Hydrological Performance of Green Roofs in Mediterranean Climates: A Review and Evaluation of Patterns

The capacity of green roofs to intercept rainfall, and consequently store and slow runoff resulting in a reduction in flood risk, is one of their main advantages. In this review, previous research related to the influence of green roofs on the hydrological cycle is examined with a special focus on studies for Mediterranean climate conditions (Csa and Csb according to the Köppen–Geiger climate classification). This climate is characterized by short and intense rainfall occurrences which, along with the increased area of impervious surface on Mediterranean regions, intensify the risk of flooding, particularly in the cities. The analysis covers the variables rainfall retention (R, %), runoff delay (RD, min or h), peak delay (PD, min or h), peak attenuation (PA, %), and runoff coefficient (RC, −), in relation to physical features of the green roof such as layers, substrate depth, slope, and vegetation, as well as, weather conditions, such as monthly temperature and monthly precipitation. Following a statistical analysis, some patterns for the average rainfall retention (%) were found in the published literature for green roofs under Mediterranean climate conditions—namely, that the most significant variables are related to the substrate depth, the existence of certain layers (root barrier, drainage layer), the origin of the vegetation, the types of green roofs (extensive, semi-intensive, intensive), and the precipitation and temperature of the location. Moreover, a multivariate analysis was conducted using multiple linear regression to identify the set of green roof features and weather conditions that best explain the rainfall retention (%), taking into consideration not only the studies under Mediterranean conditions but all climates, and a similar pattern emerged. Recommendations for future research include addressing the effect of physical features and weather conditions on the other variables (RD, PD, PA, RC) since, although present in some studies, they still do not provide enough information to reach clear conclusions.

РОЛЬ ЕКОЛОГІЧНИХ ФАКТОРІВ У ФОРМУВАННІ ПСЕВДОМЕЙОБЕНТОСУ (TEMPORARY MEIOFAUNA) ОДЕСЬКОГО РЕГІОНУ ЧОРНОГО МОРЯ

An analysis of long-term studies has made it possible to characterize the formation density of pseudomeiobenthos (temporary meiofauna) settlements depending on the substrate, depth, and seasons of the year in the Odessa Sea region of the northwestern Black Sea by the example of oligochaetes, polychaetes and juvenile mollusks. Their largest accumulations (the total density of settlements was 30865.8±5384.3 ind m-2) are characteristic of the ground sand/shell, the smallest for silty substrate (averaged 11705.5±1337.8 ind.m-2). The maximum indices of the total number of temporary meiofauna were recorded on depth of 10-15 m (20826.3±5010.4 ind.m-2). As shown by long-term studies, the average indicators of the total number of meiobenthos are highest in the winter period. The same applies to the density of the temporary component.

The influence of habitat preference on longitudinal population composition and distribution of Groupers (Serranidae) in Chumbe Island Coral Park, Zanzibar, Tanzania

A survey of six common grouper (Serranidae) species was conducted on both the western protected and eastern unprotected reefs around Chumbe Island, Zanzibar. Species, estimated maturity, and habitat were recorded using standardized categories. Fundamental niche and general habitat preference were extrapolated based on observed realized niche and qualified based on substrate, depth, slope position, and general reef region. Taking habitat preference into account, abundance and biomass density of serranid populations were compared between locations on the reef in order to best account for how habitat influences distribution and population health. The results of this study provide depth to previous research on the protected reef and indicate noteworthy shifts in population composition between 2014 and 2018 that favour species with less specified habitat preference, such as Aethaloperca rogaa and Cephalopholis argus. Surveys of Chumbe’s nearby unprotected eastern reef indicate low levels of species abundance, which this study hypothesizes is the result of inappropriate habitat structure, increased fishing pressure, and decreased population health within the MPA. Ultimately, this study suggests that MPAs do not protect all species equally, and habitat preference must be taken into account when assessing MPA effectiveness at protecting different species. Indeed, especially as serranid habitat faces continued degradation, serranid conservation will depend even more on protection of each species’ preferred habitat in coral systems. As such, assessing serranid populations as a whole fails to capture the changes in population distribution and composition that is occurring between species, which may be more indicative of shifts and disturbances in the ecosystem.

Vegetation cover and plant diversity on cold climate green roofs

Both vegetation abundance and community composition play important roles in functions of green roofs (e.g. stormwater retention, habitat provision, aesthetic appearance). However, green roofs’ vegetation, and hence their functions, can change significantly over time. More understanding of these changes is required, particularly in cold climates. Therefore, this study investigated vascular plant covers and species compositions on 41 roof sections located in Sweden’s subarctic and continental climate zones. For the roof sections with a known originally intended vascular plant composition (n = 32), on average 24 ± 9% of the intended species were detected in surveys, and unintended species accounted for 69 ± 3% of the species found. However, most colonizing species formed sparse cover on the roofs. Thus, they may make less contributions to green roofs’ potential functionalities related to vegetation density (e.g. social perception, effectiveness in stormwater management and thermal performance) than the intended vegetation. The intended species dominated plant cover (93 ± 3%) and Sedum acre (58 ± 36% cover) was the most commonly detected species and as found in previous studies, substrate depth was positively related to both plant cover and species richness. Contrary to a hypothesis, the roofs’ vascular plant cover was not related to species richness but was significantly and negatively correlated with moss cover. The results highlight the importance of substrate depth for both plant abundance and species diversity and show that even in a cold climate, colonizing unintended species can strongly contribute to green roofs’ species richness.

Probabilistic assessment of hydrologic retention performance of green roof considering aleatory and epistemic uncertainties

Green roofs (GRs) are well known for source control of runoff quantity in sustainable urban stormwater management. By considering the inherent randomness of rainfall characteristics, this study derives the probability distribution of rainfall retention ratio and its statistical moments. The distribution function of can be used to establish a unique relationship between target retention ratio , achievable reliability AR, and substrate depth h for the aleatory-based probabilistic (AP) GR design. However, uncertainties of epistemic nature also exist in the AP GR model that makes AR uncertain. In the paper, the treatment of epistemic uncertainty in the AP GR model is presented and implemented for the uncertainty quantification of AR. It is shown that design without considering epistemic uncertainties by the AP GR model yields about 50% confidence of meeting . A procedure is presented to determine the design substrate depth having the stipulated confidence to satisfy and target achievable reliability .

Legislative requirements related to substrate depth as a barrier to the construction of green roofs in Bulgaria

There are 265 municipalities in Bulgaria. According to the national legislation, each Municipal Coun-cil adopts an Ordinance for the construction and protection of the green system. Most of the mu-nicipalities have such ordinances, however, only 75 of them stipulate regulative requirements, under which a green roof can be considered a green area. These requirements refer to the substrate depth and are unreasonably high. While positive impacts are reported in green roofs with a substrate layer thickness of 4 – 5 cm, green roofs with substrate depth under 10 cm are not considered a green area in any of the reviewed ordinances. One municipality considers green roofs with substrate 10-30 cm as a green area, under specific conditions. This paper provides a review of the stipulations of the Bulgarian local legislation against the existing data for the effects of green roofs with different substrate depths and outlines the need for amendment of the legislation and future research.