Stormwater Management Systems Research Articles

Estimating Combined Effects of Climate Change and Land Cover Change on Water Regulation Services of Urban Wetlands in Valdivia, Chile

AbstractThe relationship between cities and wetland cover varies across the globe, with some cities converting wetlands to low‐ and high‐density urban cover and others preserving, conserving, or restoring wetlands, or constructing new ones. However, the scientific literature lacks studies relating changes in systemic flood risk in an urban stormwater management systems to changes in wetland cover. Furthermore, whether and how such relationships are affected by changing storm intensity under climate change is unknown. We present a case study on the effects of changes in urban wetland extent and storm intensity on flooding in an urban drainage system in Valdivia, Chile, under several co‐produced future scenarios and historical trends of development. We used data derived from stakeholder workshops and historical landcover to determine four plausible scenarios of urban development, plus one business‐as‐usual scenario, in Valdivia through the year 2080. Additionally, we used historical precipitation data and downscaled climate data to estimate event rainfall from extreme storms in the year 2080. We found that system flood volume and time the system was flooded increased with increasing wetland loss and rainfall volume. Mean rate and hour of peak discharge were unaffected by wetland loss. Infiltration's relative role in reducing flooding diminished as wetland loss increased. Cities may still experience dangerous and/or unacceptable flooding even with extensive wetland coverage and will likely need to pair conservation with additional improvements in their stormwater management systems and contributing watersheds.

Trade-offs Between Equity and Efficiency in Prioritizing Critical Infrastructure Investments: A Case of Stormwater Management Systems

Critical infrastructures in many countries face the problem of aging and, thus, require significant upgrades to continue serving their purpose for the next few decades, especially in the face of extreme weather events caused by global climate change. Given the urgent need for such improvements and the substantial funding gaps being experienced, prioritizing investments in critical infrastructures is a challenging task for governments. Furthermore, the need to assure equitable solutions, as well as to consider deep uncertainty due to climate change, adds to the complexity of the problem. We seek to address this complexity by developing a set of models that explicitly consider both horizontal and vertical equity, along with efficiency, in prioritizing stormwater infrastructure improvement projects. While horizontal equity seeks to provide equal resources to everyone, vertical equity aims to allocate relatively more resources to vulnerable groups who are disproportionately susceptible to shocks and are more likely to fall into chronic poverty. By differentiating between losses in horizontal equity and vertical equity due to efficiency considerations, the models provide a practical approach to find the right balance among efficiency, horizontal equity, and vertical equity. The initial models are then extended into regret-based optimization models to help address the issue of deep uncertainty. A case study of stormwater infrastructure improvement in the City of Miami is presented, through which the performance of the models is explored both with and without the projected sea-level rise scenarios. The findings highlight the value of the proposed approach in promoting equity while maintaining efficiency.

A deep dive into green infrastructure failures using fault tree analysis

Green Infrastructure has transformed traditional urban stormwater management systems by fostering a wide range of service functions. Despite their popularity, green infrastructure's performance can deteriorate over their lifecycle, leading to operational failures. The operation of green infrastructure has predominantly relied on reactive maintenance strategies. To anticipate malfunctions and enhance the performance of green infrastructure in the long run, failure data needs to be recorded so that deterioration processes and component vulnerabilities can be recognized, modelled and included in predictive maintenance schemes. This study investigates possible failures in representative GIs and provides insights into the most important events that should be prioritized in the data collection process. A method for qualitative Fault Tree Analysis using minimal cut sets are introduced, aiming to identify potential failures with the minimum number of events. To identify events of interest fault trees were constructed for bioswales, rain gardens and green roofs, for three groups of service function failures, namely runoff quantity control, runoff quality control and additional service functions. The resulting fault trees consisted of 45 intermediate and 54 basic events. The minimal cut set analysis identified recurring basic events that could affect operation among all three green infrastructure instances. These events are ‘trash accumulation’, ‘clogging due to sediment accumulation’, and ‘overly dense vegetation’. Among all the possible cut sets, events such as ‘plants not thriving’, ‘invasive plants taking over’, and ‘deterioration caused by external influences’ could potentially disrupt most of the service functions green infrastructure provides. Furthermore, the analysis of interactions between component failures shows vegetation and filter media layer failures have the highest influence over other components. The constructed fault trees and identified basic events could be potentially employed for additional research on data collection processes and calculating the failure rates of green infrastructure and as a result, contribute to a shift toward their proactive operation and maintenance.

Assessing the impacts of urbanization and climate change on urban drainage system

AbstractUrban flooding is one of the significant issues that many cities are dealing with to ensure sustainable development. Upgrading the drainage systems is a standard measure that engineers have often used to reduce the risk of flooding. Because of climate change and urbanization, stormwater management systems may be inadequate to convey generated overflow in their catchment, which results in severe flooding in many cities worldwide. This research investigates climate change and urbanization's influence on urban flooding by simulating the EPA Stormwater Management Model for drainage systems in an urban catchment in An Ha, Tam Ky, Quang Nam. The results showed that urbanization shortens the initial abstraction ability while climate change increases extreme rainfall and water levels of receiving sources. Additionally, the impacts are even more substantial when the high urbanization rate increases by more than 70%, together with climate change.

Conservation of Water Resources in a Botanic Garden

Water-resource challenges, encompassing both quality and quantity, pose significant threats to Florida’s ecosystems, especially in the face of climate change, rising sea levels, and rapid urbanization. This paper explores the innovative stormwater-management system implemented at Naples Botanical Garden as a model for addressing these challenges. The Garden’s approach, treating stormwater as a valuable resource, involves dry and wet retention areas, created lakes, and a unique River of Grass, mimicking natural ecosystems. This system not only mitigates flooding, but also effectively removes pollutants, recharges the aquifer, and provides a habitat for diverse wildlife. The paper emphasizes the economic, environmental, and social impacts of traditional stormwater-management practices in Florida. Naples Botanical Garden’s case serves as a guide for botanical gardens and zoos globally, showcasing the pivotal role these institutions can play in sustainable water-resource management. The collaborative design process involving landscape architects, engineers, and horticulturists ensures a holistic and aesthetically pleasing approach to stormwater management. The paper underscores the role of botanical gardens in promoting nature-based solutions, educating the public, and offering tangible steps for implementing similar systems worldwide. It can help guide regional adaptation strategies to manage stormwater as a resource.

Improving the Performance of Porous Concrete by Utilizing the Pumice Aggregate

The performance of porous concrete, widely used for storm-water management, can be compromised due to the limitations of conventional aggregates. This research investigates the potential of pumice aggregate, a lightweight volcanic material, to enhance the mechanical strength, durability, and permeability of porous concrete. A series of experimental tests were conducted to evaluate the effects of varying pumice aggregate content on the properties of porous concrete. The results demonstrate that the inclusion of pumice aggregate significantly improves the compressive strength, flexural strength, and freeze-thaw resistance of porous concrete. Moreover, the permeability of the concrete mixtures is enhanced, allowing for better storm-water infiltration. The favorable porous characteristics of pumice aggregate contribute to increased void content within the concrete, enhancing its water storage capacity and reducing runoff. These findings suggest that utilizing pumice aggregate can lead to the development of more sustainable and efficient porous concrete systems for storm-water management. The incorporation of pumice aggregate not only improves the mechanical and hydraulic performance of porous concrete but also offers environmental benefits by utilizing a lightweight and natural material. The findings of this research have significant implications for sustainable construction practices and the effective management of storm-water runoff.

Modeling benefits and tradeoffs of green infrastructure: Evaluating and extending parsimonious models for neighborhood stormwater planning

Green infrastructure is often proposed to complement conventional urban stormwater management systems that are stressed by extreme storms and expanding impervious surfaces. Established hydrological and hydraulic models inform stormwater engineering but are time- and data-intensive or aspatial, rendering them inadequate for rapid exploration of solutions. Simple spreadsheet models support quick site plan assessments but cannot adequately represent spatial interactions beyond a site. The present study builds on the Landscape Green Infrastructure Design (L-GrID) Model, a process-based spatial model that enables rapid development and exploration of green infrastructure scenarios to mitigate neighborhood flooding. We first explored how well L-GrID could replicate flooding reports in a neighborhood in Chicago, Illinois, USA, to evaluate its potential for green infrastructure planning. Although not meant for prediction, L-GrID was able to replicate the flooding reported and helped identify strategies for flood control. Once evaluated for this neighborhood, we extended the model to include water quality through the representation of dispersion and settling mechanisms for two pollutant surrogates—total nitrogen and total suspended solids. With the extended model, Landscape Green Infrastructure Design Model-Water Quality (L-GrID-WQ), we examined benefits, costs, and tradeoffs for different green infrastructure strategies. Bioswales were slightly more effective than other green infrastructure types in reducing flooding extent and downstream runoff and pollution, through increased infiltration and settling capacity. Permeable pavers followed in effectiveness and are suggested where spatial constraints may limit the installation of bioswales. Although green infrastructure supports both flooding and pollution control, small tradeoffs between these functions emerged across spatial layouts: strategies based on only curb-cuts better controlled pollution, while layouts that followed the path of water flow better controlled flooding. By illuminating such tradeoffs, L-GrID-WQ can support green infrastructure planning that prioritizes unique concerns in different areas of a landscape.

Stormwater Quantity and Quality Management Options in Rapidly Urbanizing Watersheds: The Case of Mbezi River Catchment in Dar Es Salaam-Tanzania

Over the past two decades there has been a growing worldwide concern about the ability of urban infrastructure systems to withstand the increasing impacts of urban population and climate change. Akin to similar concerns, the objective of this paper was to evaluate stormwater quantity and quality management options in rapidly urbanizing watershed of Mbezi River catchment in Dar es Salaam-Tanzania using field investigations, public meetings and GIS techniques. Analysis results of capacity quantification of the proposed stormwater management components indicate that stormwater harvesting alone can disconnect up to 12% of stormwater runoff stream generated in the study catchment. In addition to other components, the proposed landscape-based stormwater management system puts more emphasis on rainwater harvesting, stormwater retention and detention elements to decelerate runoff speed and enhance more residence time for the runoff not only to infiltrate, but also to evapotranspire, while improving the scenery and aesthetic quality of the environment altogether.

Policy, Institutions and Regulation in Stormwater Management: A Hybrid Literature Review

Policies, Institutions and Regulation (PIR) aspects matter for different sectors’ growth and inclusive sustainable development, but there is little information in the literature on how to evaluate the effects of PIR on management options and outcomes or, on how positive results PIR changes can bring. In terms of stormwater management systems, or urban drainage, PIR is also a controversial and absent matter. Multidisciplinarity, several actors, countless formal and informal rules, and strong contextual path dependence make the subject complex and intricate. Considering the enabling environment, an alignment between policies, institutions and regulations is required to achieve good results and provide sustainable services. This study conducted a hybrid literature review of peer-reviewed papers in this field to provide an overview of how researchers have been studying PIR relations. The gaps show that the understanding of the PIR is fragile, as an important element for analyzing of results to be achieved, including SDG6, the financing and obtaining funds, guarantees and grants for the execution, delivery, operation and maintenance urban stormwater services and infrastructure. The contribution of this review is not only about what exists, but also mainly about what does not exist, since the void keeps waiting to be filled.

Connectors as a Key to Efficient Storm Water Management System: An In-Situ Assessment of Residential Estates in Poland

Abstract Adaptation to climate change often aims to increase the ability of cities to retain water. In recent years, there has been a shift in the approach to managing storm water from traditional methods to nature-based methods, which view storm water as a valuable resource. This study conducted a systematic analysis of eleven contemporary housing estates that are commonly considered sustainable. The study aimed to identify the elements of rainwater management and determine whether these elements form a system. The research found that, in most cases, not all elements of a rainwater management system (RMS) were present. The housing estates in Gdańsk and Gdynia demonstrated some features of an RMS but were still incomplete due to missing elements such as channels and gaps in curbs that guide rainwater. The results suggest that the implementation of some elements of an RMS does not necessarily create a fully functional system. A fully effective RMS requires the integration of all necessary elements to allow water to flow between them.

Using stomatal conductance capacity during water stress as a tool for tree species selection for urban stormwater control systems

Improving our understanding of how different tree species function in urban stormwater management systems is important, as tree pits may provide a temporary reservoir for stormwater and as trees have the potential to actively reduce stormwater runoff by transpiration. While urban tree planting pits are increasingly used for short-term water storage during stormwater runoff events, this storage can have negative effects on both tree vitality and water removal capacity, since stress from waterlogging result in stomatal closure. However, sensitivity to water stress varies by species. It is therefore important to determine which tree species can maintain long-term vitality and continued transpiration even under water stress, and thus are suitable for such locations. Here, we studied how nine different tree species, varying in expected tolerance to water stress, were affected by short-term and seasonal waterlogging, in a greenhouse experiment. The seedlings (Magnolia x loebneri, Tilia tomentosa, and Sorbus torminalis – low water logging tolerance; Cercidiphyllum japonicum, Rhamnus cathartica, and Fraxinus ornus – medium water logging tolerance; Quercus palustris, Acer saccharinum, and Fraxinus pennsylvanica – high water logging tolerance) were exposed to two days, five days and seasonal waterlogging. The treatments reflected best practice (optimal), suboptimal and total lack of tree pit drainage, using Swedish standards. Stomatal conductance and leaf water potential were determined regularly over a period of 71 days, and morphological adjustments were registered. Four of the species were affected already after two days of waterlogging, with reduced stomatal conductance either during the waterlogging or immediately after, and only the most waterlogging tolerant species were unaffected by the five-day treatment. However, all plants survived waterlogging for almost 30 days before the estimated permanent wilting was reached in some plants. We suggest that tree species selection for stormwater management systems should consider the species’ capacity to maintain high stomatal conductance during waterlogging, as there were clear differences between species. The effectiveness of the selected species could have an important impact on the stormwater management capacity of cities, as well as on other aspects of ecosystem service delivery from urban trees.

Urban ecosystem services and climate change: a dynamic interplay

Urban ecosystems play a crucial role in providing a wide range of services to their inhabitants, and their functioning is deeply intertwined with the effects of climate change. The present review explores the dynamic interplay between urban ecosystem services and climate change, highlighting the reciprocal relationships, impacts, and adaptation strategies associated with these phenomena. The urban environment, with its built infrastructure, green spaces, and diverse human activities, offers various ecosystem services that enhance the wellbeing and resilience of urban dwellers. Urban ecosystems offer regulatory services like temperature control, air quality upkeep, and stormwater management, plus provisioning like food and water. They also provide cultural benefits, promoting recreation and community unity. However, climate change poses significant challenges to urban ecosystem services. Rising temperatures, altered precipitation patterns, and increased frequency of extreme weather events can disrupt the functioning of urban ecosystems, impacting the provision of services. Heatwaves and urban heat island effects can compromise human health and energy demands, while changes in rainfall patterns can strain stormwater management systems and lead to flooding. Moreover, climate change can disrupt biodiversity and ecological processes, affecting the overall resilience and sustainability of urban ecosystems. To address these challenges, cities are adopting various adaptation strategies that recognize the interdependence between urban ecosystems and climate change. Green infrastructure interventions, such as the creation of urban parks, green roofs, and community gardens, aim to mitigate the impacts of climate change by enhancing the regulation of temperature, improving air quality, and reducing stormwater runoff. Additionally, urban planning and design approaches prioritize compact and walkable neighborhoods, promoting public transportation and reducing reliance on fossil fuels. Furthermore, engaging communities in the management of urban ecosystems and climate change adaptation measures is crucial for ensuring equitable distribution of ecosystem services and building social resilience. Therefore, the review article highlights a comprehensive understanding of the dynamic interrelationship between urban ecosystem services and climate change and their implications. By recognizing and integrating the contributions of urban ecosystems, cities can develop sustainable and resilient strategies to mitigate and adapt to climate change, ensuring the wellbeing and habitability of urban environments for present and future generations.

Policies, institutions, and regulations: PIRs of a stormwater management system.

Urban services, like stormwater management, are complex tasks that depend on many actors and involve activities that fall within several fields of knowledge, but infrastructure solutions have been known for a long time. Recently, the view that urban water should be treated in an integrated way has become more pronounced, breaking the pathway dependency that treated it in isolation. Since the last decade, the perception that policies, institutions, and regulations (PIRs) condition good results has become more pronounced. The key question lies in incentives capable of mobilizing actors to produce aligned PIRs in a governance system. Better results can come from transformations in the incentives that currently exist for PIRs. The compatibility between incentives, which are not always identical for all involved, aligning them toward results, is the main objective. Based on these premises, aspects related to the necessary ideological change are analyzed here, that is, at the level of ideas and conceptions, which reflect the perception of objective, involving all actors, public and private, attracting them to solve the challenges posed, for example, the delivery of services according to sustainable development goals (SDGs). Examples of this in-progress transformation, a paradigm shift, are presented as support for reflection and experimentation.

From flood paths to floodways, an efficient method to map, identify and evaluate suitable floodways: A case study from Trondheim, Norway

Due to climate change and rapid urbanisation, many Norwegian cities and urban areas suffer from pluvial flooding caused by intense rainfall exceeding the capacity of the stormwater management system. This results in increased runoff rates, volumes and peak flows in the drainage network. In response to these challenges, the authors explore the potential of utilising the urban surface's ability to transport floodwater as an integral component of the stormwater infrastructure. When the capacity of the stormwater drainage system is exceeded, the overland flow paths transporting floodwater are considered a part of the stormwater management system, as floodways. The study proposes a spatial GIS method to map existing drainage lines and identify existing surface areas that function as floodways, combined with an automated process to identify which drainage lines could be implemented as stormwater management measures. Critical points are introduced to assess the floodways' potential hazards, combined with a classification method to evaluate and sort floodways. A case study from Trondheim, Norway, was used to demonstrate how drainage lines can be identified as floodways using the proposed method. The case study is also used to illustrate how a GIS-based analysis can be extended from identifying to evaluating floodways and whether GIS is sufficient for floodway evaluation. The method enables urban planners and municipalities to identify which areas of the urban surface already function as floodways during extreme events, and to prioritise measures to secure such areas and increase the city's flood resilience. The results highlight the need to assess existing areas that function as floodways, and to implement and design needed areas as floodways. GIS-based methods combined with an evaluation scheme can be an adequate tool to map and evaluate floodways in urban areas. When using GIS-based methods, however, the corresponding hazard potential, and also the uncertainty of the floodway's spatial placement, should be considered.

Green roof as a passive cooling technique for the Mediterranean climate: An experimental study

Urban areas are undergoing increasing growth and land consumption. Through sustainable design and strategies, the built environment can contribute to mitigating the pressure on urban systems. To this aim, passive strategies can be integrated into buildings to improve their performance and that of the entire urban infrastructure system. Green roofs are among the most encouraged passive strategies, which can be added to both new and existing buildings. Green roofs reduce the Urban Heat Island effect, keeping the building and the city cooler; contribute to the stormwater management system, reducing runoff-flooding risk. However, while these advantages have been studied extensively, the actual cooling potential from evapotranspiration of green roofs has not been the subject of many studies. This work investigates the passive cooling potential of green roofs by evaporation through preliminary experimental studies on two green roofs. In greater detail, we aim to disentangle the substrate layer’s peculiar role, without vegetation, during both a simulated extreme rainfall event and regular irrigation regime, and we compare it to the performance of a gravel-composed reference roof, whose performance with respect to cooling is already good. Results demonstrated that the green roof without vegetation can cool down the roof, and the intense rainfall event was the one that provided the highest thermal performance to the roof.

Heterocypris incongruens maintains an egg bank in stormwater habitats and influences the development of larval mosquito, Culex restuans.

Dormant propagules can provide a rapid colonization source for temporary aquatic habitats and set the trajectory for community dynamics, yet the egg banks of stormwater management systems have received little attention. We asked which species hatched from the sediment of drainage ditches in Champaign County, IL, and found bdelloid rotifers and ostracods (Heterocypris incongruens) to be the most common taxa. These sites also are colonized by mosquitoes, and we established laboratory experiments to examine interspecific interactions between common co-occurring taxa. Culex restuans larvae were reared in the presence or absence of H. incongruens at two intra- and interspecific densities (20 or 40 total individuals) and their survivorship to adulthood, development time to adulthood, adult body size, and sex ratio were determined. Survival for Cx. restuans was significantly lower at high larval density than at low larval density in both treatments. Culex restuans larvae reared in the presence of H. incongruens had a shorter development time to adulthood and emerged as larger adults compared to those reared in the absence of H. incongruens. The sex ratios in the H. incongruens treatments were female-biased whereas those in the Culex-only treatments were male-biased. These differences may have epidemiological implications, as only female mosquitoes serve as disease vectors. Our results emphasize the importance of understanding interspecific interactions in influencing larval mosquito development traits.

Environmental impacts and cost analysis of low impact developments in arid climate: A case study of okanagan Valley (Canada)

Low impact developments (LIDs) are becoming increasingly popular in North America as viable solution for sustainable runoff management. Although hydrological performance of LIDs in relation to climates is readily available, there is still a gap on the evaluation of environmental and economic impacts of these infrastructures. We have evaluated the cradle-to- site lifecycle environmental and economic impacts of four LIDs using a case study of the stormwater management system at UBC Okanagan campus in BC, Canada. The environmental impacts and costs are determined via ReCiPe, TRACI, and net present value (NPV) method, respectively, and incorporated to obtain eco-efficiency of these LIDs. We found that the box planter and naturally occurring wetland on campus are the best LIDs with lower impacts (approximately 2.5% of the total impacts) than other LIDs. The cost savings from wetland are enormous due to zero construction and periodic maintenance after every five years. The box planter and wetland occupy the most favorable quadrant III of the eco-efficiency matrix whilst, bioswales and rain gardens are found in quadrant IV and I, respectively. When compared to the constructed wetland, an increase in the economic impacts is found without any influence on the eco-efficiency of the overall placement on eco-efficiency matrix. The maintenance phase contributes more to environmental impacts than the construction, whereas the life cycle cost analysis shows the opposite.

A New Method for Selecting the Geometry of Systems for Surface Infiltration of Stormwater with Retention

The application of infiltration basins and tanks is one of the primary means of sustainable stormwater management. However, the methods currently used to size these facilities do not take into account a number of parameters that have a significant impact on their required capacity. In light of this, the aim of this research was to develop a new method for selecting the geometry of the infiltration basins and tanks. Its application in the initial phase of designing stormwater management systems will allow assessing the validity of using such facilities in a given catchment area. This paper also presents the results of local and global sensitivity analyses examining how changes in individual design parameters influence stormwater infiltration facilities. The effectiveness of the developed model was evaluated through the example of a real urban catchment. The study was based on a hydrodynamic analysis of more than 3000 model catchments. The research plan was developed using Statistica software. On the other hand, the analysis of the results of hydrodynamic simulations was made possible through the use of artificial neural networks designed using the Python programming language. The research also confirmed that parameters such as the total catchment area, the percent of impervious area, and the type of soil within the catchment are crucial in the design process of these facilities. The results of this research can be considered when designing infiltration basins and tanks under Polish conditions. The described algorithm can also be used by other researchers to develop similar models based on different rainfall data. This will contribute to increasing the safety of urban infrastructure.

Modification of the "green" roof using technical solutions to reduce the negative impact of stormwater in urban conditions

The effectiveness and shortcomings of the "green" roof in the management of rainwater in the urban environment are analyzed. The scheme of the construction of a typical "green" roof and its classification in terms of types are shown. The proposal to increase the efficiency of stormwater management with the help of "green" roofs, through their integration with other systems, that is, the creation and implementation of "hybrid green roofs" (Hybrid Green Roofs), is substantiated. The possibility of a "blue" roof as a rainwater management technology without vegetation, which allows for effective retention of rainwater, is analyzed. The design scheme and principle of operation of the "green-blue" roof are given, and a comparative analysis of its effectiveness in stormwater management with traditional and "green" roofs is made. The results of research are presented, which showed that the measured runoff of rainwater from a "blue" roof is about 0.45 dm3/s compared to a regular roof with a runoff volume of 1.55 dm3/s. On the other hand, the runoff from the "green-blue" roof is about 0.1 dm3/s, compared to the control roof (0.3 dm3/s). It is substantiated that a "green-blue" roof is more effective in retaining rain runoff during long-term precipitation than a "blue" roof. However, both options can be applied to urban buildings as effective methods of managing stormwater runoff in urban areas. The scheme of construction and the principle of operation of the "purple" roof is given - as a type of roof that includes a spongy layer of hydrophilic mineral wool, a dense layer of polyester fabric, and can include an additional cellular layer to increase the amount of rainwater that can be retained, thereby reducing peak flow up to 95%. The results of the study are presented, which confirm the technical feasibility of the "purple" roof technology in terms of slowing down the flow and reducing the volume of storm water during rainfall of various intensities. A "Purple" roof, based on the concept of "storage", is conceptually and technically different from a "green" roof and can effectively delay peak rainfall, thereby reducing the pressure on the local stormwater management system. Unlike a "green-blue" roof, a "purple" roof is passive in nature - water flows off without any mechanical drainage points to divert the water. A diagram characterizing the degree of retention of rainwater, depending on the intensity of precipitation, by different types of roofs is presented. The authors proposed a comparative analysis of rainwater runoff management using traditional roofs, "green" roofs, and roofs modified with other "green" roof systems.

Estimation of extreme precipitation events in Estonia and Italy using dual-polarization weather radar quantitative precipitation estimations

Abstract. Evaluating extreme rainfall for a certain location is commonly considered when designing stormwater management systems. Rain gauge data are widely used to estimate rainfall intensities for a given return period. However, the poor spatial and temporal resolution of operational gauges is the main limiting factor. Several studies have used rainfall estimates based on weather radar horizontal reflectivity (Zh), but they come with a great caveat: while proven reliable for low or moderate rainfall rates, they are subject to major errors in extreme rainfall and convective cases. It is widely known that C-band weather radar can underestimate precipitation intensity due to signal attenuation or overestimate it due to hail and clutter contamination. From the late 1990s, dual-polarization weather radar started to become operational in the national surveillance radar network in Europe, providing innovative quantitative precipitation estimation (QPE) based on polarimetric variables. This study circumvents Zh shortcomings by using specific differential-phase (Kdp) data from operational dual-polarization C-band weather radars. The rain intensity estimates based on a specific differential-phase data are immune to attenuation and less affected by hail contamination. In this study, for the first time, QPEs based on polarimetric observations by operational C-band weather radars and without any rain gauge adjustments are analyzed. The purpose is to estimate return periods for 1 h rainfall total computed from polarimetric weather radar data using non-adjusted QPEs based on R(Zh,Kdp) data and to compare the results with those derived using R(Zh) and rain gauge data. Only the warm period during the year is considered here, as most of the extreme precipitation events for such a duration occur for both places studied (Italy and Estonia) at this time. Limiting the dataset to warm periods also allows us to use the radar-based rainfall quantitative precipitation estimations, which are more reliable than the snowfall ones. Data from operational dual polarimetric C-band weather radar sites are used from both Italy and Estonia. Given climatologically homogeneous regions, this study demonstrates that polarimetric weather radar observations can provide reliable QPEs compared to single-polarization estimates with respect to rain gauges and that they can provide a reliable estimation of return periods of 1 h rainfall total, even for relatively short time series.