Developing resilient green roofs in a dry climate

Nationwide Evaluation of Urban Energy System Resilience in China Using a Comprehensive Index Method

The carbon peak and carbon neutrality goals for China signify a critical time of energy transition in which energy resilience is a vital issue. Therefore, a comprehensive evaluation of urban energy system resilience (UESR) is important for establishing a theoretical foundation. To this end, in this paper, 309 Chinese cities were evaluated using a comprehensive UESR assessment framework composed of 113 indices that measured vulnerability and capabilities of resistance and restoration. The results showed that China’s UESR is distributed unevenly and that cities in the eastern region generally have higher resilience than those in other regions. The minimum and maximum UESR results corresponded to Tibet and Shandong, respectively, at the provincial level and Rikaze and Weifang, respectively, at the city level. Regression analysis showed a positive correlation among UESR, carbon dioxide emissions, and GDP.

The Hindrances to Green Roof Adoption in a Semi-Arid Climate Condition

Green roofs (GRs) offer several environmental, social, and economic benefits while numerous barriers are limiting their adoption. This study covers two gaps in the literature: first, the lack of indicating separate hindrances to different types of GRs; second, the dearth of research related to the hindrances on GR adoption in any climate of Iran. This research aims to identify and analyze the importance of hindrances to GR adoption by considering the two major types of GRs using the Fuzzy Delphi Method (FDM) and Fuzzy Analytic Network Process (FANP), respectively. The results indicated that eight out of twenty-five identified hindrances to GR adoption were rejected using FDM. Moreover, it was found that although financial hindrances are significant for both types of GRs, public awareness is the most important hindrance to extensive GR adoption. As the first research of its kind in a semi-arid climate of Iran, the findings of this research provide an insight for the researchers and policymakers regarding the hindrances to GR adoption for further research and action.

Stormwater Retention and Reuse at the Residential Plot Level—Green Roof Experiment and Water Balance Computations for Long-Term Use in Cyprus

Green roofs can provide various benefits to urban areas, including stormwater retention. However, semi-arid regions are a challenging environment for green roofs as long dry weather periods are met with short but intense rainfall events. This requires green roofs to retain maximum volumes of stormwater, while being tolerant to minimal irrigation supplies. The objectives of this study are (i) to quantify the stormwater retention of two substrate mixtures with two plant species under natural rainfall; (ii) to assess the performance of two plant species under two levels of deficit irrigation; and (iii) to compute stormwater runoff reduction and reuse by green roofs and rooftop water harvesting systems for three standard residential plot types in urban Nicosia, Cyprus. A rooftop experiment was carried out between February 2016 and April 2017 and results were used to compute long-term performance. Average stormwater retention of the 16 test beds was 77% of the 371-mm rainfall. A survival rate of 88% was recorded for Euphorbia veneris and 20% for Frankenia laevis, for a 30% evapotranspiration irrigation treatment. A combination of a green roof, rainwater harvesting system and 20-m3 tank for irrigation and indoor greywater use reduced stormwater runoff by 47–53%, for the 30-year water balance computations.

Life cycle analysis of a new modular greening system

The construction and use of buildings represent about half of the extracted materials and energy consumption, and around one third of the water consumption and waste produced in the European Union. Therefore it is becoming more important to use sustainable materials that reduce the environmental impacts of construction, by conserving and using resources more efficiently. Green walls can be used as a sustainable strategy to reduce the environmental impact of buildings. The aim of this study is to evaluate the environmental impact of a new modular system for green roofs and green walls (Geogreen) which uses waste and sustainable materials in its composition. A life cycle analysis (LCA) is used to evaluate the long term environmental benefits of this system. The life cycle analysis (LCA) is carried according to ISO 14040/44 using GaBi software and CML 2001 impact category indicators. The adopted functional unit is the square meter of each material required to assemble the Geogreen system. This study also compares the environmental performance of the Geogreen system with other living wall systems and other cladding materials using data from the literature. This LCA study of the Geogreen system became relevant to identify a curing process with a major impact on GWP due to the energy consumed in this process. A change on this process allowed reducing 74% of the overall GWP. After this change it can be noticed that the Geogreen System presents one of the lowest environmental burden when compared to other construction systems.

Water quality function of an extensive vegetated roof

In this paper we present the results of a four-year study of water quality in runoff from an extensive, sedum covered, vegetated roof on an urban commercial building. Monitoring commenced seven months after the roof was constructed, with the first growing season. Stormwater drainage quality function of the vegetated roof was compared to a conventional (impermeable, high-albedo) membrane roof in addition to paired measurements of wet and bulk depositions at the study site. We present concentrations and fluxes of nutrients and major solutes. We discuss seasonal and year-to-year variation in water quality of drainage from the vegetated roof and how it compares with atmospheric deposition and drainage from the impermeable roof. Drainage waters from the vegetated roof exhibited a high concentration of nutrients compared to atmospheric deposition, particularly during the warm temperature growing season. However, nutrient losses were generally low because of the strong retention of water by the vegetated roof. There was marked variation in the retention of nutrients by season due to variations in concentrations in drainage from the vegetated roof. The vegetated roof was a sink of nitrogen, total phosphorus and chloride, and a source of phosphate and dissolved inorganic and organic carbon. Chloride exhibited elevated inputs and leaching during the winter. The drainage from the vegetated and impermeable roofs met the United States Environmental Protection Agency freshwater standards for all parameters, except for total phosphorus.

Optimal selection and placement of green infrastructure to reduce impacts of land use change and climate change on hydrology and water quality: An application to the Trail Creek Watershed, Indiana

The adverse impacts of urbanization and climate change on hydrology and water quality can be mitigated by applying green infrastructure practices. In this study, the impacts of land use change and climate change on hydrology and water quality in the 153.2 km(2) Trail Creek watershed located in northwest Indiana were estimated using the Long-Term Hydrologic Impact Assessment-Low Impact Development 2.1 (L-THIA-LID 2.1) model for the following environmental concerns: runoff volume, Total Suspended Solids (TSS), Total Phosphorous (TP), Total Kjeldahl Nitrogen (TKN), and Nitrate+Nitrite (NOx). Using a recent 2001 land use map and 2050 land use forecasts, we found that land use change resulted in increased runoff volume and pollutant loads (8.0% to 17.9% increase). Climate change reduced runoff and nonpoint source pollutant loads (5.6% to 10.2% reduction). The 2050 forecasted land use with current rainfall resulted in the largest runoff volume and pollutant loads. The optimal selection and placement of green infrastructure practices using L-THIA-LID 2.1 model were conducted. Costs of applying green infrastructure were estimated using the L-THIA-LID 2.1 model considering construction, maintenance, and opportunity costs. To attain the same runoff volume and pollutant loads as in 2001 land uses for 2050 land uses, the runoff volume, TSS, TP, TKN, and NOx for 2050 needed to be reduced by 10.8%, 14.4%, 13.1%, 15.2%, and 9.0%, respectively. The corresponding annual costs of implementing green infrastructure to achieve the goals were $2.1, $0.8, $1.6, $1.9, and $0.8 million, respectively. Annual costs of reducing 2050 runoff volume/pollutant loads were estimated, and results show green infrastructure annual cost greatly increased for larger reductions in runoff volume and pollutant loads. During optimization, the most cost-efficient green infrastructure practices were selected and implementation levels increased for greater reductions of runoff and nonpoint source pollutants.

Increases in the climate change adaption effectiveness and availability of vegetation across a coastal to desert climate gradient in metropolitan Los Angeles, CA, USA

Urbanization has increased heat in the urban environment, with many consequences for human health and well-being. Managing climate change in part through increasing vegetation is desired by many cities to mitigate current and future heat related issues. However, little information is available on what influences the current effectiveness and availability of vegetation for local cooling. In this study, we identified the variation in the interacting relationships among vegetation (normalized difference vegetation index), socioeconomic status (neighborhood income), elevation and land surface temperature (LST) to identify how vegetation based surface cooling services change throughout the pronounced coastal to desert climate gradient of the Los Angeles, CA metropolitan region, a megacity of >18 million residents. A key challenge for understanding variation in vegetation as a climate change adaptation tool spanning neighborhood to megacity scales is developing new "big data" analytical tools. We used structural equation modeling (SEM) to quantify the interacting relationships among socio-economic status data obtained from government census data, elevation and new LST and vegetation data obtained from an airborne imaging campaign conducted in 2013 for the urban and suburban areas across a series of fifteen climate zones. Vegetation systematically increased in cooling effectiveness from 6.06 to 31.77 degrees with increasing distance from the coast. Vegetation and neighborhood income were positively correlated throughout all climate zones with a peak in the relationship occurring near 25km from the coast. Because of the interaction between these two relationships, we also found that higher income neighborhoods were cooler and that this effect peaked at about 30km from the coast. These results show the availability and effectiveness of vegetation on the local climate varies tremendously throughout the Los Angeles, CA metropolitan area. Further, using the more inland climate zones as future analogs for more coastal zones, suggests that in the warmer climate conditions projected for the region the effectiveness of vegetation for regional cooling may increase thus acting as a localized negative feedback mechanism.

Water quality and quantity investigation of green roofs in a dry climate

Low-energy pollutant removal strategies are now being sought for water sensitive urban design. This paper describes investigations into the water quality and quantity of sixteen, low-maintenance and unfertilized intensive and extensive green roof beds. The factors of Slope (1° and 25°), Depth (100 mm and 300 mm), Growing media (type A, type B and type C) and Species (P1, P2 and P3) were randomized according to a split-split plot design. This consisted of twelve vegetated green roof beds and four non-vegetated beds as controls. Stormwater runoff was collected from drainage points that were installed in each area. Samples of run-off were collected for five rainfall events and analysed for water retention capacity and the water quality parameters of NO₂, NO₃, NH₄, PO₄, pH, EC, TDS, Turbidity, Na, Ca, Mg and K. The results indicated significant differences in terms of stormwater water quality and quantity between the outflows of vegetated and non-vegetated systems. The water retention was between 51% and 96% and this range was attributed to the green roof configurations in the experiment. Comparing the quality of rainfall as inflow, and the quality of runoff from the systems showed that green roofs generally acted as a source of pollutants in this study. In the vegetated beds, the intensive green roofs performed better than the extensive beds with regard to outflow quality while in the non-vegetated beds, the extensive beds performed better than intensive systems. This highlights the importance of vegetation in improving water retention capacity as well as the role of vegetation in enhancing pollutant removal in green roof systems. In addition growing media with less organic matter had better water quality performance. Comparison of these results with national and international standards for water reuse confirmed that the green roof outflow was suitable for non-potable uses such as landscape irrigation and toilet flushing.