arrays on six species of pollinator plants native to Colorado’s Front Range and Great Plains Regions. We conducted randomized and replicated plant establishment and growth studies in a simulated rooftop system in full sun and under a fixed mounted PV array over the course of the initial growing season. Additionally, we measured the plant growing environment, including air temperature, substrate temperature, and substrate moisture to quantify the differences in the conditions in full sun compared to conditions under the PV arrays. Light conditions were modeled. We find plant establishment and overwinter survivability is greater under the PV array, while the seasonal plant growth index varies depending on the plant species. Substrate moisture was significantly higher under the PV while substrate temperature trended towards lower daytime temperatures and slightly raised nighttime temperatures under the PV. Based on this study, the microclimate under the PV array is amenable to plant growth, and differences in plant response to the shade may closely resemble ecotones found in nature. The combination of rooftop agrivoltaics and traditional full sun green roof plantings may lead to greater native plant establishment, and therefore greater diversity of habitat niches in the built environment.