Analysis on LID for highly urbanized areas' waterlogging control: demonstrated on the example of Caohejing in Shanghai

Cost-effectiveness analysis of extensive green roofs for urban stormwater control in response to future climate change scenarios

Green roof, as a popular low impact development practice, has become important to mitigate adverse impacts of future climate change on urban stormwater. However, there is limited information regarding assessment of the effectiveness of green roofs in response to uncertain future climate change challenges. In this study, the validated model was used to simulate the reduction performance of green roofs on urban catchment outflow and assess their cost-effectiveness in response to design storms under climate change scenarios. Results showed that the median runoff volume of urban catchments increased by 12.5 %-14.6 % and 15.5 %-18.1 % and the median peak flow rate increased by 14.4 %-17.8 % and 17.9 %-22.1 % under SSP2-4.5 and SSP5-8.5 scenarios, respectively. This indicated the variability of runoff volume and peak flow changes for short return storm events caused by climate change was relatively high. Green roof implementation had reasonable mitigation effects on runoff volume and peak flow amplification in urban catchments caused by climate change. The median runoff volume reduction of green roofs for the 1-year storm was 15.2 % under SSP2-4.5 scenario. As rainfall intensity increased, the median runoff volume reduction of green roofs significantly declined to 5.6 % for the 100-year storm. However, the variations of runoff volume and peak flow reduction of green roofs were relatively smaller for longer return periods under climate change scenarios. Runoff reduction percentages of green roofs increased linearly with their implementation cost. The average value of the cost-effectiveness (C/E) index for green roofs was 91.2 %/million $ under base climate condition, and it decreased to 88.9 %/million $ and 88.4 %/million $ for SSP2-4.5 and SSP5-8.5 scenarios, respectively. The C/E values decreased with increasing storm return period, and the values were relatively lower in SSP5-8.5 scenarios. These results could help to understand the potential role of green roofs to mitigate the impacts of future climate change.

A Discussion on the Application of Terminology for Urban Soil Sealing Mitigation Practices

Soil sealing is one of the most serious environmental problems today regarding its impact on cities. This article presents an analysis of the different urban practices currently used to mitigate the effects of soil sealing in urban areas. The main typologies, characteristics, differences, similarities and objectives have been considered. The practices analyzed were SuDS (Sustainable Drainage Systems), LIDs (Low Impact Developments), BMPs (Best Management Practices), WSUD (Water Sensitive Urban Design), GI (Green Infrastructure), and NbS (Nature-based Solutions). To understand the impact of these terms, an analysis of their presence in the scientific literature over the last 10 years is carried out. The results indicate that the trend in the use of these terms is increasing, with the number of articles having doubled in the last 10 years. This indicates the importance that the problem of soil sealing has acquired in the world, and the relevant environmental benefits of addressing it.

Sustainable Urban Drainage System (SUDS) modeling supporting decision-making: A systematic quantitative review

Decision Support Systems (DSS) for Sustainable Urban Drainage Systems (SUDS) are a valuable aid for SUDS widespread adoption. These tools systematize the decision-making criteria and eliminate the bias inherent to expert judgment, abridging the technical aspect of SUDS for non-technical users and decision-makers. Through the collection and careful assessment of 120 papers on SUDS models and SUDS-DSS, this review shows how these tools are built, selected, and used to assist decision-makers questions. The manuscript classifies the DSS based on the question they assist in answering, the spatial scale used, the software selected, among other aspects. SUDS-DSS aspects that require more attention are identified, including environmental and social considerations, SUDS trains performance and criteria for selection, stochasticity of rainfall, and future scenarios impact. Suggestions for SUDS-DSS are finally offered to better equip decision-makers in facing emerging stormwater challenges in urban centers.

Urban Planning and Design for Building Neighborhood Resilience to Climate Change

The aim of the paper was to present the procedure of building neighborhood resilience to climate threats, embedded in planning (from the strategic to local level) and design process and focused on usage of natural adaptive potential. The presented approach encompasses: (1) the strategic identification of focal areas in terms of climate adaptation needs, (2) comprehensive diagnosis of local ecological vulnerability and natural adaptive potential to build adaptive capacity, and (3) incorporation of natural adaptive potential through an identified set of planning and design tools. For diagnosis and strategic environmental impact assessment, the multicriteria analysis has been elaborated. The described procedure is applied to the City of Warsaw on the strategic level, by elaboration of the ranking of districts in terms of priority to take adaptation actions based on climatic threats, demographic vulnerability, and assessment of Warsaw Green Infrastructure potential. For further analysis at the planning and design stage, the district with the most urgent adaptation needs has been chosen, and within its borders, two neighborhoods (existing and planned one) with diagnosed ecological sensitivity were selected. Both case studies were analyzed in terms of environmental conditions, urban structure, and planning provisions. It enabled identification of existing natural adaptive potential and assessment of its use. As a result, propositions for enhancing neighborhood resilience to climate change were suggested.

Knowledge, attitudes, intentions, and behavior related to green infrastructure for flood management: A systematic literature review

Green infrastructure (GI), which mimics natural hydrological systems, is a promising solution for flood management at the intersection of urban built infrastructure and natural systems. However, it has not yet achieved widespread uptake, due in part to insufficient understanding of human dimensions of the broader socio-ecological-technical system. We therefore conducted a multidisciplinary systematic literature review to synthesize research on people's existing knowledge about flood risk and GI, and how that shapes their attitudes and motivation to adopt new solutions. We systematically screened 21,207 studies on GI for flood management; 85 met our inclusion criteria. We qualitatively analyzed these studies to extract results on knowledge, attitudes, intentions, and behavior relating to GI for flood management. Overall, knowledge of GI was low across the 44 studies in which it was evaluated. Seventy studies assessed attitudes about GI, including the functional, aesthetic, health and safety, recreational, conservation, financial, and cultural value of GI, albeit their measurement was inconsistent. Willingness to implement or pay for GI varied considerably across 55 studies in which it was measured. Twenty studies measured and documented behavior relating to GI use, and these found low rates of adoption. Few studies systematically assessed the role of demographic, socio-economic, or geographic characteristics that could influence individuals' knowledge, attitudes, intentions or behavior, and thereby the success of GI programs. We recommend that researchers should more systematically capture data on human dimensions of GI (i.e. knowledge, attitudes, intentions, and behavior) across diverse settings to improve program design and uptake, especially among vulnerable populations. Greater attention to the social component of the socio-ecological-technical system will help ensure that GI programs are equitable, inclusive, and sustainable.

Novel design of volume of detention tanks assisted by a multi-source pollution overflow model towards pollution control in urban drainage basins

The commonly employed design of detention tanks cannot effectively control overflow pollution because of non-stormwater entry and sewer sediments in the urban drainage system. Herein, a multi-source overflow model considering both overflow water quality and quantity has been developed for simulating real overflow events. Subcatchment and drainage information is extracted through geographic information system (ArcGIS) and a multi-source overflow model is developed in Stormwater Management Model (SWMM) by coupling runoff mode, non-stormwater mode, and sediment mode. This model is successfully calibrated and validated with the reasonable root-mean-square error (RMSE) of 8.2 and 5.8% for water quality and quantity, respectively. The simulated results suggest that the misconnected non-stormwater entry can affect overflow contaminant concentrations over the period of overflow due to its continuous pollution, while sewer sediments mainly exert effects on the peak pollution period of overflow. Based on model prediction, an approach called overflow peak pollution interception (OPPI) is proposed for model application and design optimization. The OPPI designed detention tank is suitable for high non-stormwater entries and long antecedent dry days (large amount of sediment). A case study is conducted in a high-density urban area of Shanghai, and compared with two commonly employed design methods in Germany and China, which have the similar design principle of volume, relying on amount of precipitation multiplying area of region, the combination of overflow model and OPPI approach enables to offer more accurate and effective design of detention tanks for pollution control in urban areas. Graphical abstract .

Application of SWMM 5.1 in flood simulation of sponge airport facilities

Construction of an airport runway makes the impervious area of the airport high, which leads to the deterioration of the water environment and frequent waterlogging disasters. The selection of sponge airport facilities (e.g., pump, multi-functional storage tanks, green roof) to mitigate airport flooding has been a crucial issue in China. This study aims to develop a conceptual rainwater-runoff simulation model, which can take into account the effects of such facilities of a sponge airport. Taking catchment N1 of Beijing Daxing Airport as a case study, SWMM 5.1 was implemented to develop three sponge airport models (one pump, two pumps, combination of pump and multi-functional storage tanks). A sensitivity analysis was carried out to guarantee the robustness of the developed models. A 1-hour rainfall scenario with a 5-year return period was employed on the three sponge airport models. The results showed that the effect rankings of the control strategies on the water depth, volume and peak inflow of catchment N1 were comparable - combined strategies (combination of pump and multi-functional storage tanks) > one pump and two pumps. The conceptual and hydrological models developed in this study can serve as a simulation tool for implementing a real-time rainwater drainage control system in Beijing Daxing Airport.

Synthesized trade-off analysis of flood control solutions under future deep uncertainty: An application to the central business district of Shanghai

Coastal mega-cities will face increasing flood risk under the current protection standard because of future climate change. Previous studies seldom evaluate the comparative effectiveness of alternative options in reducing flood risk under the uncertainty of future extreme rainfall. Long-term planning to manage flood risk is further challenged by uncertainty in socioeconomic factors and contested stakeholder priorities. In this study, we conducted a knowledge co-creation process together with infrastructure experts, policy makers, and other stakeholders to develop an integrated framework for flexible testing of multiple flood-risk mitigation strategies under the condition of deep uncertainties. We implemented this framework to the reoccurrence scenarios in the 2050s of a record-breaking extreme rainfall event in central Shanghai. Three uncertain factors, including precipitation, urban rain island effect and the decrease of urban drainage capacity caused by land subsidence and sea level rise, are selected to build future extreme inundation scenarios in the case study. The risk-reduction performance and cost-effectiveness of all possible solutions are examined across different scenarios. The results show that drainage capacity decrease caused by sea-level rise and land subsidence will contribute the most to the rise of future inundation risk in central Shanghai. The combination of increased green area, improved drainage system, and the deep tunnel with a runoff absorbing capacity of 30% comes out to be the most favorable and robust solution which can reduce the future inundation risk by 85% (±8%). This research indicates that to conduct a successful synthesized trade-off analysis of alternative flood control solutions under future deep uncertainty is bound to be a knowledge co-creation process of scientists, decision makers, field experts, and other stakeholders.

Simulating the effects of low impact development approaches on urban flooding: a case study from Tehran, Iran

Low impact development (LID) methods have been shown to be efficient in reducing the peak flow and total volume of urban stormwater, which is a top priority for effective urban stormwater management in many municipalities. However, decision-makers need information on the effects of LIDs and their associated costs before allocating limited resources. In this study, the Storm Water Management Model (SWMM) was used to investigate the effects of five different LID scenarios on urban flooding in a district in Tehran, Iran. The LID scenarios included rain barrel (RB) at two sizes, bio-retention cell (BRC), and combinations of the two structures. The results showed that significant node flooding and overflow volume would occur in the study area under the existing conditions, especially for rainfall events with longer return periods. BRC and combinations of BRC and RBs were the most effective options in reducing flooding, while the smaller-size RB was the cheapest alternative. However, normalized cost, obtained through dividing the total cost by the percent reduction in node flooding and/or overflow volume, was smallest for BRC. The results of this study demonstrate how hydraulic modeling can be combined with economic analysis to identify the most efficient and affordable LID practices for urban areas.

The influence of climate on the effectiveness of low impact development: A systematic review

Low impact development (LID) has been increasingly practiced since its emergence in the 1990s. Although the hydrological benefits of LIDs have been extensively documented, the climate impact on LID performance remains unclear with increasing variations in spatial and temporal climate patterns. This systematic review contributes to providing a structured summary of research on how LID systems are sensitive to climate variability by empirical and hypothetical research approaches. The selected 46 peer-reviewed journal articles published between 2003 and 2017 were analyzed by key variables, including climatic factors, LID types, and hydrologic measures used to quantify LID performance. A conceptual framework formulated in this study synthesizes the relationship between climate and LID effectiveness. The results of weighted meta-analysis reveal a greater sensitivity of runoff volume to changing storm frequency than peak discharge rates, while the capacity of LID systems to reduce both volume and peak discharge rates diminishes with increasing storm intensity. Future explorations of the sensitivity of LIDs to climate fluctuations will help strategize LID installation for targeted storm patterns and flood mitigation goals. To enhance existing methods and make a balance between empirical and hypothetical knowledge, this study suggests future directions of research and encourages development of effective stormwater management policy.

Extending the Rational Method for assessing and developing sustainable urban drainage systems

Onsite runoff control is considered an important part of sustainable urban drainage schemes, but estimating the maximum runoff flow rate from a catchment with onsite runoff controls remains controversial. Runoff controls complicate the issue by dividing the catchment into several subcatchments that feed into individual runoff controls, which dynamically regulate the catchment imperviousness. Rational Method (RM) is the most-employed technique to determine maximum flow rates for designing urban drainage infrastructures, but it cannot handle such conditions. Nonetheless, it has advantages over alternative methods in terms of principle from the urban drainage design perspective. This work develops Rational Method Prime (RMP) that follows the basic principle of RM but instead recalculates catchment variables by taking into account runoff control effects and evaluates runoff control efficiencies by using two indices. RMP has three merits: (1) providing an integrated response of the whole catchment with runoff controls; (2) interpreting runoff control effects by plotting runoff flow rate-rainfall duration curves; (3) connecting the design of runoff controls and storm sewers that are based on different design principles and rainfall statistics. Case study results showed that runoff controls reduced peak flow rates by 5.83-91.6%, corresponding to reduction factors for return period of maximum flow rate from 0.04 to 0.76. Indeed, the original RM is based on four assumptions, which also cause its weakness, and there have been current methods to address 3 of them. RMP contributes to addressing the last assumption (i.e. constant catchment imperviousness), which finally allowing the evolution from RM 1.0 to 2.0.