Query: Roof gardening plants water ababsorption capacity

title: Green roof storage capacity can be more important than evapotranspiration for retention performance.
abstract: Green roofs can significantly reduce stormwater runoff volumes. Plant selection is crucial to retention performance, as it is influenced by how well plants dry out substrates between rainfall events. While the role of plants in evapotranspiration (ET) on green roofs is well studied, their potential influence on retention via their impacts on water movement through substrates is poorly understood. We used a simulated rainfall experiment with plant species with different water use strategies to determine the key drivers of green roof retention performance. Overall per event retention was very high (89 95% and similar for all plant species and unplanted modules for small events. However, for larger events, some species showed lower retention than unplanted modules or low water using succulent species. Despite the fact that these species were more effective at replenishing storage between rainfall events due to their higher ET, they reduced the maximum storage capacity of the substrate, likely due to their root systems creating preferential flow paths. This finding has important implications for green roofs, as although ET represents the primary means by which the storage capacity of green roofs can be regenerated, if species with high ET also reduce the maximum storage capacity, effective retention performance is reduced. Therefore, we suggest that species selection must first focus on how plants affect storage capacity in the first instance and consider water use strategies as a secondary objective.

title: Influence of the Hydrogel Amendment on the Water Retention Capacity of Extensive Green Roof Models
abstract: The goal of the research was to investigate the retention capacity of six green roof models (SHP1, SHP2, SHP3, SH, S, and SP) constructed with the use of the square shaped plastic trays, Floradrain FD 25 drainage elements, SF filter sheets, and the specified extensive substrates (with or without the hydrogel amendment) The SHP1 and SHP2 models were constructed in March 2017, SHP3 and SH in November 2017, while S and SP in April 2018. Four models (SHP1, SHP2, SHP3, and SP) contained the plants (the goldmoss stonecrop Sedum Acre) whereas two models (S and SH) did not contain the vegetation. The substrates of SHP1, SHP2, SHP3, and SH models contained the hydrogel admixtures. The investigations were conducted with the use of simulated (and partially natural) precipitations. The water retention capacity of each green roof model was established based on the difference between the precipitation volume and the volume of runoff from a model. The results show that green roofs can be useful stormwater management tools. The calculated stormwater retention rates ranged from 29.50% to 85.15% In most cases, the best water retention capacity was exhibited by the SHP3 model, constructed in November 2017 and planted in April 2018, containing the substrate amended with superabsorbent (cross linked potassium polyacrylate) The similarly constructed SHP1 and SHP2 models, which were built in March 2017, in some cases had lower water retention capacity. These models contained older hydrogel and were overgrown with older, smaller, and worse looking plants, partially supplanted by mosses. Such results indicate that the efficiency of hydrogel may decrease over time. In many cases, the S (not vegetated, without hydrogel) SH (not vegetated, with substrate containing hydrogel) and SP (vegetated, without hydrogel) models had slightly lower water retention capacity. The results of investigations indicate that there was a relatively strong positive linear correlation between the retention depth and duration of the antecedent period elapsed from the preceding total (or substantial) saturation of the green roof models (labelled in this article as period since total saturation PSTS) The weather conditions i.e. air temperature and relative humidity as well as PSTS are very important parameters that influence the retention capacity of the green roof models. The result show that duration of PSTS can be stronger correlated with the retention depth than antecedent dry period (ADP) elapsed from the end of last precipitation, regardless of its depth and intensity.

title: Heat transfer in a lightweight extensive green roof under water freezing conditions
abstract: This paper presents a study of the thermal response of lightweight extensive green roofs with lightweight mineral wool growing media in wintertime in water freezing conditions. A model of green roof heat and mass transfer was developed, which considers sensible as well as latent heat accumulation in plants and lightweight mineral wool growing media using an apparent heat capacity method. The model was validated with in situ experiments. The influence of latent heat storage on the thermal response of a green roof was studied for different climatic conditions. The results of numerical analyses showed that the process of water freezing further improves the energy efficiency of green roofs, because the peak heat flux at the inner surface of the roof is up to 30% lower in comparison to the non vegetated roof. It is shown that latent heat storage significantly contributes to decreasing heat losses during wintertime, which are approximately 5% to 20% lower in comparison to non vegetated roofs.

title: "Greenhousing" Integrating Low Input Simplified Hydroponics for Roof Gardening in Bologna's Public Housing
abstract: Since 2007, most people of the world live in cities. Urban agriculture, and more specifically urban horticulture may allow improvements in food supply and reduce the city ecological footprint. Furthermore, gardening practices are associated with social and therapeutic effects. In the last decades, as a consequence of the increased awareness on its related benefits, urban horticulture has assumed a paramount role in defining the city landscape. It is true, however, that within cities, the main constraint to the expansion of agriculture is represented by land availability and soil fertility. Simplified soilless gardens are getting more popular worldwide since they allow cultivation in courtyards, small gardens, walls, balconies, and rooftops, also by intensifying production per surface area, since plants are provided with nutrient and water according to their needs. Moreover, simplified soilless systems may use low cost recycled materials to build growing containers, and through the adoption of closed cycles water and nutrients efficiency is improved. Starting from 2011, the Greenhousing project aims at the introduction of soilless gardens in the rooftop of public housing buildings of the city of Bologna, Italy. In the present paper the beneficial elements of multifunctionality of these gardens will be outlined.

title: Water Resilience by Centipedegrass Green Roof: A Case Study
abstract: Centipedegrass (Eremochloa ophiuroides) is a low maintenance turfgrass. The first extensive green roof of centipedegrass was established in TongZhou Civil Squares in 2014. However, storm water runoff reduction, water retention capacity, and plant water requirements by a centipedegrass green roof has not yet been defined. The soil moisture dynamics, rainwater retention capacity, runoff reduction, and plant evapotranspiration were investigated by simulated centipedegrass green roof plots, which were constructed in the same manner as the green roofs in TongZhou Civil Squares in 2018. The results showed that the centipedegrass green roof retained 705.54 mm of rainwater, which consisted 47.4% of runoff reduction. The saturated soil moisture was 33.4 0.6% the excess rainfall over the saturated soil moisture resulted in runoff. The capacity of rainwater retention was negatively related to the soil moisture before rain events and was driven by plant evapotranspiration. Drought symptoms only occurred three times over the course of a year when the soil moisture dropped down to 10.97% Our results indicate that the rainwater retained in the soil almost met the needs of plant consumption; a further increase of rainwater retention capacity might achieve an irrigation free design in a centipedegrass green roof.

title: Water retention performance of green roof technology: A comparison of canadian climates
abstract: In recent decades, urbanization has led to more frequent flood events in urban areas. Several studies have shown the promise of green roof technology for storm water reduction. However, limited studies have assessed water retention performance of green roofs in a range of climates. To investigate the retention performance of a green roof in various Canadian climates, several cities across the country (Vancouver, Calgary, Regina, Toronto, London, and Halifax) were selected. The water balance equation along with evapotranspiration (ET) models were employed to simulate runoff produced by green roofs in these six Canadian cities for two different vegetation types. A seven year simulation period was selected running from 2000 to 2006, with modeling conducted for eight months of the year using hourly time steps. The results showed that the performance of a green roof in runoff reduction depends on location, varying from 17% to 50% for low water use plants. The best performance in storm water reduction was predicted to occur in Regina and Calgary, while the poorest performance was predicted for Halifax and Vancouver. However, the average annual water retention (mm) was the highest in Toronto and London and the lowest in Vancouver, with Calgary, Regina and Halifax showing intermediate performance. Sensitivity analyses were performed for substrate depth, porosity, and wilting point to determine the importance of each for green roof performance for the different cities. The results revealed that the vegetation type had a greater impact on the water retention performance of green roofs than increases in substrate storage capacity associated with different substrate depth, porosity and wilting point over the range assumed in this study.

title: Thermal regulation capacity of a green roof system in the mediterranean region: The effects of vegetation and irrigation level
abstract: The increasing interest in green roof implementation and research is based on the environmental benefits of this technique. The thermal regulation capacity of a green roof system is considered a very relevant benefit due to its environmental and economic interest. In this study, an experimental modular evaluation was performed to quantify the contribution of vegetation cover by evaluating two Mediterranean native species and the effect of irrigation water volume on the thermal capacity of a green roof system in a Mediterranean area. A positive effect of the vegetation presence was evidenced, with important substrate temperature reductions during spring and summer. Daily heat gain and loss were reduced as a consequence of vegetation presence. Sedum sediforme performed as a better insulator than Brachypodium phoenicoides during the experimental period in spring and summer, with few differences in autumn and winter. The modules with the 25% of potential evapotranspiration applied as limited irrigation reported lower heat flux values than well irrigated module (considered as 50% of potential evapotranspiration) in all seasons. The plant response to irrigation treatment is here evaluated to explain the thermal regulation effect during the whole year. The main conclusion is that there is a positive influence of species selection and irrigation management in the thermal regulation properties of green roofs under Mediterranean conditions.

title: Biochar makes green roof substrates lighter and improves water supply to plants
abstract: a b s t r a c t Green roofs are increasingly being built to manage stormwater runoff in cities. Water retention addi tives such as biochar could be a useful way of increasing substrate water holding capacity (WHC) and therefore stormwater retention without increasing substrate weight loading. If this also increases plant available water (PAW) plant selection could be expanded to species with higher water use, further reduc ing stormwater runoff by drying substrates after rain. We examined the effects of adding one type of green waste biochar (0, 10, 20, 30 and 40% v/v) to two scoria based substrates (with or without added organic matter) on WHC, bulk density, PAW and days taken to reach permanent wilting point (PWP) Biochar significantly improved WHC, increasing with greater additions of biochar. Increased water was also plant available, with 30% biochar increasing PAW by 16% (scoria with organic matter) and PWP by 2 days in both substrates. Biochar did not affect plant growth or biomass allocation. Application of 30% biochar was optimal for PAW and delaying PWP. However, as 40% biochar significantly increased WHC, this rate will likely be optimal for stormwater retention, with an additional 2.3 cm rainfall/cm area retained in 10 cm deep substrates. Biochar also significantly reduced bulk density, substrates with 40% biochar could have an additional 1.5 cm/m 2 of depth compared to the same weight as scoria only, further increasing PAW and rainfall retention. Consequently, in this study, biochar addition makes green roof substrates lighter and improves plant water supply; potentially expanding plant selection in dry climates and improving their stormwater retention.

title: Laboratory Tests of Substrate Physical Properties May Not Represent the Retention Capacity of Green Roof Substrates In Situ
abstract: Green roofs can be used to reduce the volume of polluted stormwater that is generated by cities. Modelling rainfall retention is critical, but green roof water balance models often rely on the physical properties of substrates. In these models, substrate water holding capacity (WHC) determines the depth of water which can be stored before runoff is generated; whereas, the permanent wilting point (PWP) limits evapotranspiration. The WHC and PWP, as well as plant available water (PAW; where PAW WHC PWP) as determined from laboratory tests, may not truly reflect how substrates perform on green roofs. We therefore ran a simulated rainfall experiment on green roof modules to (i) compare the rainfall retention of vegetated and non vegetated substrates with different WHC and PAW, and (ii) relate retention to substrate storage capacity, as calculated from laboratory measures of WHC and PAW. We found that the PAW of a substrate is a better indicator of evapotranspiration and retention when compared with WHC. However, we also found that substrates always retained less water than their calculated storage capacity would suggest, most likely being due to their high permeability. Our results indicate that using laboratory derived measures of WHC and PAW in green roof models may be over estimating both evapotranspiration and rainfall retention.

title: A framework for optimizing hydrologic performance of green roof media.
abstract: One of the primary functions of green roofs in urban areas is to moderate rainwater runoff, and one of the major impediments to the survival of plants on an extensive green roof (EGR) is a lack of available water during dry periods. Runoff moderation and water storage are both influenced by the composition of the growing media. Here we present a framework for evaluating the hydrologic performance of EGR growing media and also provide hydrologic attribute data for several commonly used EGR media constituents. In this three phase study, we: 1) measured hydrologic attributes of individual EGR media constituents, 2) predicted attributes of media mixtures using individual constituent data, and 3) tested the seven top ranking mixtures to evaluate hydrologic performance. Hydrologic attributes included wet weight and water held at maximum retentive capacity, long term water retention, and hydraulic conductivity. Because perlite was light in weight yet held the greatest amount of water both at its maximum retentive capacity and in the long term, media mixtures dominated by perlite were predicted to have the best overall hydrologic performance. Mixtures dominated by pumice were also predicted to perform relatively well but were heavier. Despite the slightly greater weight and slightly lower performance, pumice may be a preferred alternative to perlite because perlite is a processed constituent with greater estimated embodied energy. Results indicate that performance of mixtures can be adequately predicted using performance of individual constituents for wet weight, water held, and long term water retention. Hydraulic conductivity was less predictable because the pore volume in mixtures can be unrelated to the pore volume of the individual constituents. The framework presented here can be used to evaluate the performance of other EGR media, and the media attribute data can be used in formulating EGR media mixtures for specific applications. In addition, the attribute data can serve as a benchmark for evaluating other EGR media. Our results underscore the need for standardization of methods for more effective comparisons of EGR substrates, and also reinforce the need to evaluate EGR components using real world scenarios.