Runoff Retention Research Articles

The potential of runoff retention structures as a strategy to control urban gullying in tropical cities

The potential of runoff retention structures as a strategy to control urban gullying in tropical cities

Flood prevention benefits provided by Canadian natural ecosystems

The escalating impacts of climate change have heightened concerns about the frequency and severity of natural disasters, particularly extreme flooding events. Future projections underscore the necessity for innovative flood prevention strategies, including broad-scale nature-based solutions. Here, we present the first comprehensive assessment of the flood prevention benefits provided by Canadian natural ecosystems and identify key areas crucial for human well-being. Using spatially explicit modeling, we (1) evaluated the potential runoff retention by natural ecosystems and (2) identified downstream urban and agricultural areas critically dependent on these natural benefits, particularly those in floodplains and close proximity to upstream natural ecosystems. The natural ecosystems within the top 5 % of sub-basins, representing regions with a high priority for conservation practices aimed at flood prevention, play a crucial role in safeguarding approximately 54 % (∼6,000 km2) of the total built-up area and 74 % (∼16,900 km2) of the total cropland situated within floodplains. Additionally, they are positioned upstream of floodplain-based urban zones belonging to 358 population centers, directly benefiting 3.7 million people (∼10 % of the Canadian population) and indirectly benefiting almost 20.1 million people (∼56 % of the Canadian population). Moreover, among Canada’s 5.2 million km2 of flood-preventing natural ecosystems, we identified a small fraction (10 %) whose loss or degradation would result in a significant (>50 %) increase in runoff. Several of these crucial ecosystems are situated in less populated northern regions, where local governments might want to incentivize conservation initiatives to support flood prevention. Our research underscores the imperative to integrate nature-based solutions into national strategies that consider the results of spatial planning analyses. Establishing other effective area-based conservation measures in the priority regions highlighted in this study can contribute towards reaching current ambitious environmental goals and provide critical flood prevention benefits. Additionally, our methods are transferable to other regions worldwide, leveraging globally available datasets and ensuring computational feasibility.

How vertical drainage positions of extensive green roofs affect the runoff control performance

The capacity of extensive green roofs (EGRs) in runoff reduction and pollutants control significantly decreased with increasing rainfall intensity. This is attributed to most of EGRs are the lower-drainage method and use a thinner substrate layer because of the structural load-bearing limits of buildings. Existing solutions depend on increasing the rainwater storage by thickening the substrate layer of EGRs, or replacing the substrate materials. We propose to enhance the water retention capacity of EGRs by adjusting vertical drainage positions and moving the lower-drainage at the bottom to upper-drainage over the substrate layer. To test the runoff control performance of EGRs with the upper-drainage method, we designed three EGR models with two different (upper- and lower-) drainage methods based on the common EGR’s structure in practice and carried out total 48 experiments under different rainfall intensities with an artificial rainfall simulator. The experimental design also included adjusting structural factors of the EGR to further explore the influences of roof slope, status of vegetation growth (height and canopy cover ratio), and model size. The average runoff retention rate for the upper-drainage EGR was 61.82 %, which was much higher than the 23.94 % for the lower-drainage EGR. The concentrations of TN and TP in runoff with the upper-drainage were 2.83 and 0.18 mg/L, which were much lower than the 8.47 and 2.10 mg/L for the lower-drainage EGR. EGRs with upper-drainage overall performed better in runoff control than EGRs with lower-drainage. Vegetation height and model size did not significantly affect the rainwater control performance for different drainage methods, while the change of slope affected the rainwater interception of the EGRs with upper-drainage method.

Impact of soil and water conservation structures on the spatial variability of topsoil moisture content and crop productivity in semi-arid Ethiopia

Plant available soil moisture and its spatial variability is among the most important limiting factors for crop and livestock productivity in semi-arid Ethiopia. The objectives of this study were therefore: 1) to measure the effects of land use and slope gradient on spatial variability of topsoil moisture content. 2) to analyze the variability of topsoil moisture content and crop responses under different soil and water conservation (SWC) structures and 3) to analyze whether topsoil moisture content, grain and biomass yields vary in relation to SWC structures. In total, 21 large runoff plots (600–1000 m2) were installed and treated with stone bunds, trenches, stone bunds with trenches and a control plot at each site. Plot sites were located on gentle (5%), medium (12%) and steep (16%) slopes of cropland and rangeland. Topsoil (0–15 cm) moisture content for plots were monitored daily using soil moisture probes (Theta-Probes) and weekly using manual sampling over two growing seasons. Crop performance was monitored during two growing seasons and grain and biomass yield were measured at harvest. Results show that average gravimetric moisture content of the topsoil during growing seasons is remarkably higher for cropland (33–25 g/100 g) compared to rangelands (24–20 g/100 g). This is due to tillage-induced runoff retention and infiltration. Soil moisture content decreases with increasing slope gradients, owing to increased drainage. Considering the effects of SWC structures, average topsoil moisture contents at accumulation and erosion zones are generally higher as compared to middle zone between two successive SWC structures. Average seasonal volumetric soil moisture content of 38.2 (cm3/100 cm3) in 2011 and 39.4 (cm3/100 cm3) in 2012 for accumulation zone of plots with stone bunds with trenchers are significantly higher than at other sampling locations. Crop growth performance, grain and biomass yield varied among plots and depended on slope gradients and SWC structures. Grain yields of wheat in 2011 and barley in 2012 were significantly higher for plots with SWC structures as compared to control plots and are highly correlated to topsoil moisture content (r = 0.64; p < 0.04 in 2011 and r = 0.59, p < 0.01 in 2012). Even when taking into account the cropland area occupied by SWC structures, grain yield increased by (4.2%−33%) for plots with SWC structures as compared to control plots. Overall, our results show that implemented measures may not only reduce runoff and soil loss, but also increase crop productivity by enhancing soil moisture and thus can significantly contribute to sustainability of agro-ecosystems in semi-arid environments.

Maximising runoff retention by vegetated landscape elements positioned through spatial optimisation

Ecosystem services provided by vegetated landscape elements (vLEs) are increasingly recognised. One of the services provided is the mitigation of downstream flood risk. Obviously, the type and spatial configuration of vLEs impact the magnitude and timing of the runoff retention. Hence policy programs focused on the conservation and restoration of vLEs would benefit from a capability to determine the optimal spatial configuration of vLEs leading to maximum impact for minimal cost.We integrated the Landlab rainfall-runoff model in an iterative spatial optimisation framework to deal with rasterised linear parcel boundaries whereby the cumulative capability to reduce discharge through the installation of vLEs is the ranking criterion. We applied the procedure to a 191 ha agricultural watershed situated in the Belgian Loess belt encompassing 34 km parcel boundaries.Our results demonstrated that discharge volume can be more effectively reduced when vLEs are implemented based on the priority ranking obtained through our approach compared to both a random positioning of vLEs of the same length and type and the existing vLE configuration. The priority parcel boundaries are mainly located along preferential flow paths, highlighting the importance of the upslope area associated with vLEs and the infiltration enhancement they provoke. The application potential of the optimisation approach is not limited to the topic of finding priority locations for vLEs to reduce discharge but can be applied in a variety of disciplines that require answering questions about the optimal spatial configuration of interventions.

Co-creating urban ecosystem accounting: Physical and monetary accounts of runoff retention service provided by urban green spaces

Urban ecosystem accounting can provide the structure for systematically integrating the value of urban green spaces into management and decision making to support urban resilience and sustainability. However, there are very few instructive examples of urban ecosystem accounting, particularly those created collaboratively with a municipality. Therefore, the aim of this study was to develop co-created urban ecosystem accounts using Tampere, Finland, as a case study. By discussing concrete political and planning-related needs, priorities, and data availability, this study identified urban flooding and the role of green spaces in alleviating this challenge as critical issues. An ecosystem extent account was compiled for accounting years 2012 and 2018 to quantify changes in the extent of ecosystem types. Additionally, an ecosystem service account (physical and monetary), for runoff retention, was compiled for the same years. The runoff retention service was quantified using the InVEST Urban Flood Risk Mitigation model, considering two precipitation events representative of rainstorms that trigger urban flooding. The runoff retention service was translated into service providing areas, which were used in conjunction with service demanding areas to estimate the physical terms of actual flows of retention service for accounting. The monetary value of the service was estimated using the avoided damage cost method. Between 2012 and 2018, the value of runoff mitigation service provided by green spaces increased by 7 % under the 24 mm scenario and by more than 40 % under the 50 mm scenario. The accounts showed concretely how important urban green spaces are in the City of Tampere, and provide an argument to preserve and even increase them in the urban structure. Our experiential ecosystem accounts for urban runoff retention service by green spaces also offer insights to other municipalities, encouraging them to take steps forward in ecosystem accounting.

Ecological Benefits and Plant Landscape Creation in Urban Parks: A Study of Nanhu Park, Hefei, China

Plant landscape creation in urban parks is an important aspect of urban ecological construction under the goal of “carbon neutrality”. In this study, the plant community of Nanhu Park in Hefei City was considered the research subject, and its tree species’ composition and diameter at breast height (DBH) were analyzed. The ecological benefits of the park’s green space were evaluated using the i-tree Eco model, and the carbon sequestration, runoff retention, air pollution removal, and oxygen production benefits were quantified as economic values and combined with the landscape effect evaluation method. The results show that Nanhu Park is rich in tree species types, with 5871 trees of 41 species in 23 families and 32 native species, among which three species of Sapindus mukorossi, Eucommia ulmoides, and Triadica sebifera accounted for 43.7% of the total number of trees. The dominant tree DBH was intermediate (7.6–15.2 cm). In Nanhu Park, the economic benefits were ordered as follows: carbon sequestration &gt; runoff retention &gt; air pollution removal &gt; oxygen production benefits. The dominant tree species strongly contributed to the total ecological benefit of urban park green space; the ecological benefit of individual trees was not positively correlated with the number of tree species; native tree species had better ecological and landscape effects, while plant communities with growth changes and hierarchical depth of landscape were more popular. The analysis of ecological benefits and landscape evaluation of urban park green space provide a theoretical basis for enhancing the plant landscape, thus providing a case reference for promoting the construction of park green space in Hefei.

Integrated evaluation and attribution of urban flood risk mitigation capacity: A case of Zhengzhou, China

Study regionThe Zhengzhou City in China Study focusUrban flood risk mitigation (UFRM) refers to the runoff retention capacity of land surface in urban regions. Previous studies have focused on assessing the UFRM change in central urban areas. Nevertheless, analysis of the UFRM change considering the heterogeneity of urban and rural gradient is scarce. This study aims to evaluate the spatiotemporal change of UFRM and its influencing factors in different urban functional zones. An integrated framework combining the hydrological model and geographic information system (GIS) has been established to assess the evolution of UFRM in Zhengzhou between 2000 and 2020. New hydrological insights for the regionThe findings illustrate the following: (1) The UFRM of Zhengzhou experienced a 10.76% increase from 2000 to 2010, followed by a subsequent 3.38% decrease from 2010 to 2020.(2) UFRM increased in ecological areas while decreasing in urban regions, revealing a disparity between UFRM supply and demand. (3) The adverse impact of impervious surfaces on UFRM surpasses the influence of precipitation intensity in urban regions. As a result, this study suggests that urban areas should avoid extensive expansion of impervious surfaces and prioritize implementing low-impact development practices. The ecological zones should implement rigorous policies to protect natural preservation. These findings provide policymakers a scientific foundation for devising sustainable urban development strategies to enhance urban flood resilience.

Small Island City Flood Risk Assessment: The Case of Kingston, Jamaica

Jamaica has had over 200 floods in the past 50 years, causing significant human and economic losses. Kingston has often caused the most damage due to its high population density and capital exposure. Kingston is crucial to the country’s socio-economic stability, and climate change is increasing flood risk, but a local-scale assessment of its flood risk is unavailable. This study fills this gap in the literature by using two models of the integrated Valuation of Ecosystem Services and Tradeoffs (inVEST) suite to qualitatively assess Kingston metropolitan pluvial and coastal flood risk. Key locations like Kingston Container Terminal and downtown Kingston are at high coastal flood risk, according to the results. The study also shows that sea level rise (117%) and habitat loss (104%) will increase the highly exposed area. Instead of hard-engineering coastal protection, this study suggests investing in nature-based and ecoengineering solutions to improve coastal resilience and ecosystem services. The urban flood assessment finds downtown, particularly the Mountview and Minor catchments, at high risk due to poor runoff retention and high population density. To fully address downtown pluvial flood risk, structural social reforms are needed. To reduce short-term flood risk, local authorities should consider targeted adaptation measures. These may include maintaining the drainage gully system and reducing surface runoff in uphill downtown areas. Thus, this study seeks to inform Kingston urban planners about risk distribution and suggest adaptation measures to improve flood resilience.

Runoff retention characteristics of forested and deforested catchments: an analysis using a spatially lumped model

ABSTRACT This study investigates the runoff characteristics of forested and deforested catchments using the Soil Conservation Services–curve number (SCS-CN) model from the perspective of the Kerala floods in 2018 and 2019. The forested and deforested catchments chosen for the study are the drainage area of the Kakkayam Dam and Punoor River respectively of Kozhikode District, Kerala. The study used input variables such as rainfall, land use/land cover (LU/LC) and soil data to estimate the runoff depth from these catchments during the floods in 2018 and 2019 using the SCS-CN model. Here, the hydrological response of these catchments is examined by different scenarios of rainfall and LU/LC change. It is found that the deforested catchment generates more runoff compared to the forested catchment under identical rainfall conditions. However, the study shows that, the runoff depth in the deforested catchment is expected to reduce if certain portion of plantations and barren land converts into the forest cover. The ability of runoff retention of the forested catchment is expected to lose if the forest-covered land is utilized for the plantation activities.

Assessment of urban ecosystem condition and ecosystem services in Shenzhen based on the MAES analysis framework

Rapid urbanization has led to a reduction in the capacity of urban ecosystems to provide essential services. Understanding the interplay between urban ecosystem condition (EC), ecosystem service (ES) capacity and environmental stress is important for achieving sustainable economic and social development. Taking Shenzhen, a representative region of rapid urbanization in China, as an example, this study analyzed the evolution of urban EC and spatial and temporal patterns of key ESs from 2000 to 2020. With reference to the Mapping and Assessment of Ecosystems and their Services (MAES) framework and its indicators, the analysis process used the InVEST model and empirical statistical methods. The spatial and temporal geographically weighted regression (GTWR) model was used to determine how the ESs responded to EC. The results demonstrated a tendency of increased environmental stress and degraded EC in the urban ecosystem during the study period. The supply of ESs was on the decline, with runoff retention and microclimate regulation showing significant declines, while noise reduction showed an upward tendency. ESs had an overall “east-high-west-low” spatial pattern. In terms of response relationships, the regulating and cultural services were mainly negatively correlated with PM10 concentration, temperature, and the percentage of construction land and positively correlated with vegetation cover. There was spatial and temporal heterogeneity in the mechanism of EC influence on specific services. The percentage of construction land was the key negative influencing factor, indicating that urban expansion exacerbates the decrease in the supply of ESs. The results of the study also provided evidence that the MAES analysis framework can accurately analyze environmental problems in urban ecosystems and offer a practical solution for urban ecosystem assessments. For the sustainable development of urban ecosystems, it is advised that the ES concept be included as a key decision factor in the development of urban planning policies.

Changes in Dissolved Inorganic Carbon Across Yangtze River Regulated by Dam and River‐Lake Exchange

AbstractThe boom in dam construction and continuous river‐lake exchange has had a profound impact on the transmission and transformation of riverine dissolved inorganic carbon (DIC). An in‐depth understanding of the change mechanisms of DIC concentrations and sources driven by dam operation and lake recharge is crucial for regulating greenhouse gas emissions and evaluating the impact of DIC on the global carbon cycle. This study investigated dam‐ and lakes‐driven DIC via the concentration and δ13C of DIC, combined with anions, cations, δD and δ18O in the main stream of the Yangtze River. DIC showed a decreasing trend from upper reach (2,262.31 ± 113.69 μmol kg−1) to lower reach (1,771.61 ± 89.36 μmol kg−1). Carbonate dissolution proportion (from 36.45% to 28.44%) and atmospheric CO2 proportion (from 37.51% to 22.94%) of DIC decreased from upper reach to lower reach, whereas soil CO2 proportion of DIC (from 26.01% to 48.63%) increased. The control of dam operation on DIC biogeochemical process was revealed from different time scales. From the perspective of short‐term seasonal changes (from 2020 to 2021), the mineralization of organic matter in the dry season strengthened CO2 degassing and calcite precipitation, reducing the DIC and increasing the proportion of soil CO2. Meanwhile, longer periods of runoff retention provided sufficient time for water–rock reactions in the wet season and increased the DIC and carbonate dissolution source in the reservoir area. On a long‐term scale (from 2009 to 2021), a decrease in pH driven by sediment mineralization contributed to an annual increase in DIC in the reservoir. The flow of lakes mixed into the mainstream was revealed by the enrichment of δ18O, and river‐communicating recharge decreased the DIC and carbonate dissolution source. We show that dam operation and lake inflow change DIC concentrations and sources and therefore need to be considered in the transmission and transformation processes of DIC in the river‐ocean continuum.

Comparisons of Retention and Lag Characteristics of Rainfall–Runoff under Different Rainfall Scenarios in Low-Impact Development Combination: A Case Study in Lingang New City, Shanghai

An increasing focus has been given to stormwater management using low-impact development (LID), which is regarded as a “near-nature” concept and is utilized to manage and reduce surface runoff during the rainfall–runoff process. According to the hydrological monitoring data, we evaluated the retention and lag characteristics of rainfall–runoff in LID combination under three rainfall-intensity scenarios (light–moderate, heavy, and torrential rainfall) in Lingang New City in Shanghai. LID facilities have been constructed for three years in the target study area, including rain gardens, retention ponds, green parking, porous pavement, and grass swales. The average runoff retention was 10.6 mm, 21.3 mm, and 41.6 mm under light–moderate, heavy, and torrential rainfall scenarios, respectively, and the corresponding runoff retention rate was 72.9%, 64.7%, and 76.1% during the study period. By comparing rainfall, runoff retention, runoff retention rate, cumulative rainfall, and lag times, it becomes evident that the ability to retain runoff can be greatly improved in the LID combination. The average runoff retention was significantly enhanced by nearly two times and four times under the heavy and torrential rainfall scenarios compared to the conditions under the light–moderate rainfall scenario. Furthermore, the lag time from the end of rainfall to the end of runoff (t2) and the lag time between the centroid of rainfall and the centroid of runoff (t3) showed a significantly negative correlation with rainfall intensity. Meanwhile, t3 presented an incredibly positive correlation with rainfall duration. In this study, the LID combination demonstrated superior benefits in extending the duration of runoff in rainfall events with lower rainfall amounts, and demonstrated significant overall lag effects in rainfall events with longer durations and lower rainfall amounts. These results confirmed the vital role of the LID combination in stormwater management and the hydrologic impact of the LID combination on rainfall-induced runoff retention and lag effects. This work has provided valuable insights into utilizing LID facilities and can contribute to a better understanding of how runoff retention and lag characteristics respond to different rainfall intensity scenarios.

Presentation of a Rainfall–Runoff Retention Model (3RM) Based on Antecedent Effective Retention for Estimating Runoff in Seven Basins in Iran

This study aims to correct and assess the SCS-CN model. In this research, the 3RM model (written by Shamohammadi) has been modified in such a way that the maximum primary retention (I), maximum secondary retention (Fmax), and basin potential retention (Smax) can be calculated using precipitation (Pa). The purpose of this study is to evaluate the total retention model (St=f(Fmax,Smax,pa)) and the runoff model (Q=f(St,pa)) using the mountain basins of Iran, including Emameh, Kasilian, Navrood, Darjazin, Kardeh, Khanmirza, and Mashin. The results showed that the primary retention, maximum secondary retention, and retention capacity are, respectively, 2.3, 30.4, and 32.7 mm in Imamah, 2.5, 48.6, and 51.1 mm in Kasilian, 2.4, 26.7, and 29.1 mm in Navrood, 3.2, 21.5, and 24.7 mm in Darjazin, 1.7, 15.0, and 16.7 mm in Kardeh, 2.5, 33.2, and 38.1 mm in Khanmirza, and 4.9, 44.5, and 50.6 mm in Mashine. Additionally, the λ (ratio of primary retention to potential retention) values for all basins are less than 0.2 (suggested by SCS) and vary between 0.05 in Kasilian and 0.1 in the Darjazin, Kardeh, and Mashine basins. The results of fitting the model to the rainfall-runoff data showed that the evaluation indices, including the coefficient of determination (R2), Nash–Sutcliffe (NS), and root mean square error (RMSE), for predicting the runoff in the basins varied between 0.78 to 0.96, 0.78 to 0.961, and 0.86 to 2.28, respectively. According to the obtained results, it can be concluded that the model has an acceptable ability to predict runoff for all the studied basins.

High water use plants influence green roof substrate temperatures and their insulative benefits

Green roofs are amongst the solutions employed to deliver sustainable buildings in cities. Their vegetation and substrate layers can reduce the heat transfer through the roof, thus potentially reducing energy used for building cooling and heating. However, little research has investigated the insulative properties of drought-tolerant plants which also have high water use. These plants have been found to improve runoff retention by removing larger volumes of water from the substrate through higher transpiration rates than succulents. This planting strategy may also enhance green roof cooling performance due to their greater evapotranspiration rates.In this study, the thermal performance of three drought-tolerant species with high water use — Lomandra longifolia, Dianella admixta, and Stypandra glauca — was evaluated and compared with a commonly used succulent species (Sedum pachyphyllum) and a bare unplanted module.L. longifolia had the best insulative performance during the entire investigated period, reducing green roof substrate surface temperature up to 1.86 °C compared to succulent S. pachyphyllum. In summer, the mixture reduced heat gain to a greater extent than monoculture plantings of all species except L. longifolia. Summer measurements also suggest that plants with high leaf area index (LAI) and higher albedo should be selected to reduce surface temperatures. High evapotranspiration rates of high water use L. longifolia led to greatest reduction of bottom surface temperatures during a heatwave when decreasing its water content from 18.5% to 2.9%. Results obtained using an analytical hierarchical partitioning technique indicated air temperature had the most significant impact on temperatures at both the surface of the planting substrate and the bottom of each green roof unit, accounting for 48% to 58% of the variation.

Performance assessment for the integrated green-gray-blue infrastructure under extreme rainfall scenarios

Synergistic allocation of urban stormwater infrastructure is critical to flood risk prevention and control under extreme rainfall events. This study focuses on the interaction regularity of green, gray, and blue infrastructure in the process of runoff retention and discharge under extreme rainfall scenarios. Three strategies, namely, gray infrastructure, green-gray infrastructure, and green-gray-blue infrastructure, are proposed to analyze the effectiveness of different scenarios on flood risk control capabilities of urban drainage systems and to determine the key influencing factors of the three strategies. The results show that green-gray-blue infrastructure demonstrates synergy in improving the efficiency of urban drainage systems. Under gravity drainage conditions, the backwater jacking caused by high river water levels has a certain impact on the smooth discharge of stormwater runoff in urban drainage systems. This case study identified a sensitive range in the influence of water level on runoff control and drainage function and an adaptive range in which the flood increases slightly with the water level increase. These present notable rules in improving the synergistic effect of blue infrastructure in the integrated urban green-gray-blue infrastructure system.

Inequity in nature’s contributions to people in Ōtautahi/ Christchurch: A low-density post-earthquake city

Nature’s contributions to people (NCP) include the regulating, material, and non-material benefits of urban vegetation that improve well-being. It is increasingly important to plan cities that provide multiple types of NCP equitably to all residents of the city. However, due to historical legacies and planning policies, it is common for the most socially and economically vulnerable urban residents to suffer reduced access to the benefits of urban ecosystems. Previous studies of urban NCP have drawn attention to inequity in one or several types of NCP, but few have analysed a broad range. Here we analysed inequity in nine diverse forms of urban NCP across an index of economic and social vulnerability designed specifically to characterise vulnerability to environmental pressures. Furthermore, we used spatial analysis to map co-variance in vulnerability and a composite indicator of urban NCP, thus highlighting priority regions for future investments in green infrastructure. We applied this approach to the city of Christchurch/ Ōtautahi in Aotearoa/ New Zealand, which provides a valuable case study due to its multicultural population and recent history of widespread damage and regeneration following the 2011 earthquake. Overall, the distribution of urban NCP is inequitable to the disadvantage of more vulnerable residents. Residents of more vulnerable neighbourhoods experienced reduced provision of carbon stock, runoff retention, air quality enhancement, shade, educational green space, public outdoor space accessibility, private green space, and bird biodiversity contributions. Conversely, more vulnerable neighbourhoods had greater provision of erosion mitigation (although negligible in magnitude). The wide range of indicators used and assessed in response to vulnerability, coupled with an assessment of the type of vegetation cover (i.e. grass, tall trees) provides greater insights into how inequities in urban NCP can be addressed in future redevelopment.

Analyses of the Effectiveness of Different Media Depths and Plant Treatments on Green Roof Rainfall Retention Capability under Various Rainfall Patterns

Green roofs have been used to reduce rainfall runoff by altering hydrological processes through plant interception and retention as well as detention within the green roof system. Green roof media depth, substrate type, plant type and density, regional climatic conditions, rainfall patterns, and roof slope all impact runoff retention. To better understand the impacts of media depth (10, 15, and 20 cm), plant (planted and non-planted), and rainfall pattern (low, medium, and high) on rainfall retention, we analyzed data collected between September 2005 and June 2008 from 24 green roof models (61 cm × 61 cm) for growing and non-growing seasons. Our results showed that a planted green roof has greater rainfall retention capability than a non-planted green roof for all media depths. Interestingly, a non-planted green roof system with a 10 cm media depth retained greater rainfall than a planted green roof during both growing and non-growing periods. Retention capability decreased with increasing rainfall amounts for both planted and non-planted green roofs and seasons (growing and non-growing). The 15 cm media depth green roof retained significantly greater rainfall depth than the 20 cm models during medium (0.64 to 2.54 cm) and high (&gt;2.54 cm) rainfall events for the growing season but not during the non-growing season. The study provides insight into the interactive effects of media depth, rainfall amount, plant presence, and seasons on green roof performance. The results will be helpful for designing economical and effective green roof systems.

Unmanaged vegetated roofs hydrological performance in subtropical areas: An investigation in São Paulo, Brazil

Extensive vegetated roofs are Nature-based Solution with the ability to manage rainwater runoff in densely built spaces. Despite the large amount of research demonstrating its water management abilities, its performance is poorly quantified under subtropical climates and when using unmanaged vegetation. The present work aims at characterizing the runoff retention and detention of vegetated roofs under the climate of São Paulo, Brazil, accepting the growth of spontaneous species. By using real scale prototypes under natural rain, a vegetated roof hydrological performance was compared with a ceramic tiled roof. By using models with different substrate depths under artificial rain, changes in the hydrological performance were monitored for different antecedent soil moisture contents. Results from the prototypes showed that the (i) extensive roof attenuated from 30 % up to 100 % the peak rainfall runoff; (ii) delayed the peak runoff from 14 up to 37 min and (iii) retained from 34 % up to 100 % the total rainfall. Furthermore, results from the testbeds indicated that (iv) when comparing two rainfalls with same depths, the one with longer duration can saturate more the vegetated roof and thus undermine more its ability to retain water; and (v) when not managing the vegetation, the vegetated roof's soil moisture content loses correlation with the substrate depth, as plants will also develop more and will more effectively restore the substrate retention capacity. Conclusions point to extensive vegetated roofs as a relevant sustainable drainage system in subtropical areas, but demonstrate that its performance is highly dependent on structural factors, weather factors and level of maintenance. Such findings are expected to be useful for practitioners dimensioning these roofs as well as for policy makers towards a more accurate standardization of vegetated roofs in subtropical regions and Latin American developing countries.

Long-term monitoring and modelling of pasture regeneration and water quality from a Bothriochloa pertusa site in the Great Barrier Reef catchments

There has been considerable investment in grazing land management in Australia’s Great Barrier Reef catchments targeted at improving off-site runoff and water quality. This study used a systems modelling framework to analyse an 18-year monitoring data set from an Indian couch (Bothriochloa pertusa) dominated hillslope flume site in the Burdekin catchment, Australia. The analyses show important functional differences in B. pertusa pastures, relative to the native tussock pastures they replaced, with implications for how they are monitored and managed: (1) rates of landscape recovery were far slower than rates of degradation. In the practical time frames of most land managers, transition to a B. pertusa state is effectively irreversible, so historical management practices will have to adapt; and (2) transformations in pasture composition and structure can lead to misinterpretation of monitored trends in ground cover (a common proxy for land condition). At 50% pasture cover, B. pertusa pastures have only 33% of the biomass of local tussock pastures. Where B. pertusa invasions are occurring, inferences from positive associations between changes in cover and landscape function can break down: increases in ground cover can instead be accompanied by decreases in biomass, productivity, and runoff retention. The paper contributes an initial calibration of the GRASP pasture grazing systems model for a transformed B. pertusa site, capturing the observed relationships between grazing management, pasture biomass, ground cover and water quality. This serves as a starting point from which these landscapes, of growing extent and concern in Great Barrier Reef catchments, can be better represented in monitoring and modelling assessments, and for revised management options to be explored. The calibrated model was able to accurately represent long-term average runoff and sediment yield (both within 2% of observed) but was only able to adequately represent the year-to-year variation in runoff (not sediment).