Within the global transition to sustainable urban water management, Dutch polder cities are also contemplating revitalising their water traditions. One of the keys to this task is to integrate water management into urban design, which is explored but not yet practically instrumentalized in the urban design process. This article introduces the concept of hybridity and develops a Hybridity Design Approach as an interdisciplinary methodology to explore the possibility of realising the extreme low impact Closed City Concept. Integration of the water environment and urban space needs interdisciplinary cooperation and sharing knowledge, as well as an innovative way of thinking about water-resilient urban design, maximising the landscape quality of a polder city while minimising its hydrological footprint in the region. Effective visualisation tools and techniques for this collaborative design process are developed and tested in the area of Zevenkamp in Rotterdam.@en

As the world grapples with the profound impacts of climate change, water scarcity has become a pressing issue. However, there is a shortage of in-depth research on the trade-offs between water resource dependence and the economic, ecological, and social needs of arid and semi-arid regions like Lanzhou, China. Flower cultivation in Lanzhou relies heavily on the Yellow River, often overlooking the potential of natural rainfall. Here we first calibrated a water balance model through artificial precipitation experiments in a Soil and Water Conservation Demonstration Park in Lanzhou. We then developed a multi-objective optimization model to balance the cost-benefit considerations of various plausible measures across economic, ecological, and social dimensions in the searching for solutions that are more adaptable to climate change and local development needs. Model simulations show that the solutions we designed can effectively manage water-shortage days, significantly reduce Yellow River water extraction, and improve cost-effectiveness, meeting 66%–80% of water needs for flower cultivation in the studied park. The findings highlight the potential of rainwater collection and utilization solutions to mitigate water scarcity in arid and semi-arid cities, thereby enriching water resource management.

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Urban water management is confronted with more frequent, more extreme weather events. This paper introduces the Three-Points Approach (3PA) into Sponge City concept, to create a novel framework aimed at guiding water management interventions across local, urban, regional, and river basin scales. The 3PA integrates three domains—Day-to-day, Design, and Extreme —offering a nuanced strategy for flood and drought risk mitigation, also for extreme events. Notably, the 3PA emphasizes the fusion of blue-green infrastructure (BGI) with conventional gray approaches to enhance both multifunctionality and resilience in extreme weather conditions. The study identifies critical issues of implementing this Three-Points Sponge Policy (3PSP) approach, including spatial and temporal scales, transitioning from gray to blue-green infrastructure, asset management, data handling, and effective communication. Interventions spanning various spatial scales and addressing flood protection, drought resilience, and water quality are explored in a first and indicative application in Zhengzhou. The case study distills key design principles, highlighting the imperative of never shifting problems, embracing ecosystem-based adaptation, seeking synergy between interventions, and incorporating adaptability into designs. The 3PSP approach emerges as a holistic framework that considers both risks and benefits, contributing valuable insights to the discourse on integrating urban and river basin water management, improving our ways of dealing with extreme weather events while maximizing the day-to-day benefits of our interventions.@en

Low Impact Development (LID) was promoted as an alternative to conventional urban drainage methods. The effects of LID at the site or urban scales have been widely evaluated. This project aims to investigate the impact of LID implementation on basin runoff at a regional scale in a half-urbanized catchment, particularly the overlap of urban and rural sub-flows at peak times. A SUPERFLEX conceptual model framework is adapted as a semi-distributed model to simulate the rainfall-runoff relationship in the catchment for San Antonio, Texas, as a case study. Scenario analyses of both urban development and LID implementation are conducted. Results show that (1) the infill urban development strategy benefits more from runoff control than the sprawl urban development; (2) in non-flood season, permeable pavements, bioretention cells, and vegetated swales decrease peak runoff significantly, and permeable pavements, bioretention cells, and green roofs are good at runoff volume retention; (3) contrary to the general opinion about the peak reduction effect of LID, for a partly urbanized, partly rural basin, the LID implementation delays urban peaks and may cause larger stacking of rural and urban peak runoffs, leading to larger basin peaks under extremely wet conditions.

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Urban surface waters are used in many different ways. With increasing demand for human use functions, improved insight is required into the functional quality of these waters. A method to assess this functional quality in a systematic way and for a wide variety of use functions is not available. We propose to use suitability indices (SIs) for assessing the suitability of urban water bodies for a variety of specific human uses. This study provides a new protocol for this, building on the water quality index and ecosystem services approaches in literature, by extending traditional water quality parameters with other characteristics of water bodies that determine suitability for a specific use function. By assessing suitability instead of traditional water quality, the functional quality of a water body for all kinds of uses can be determined in a consistent way. The protocol was demonstrated to be effective in developing SIs for three specific urban water use functions, namely: thermal energy extraction, transportation of goods and primary contact recreation. Application of the suitability indices in a case study in the city of Amsterdam, The Netherlands, resulted in spatially explicit information about suitability of surface waters for the three selected use functions. Sub-scores per parameter showed which characteristics of the urban water bodies should be changed to improve the suitability for these three functions. In this way, the SI approach for assessment of the functional quality of urban surface waters can be used to support function-oriented planning, design and maintenance of urban surface water systems.

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Due to the environmental crisis, there is a need for a more conscious and integrating design process within the field of urban infrastructure development. Through cooperation between civil engineering and spatial design resilience of the built environment can be increased. Delft University of Technology investigates interdisciplinary design as a method and incorporates this into its MSc-level education of students in the faculties of civil engineering and architecture. The focus of the research was on the reconstruction projects after disasters like hurricanes and tsunamis. By way of surveys of the participating students, the effectiveness of the interdisciplinary design methods used, and the interpretation of the terms multidisciplinary and interdisciplinary are revealed. From survey results about understanding of multidisciplinary and interdisciplinary it can be concluded that interdisciplinary design should entail a conscious and orchestrated process in which the disciplines present their ideas within a shared value system before systematic integration. The challenges are at personal and cognitive levels, an open attitude is necessary to be able to perceive and react, process and understand, retrieve information. Only then decisions on - and production of - appropriate responses come out of co-creation between engineering within the spatial design process.

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Due to climate change, droughts will intensify in large parts of the world. Drought and its impacts on nature and agriculture have been studied thoroughly, but its effects on the urban environment is rather unexplored. But also the built environment is susceptible to droughts and estimation of its vulnerability is the first step to its protection. This article is focusing on assessing the vulnerability of a city to groundwater drought, using parts of the lowland city of Leiden, the Netherlands, as a case study. Using a new urban drought categorization framework, groundwater drought is separated from soil moisture drought, open water drought and water supply drought, as each has its own impacts. Vulnerability was estimated as the aggregation of drought exposure and damage sensitivity. Drought deficit and duration were used as exposure indicators. Both a Fixed and Variable threshold method was used to quantify these indicators. To quantify drought vulnerability weights were assessed for selected exposure and damage sensitivity indicators using an Analytical Hierarchy Process (AHP) with a small number of experts. Based on these weights the spatial variation in vulnerability for groundwater drought follows damage sensitivity patterns—rather than exposure ones. And, out of all damage sensitivity indicators used, ‘land use', ‘low income' and ‘monuments’ contributed the most to the spatial variation in vulnerability. Due to the fact that the number of drought experts’ opinions in the AHP was limited these vulnerability results however remain uncertain. The proposed methodology however allows water managers to determine vulnerability of urbanized areas to groundwater drought, identify highly vulnerable areas and focus their mitigating actions.

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Canals and canalized rivers form a major part of surface water systems in European delta cities and societal ambitions to use these waters increase. This is the first assessment of how suitability of these waters can improve for three important uses: transportation, thermal energy extraction (TEE) and recreation. We assess suitability with Suitability Indices (SIs) and identify which alterations in the water system are needed to improve SI scores in Amsterdam, The Netherlands, and Ghent, Belgium. The results show spatial variability in suitability scores. Current suitability for transportation is low (SI score = 1) to excellent (SI score = 4), for TEE fair (SI score = 2) to excellent (SI score = 4), and suitability for recreation is low (SI score = 1). Suitability could improve by enlarging specific waterway dimensions, increasing discharge and clarity, and by enhancing microbiological water quality. The same methodology can be applied to optimize designs for new water bodies and for more water uses.

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Despite being widely implemented, sustainable urban drainage systems (SUDS) do not always function flawlessly. While SUDS have been tested extensively and seem to perform well on a laboratory or pilot scale, practitioners’ experience is different: failures in SUDS occur regularly in practice, resulting in malfunctioning systems, water nuisance and high costs. To anticipate their malfunctioning, and thus to improve their performance, a better understanding of failures occurring in SUDS and their underlying causes is needed. Based on an explorative case-study approach, consisting of site visits and semi-structured interviews with urban water professionals, this study presents an inventory of technical failures in SUDS and an analysis of their root causes. In total, 70 cases in 11 Dutch municipalities have been documented. The results show that the interfaces between SUDS and other urban systems are prominent failure locations. In addition, we found that failures originate from the entire development process of SUDS, i.e., from the design, construction and user/maintenance phase. With respect to the causes underlying these failures, our results show that these are mainly socio-institutional in nature. These are valuable insights for both practitioners and scholars, contributing to a renewed socio-technical urban water system with more sustainable water management practices.

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Integrating sustainable urban water management into the urban planning process is essential for developing water-resilient cities. To this end, the central government of the People’s Republic of China initiated the “Sponge City” programme. However, challenges and gaps exist in current urban planning practice. The operationalizable planning approach to realise the multiple objectives of Sponge City is missing in the existing guidelines. Using a local example of Sponge City planning in Nanjing City as a case study, this paper outlines the current Sponge City approach from the perspectives of planning content and planning process. A qualitative comparative analysis between Nanjing’s Sponge City planning and Auckland Water Sensitive Design, as well as an evaluation of the Sponge City approach through the lens of Dutch urban water management, identified key missing elements that would enhance the current Sponge City planning approach. Examples include targets for pluvial flood protection, a strategy for planning interventions, and tools for interdisciplinary cooperation in the planning process. This enhanced approach was successfully applied in the Sponge City planning for Qinhuai District, Nanjing City. Nevertheless, challenges on data availability and the decision-makers’ mindsets called for more efforts on the interface of research and policy development for upscaling the Sponge City approach.@en

The ambition to Build Back Better after a serious flood disaster is a complex challenge. A comprehensive, multi-disciplinary redevelopment planning process is required to reduce the flood risk and meanwhile create sustainable solutions that bring added value to society every day. General planning principles can be formulated on how to develop the physical conditions for flood resilience, while building a better place to live and work. Scoping and the charrette method are to be applied for pairing and integrating disciplinary results, to co-create Better plans in an interdisciplinary planning process. Two disaster recovery cases in Japan, after the 2011 Tohoku tsunami, and one case on Grand Bahama, after 2019 hurricane Dorian, were studied by multidisciplinary teams of students and staff to investigate in how far Building Back Better was, or is to be, realized. This was done by confronting the practice of the reconstruction process and the resulting plans with the guiding principles for the physical concepts and interdisciplinary planning approach. Practice shows that Building Back Better is suffering from a lack of integration of disciplinary solutions, guided by existing planning regulations and practices and driven by the need for flood safety and by the urgency of the reconstruction works. @en

Scientific literature currently lacks comprehensive understanding of urban surface water use functions. This hampers sound analysis of the demand and potential supply of these functions. This study provides a comprehensive overview of potential use functions, by integrating knowledge from ecosystem services and integrated urban water management fields. Analysis of water-related management plans for Toronto and Amsterdam shows that surface water is currently being used for a variety of functions related to nutrition, energy, water regulation, recreation, symbolic use, transportation and floating buildings. Notably, many use functions involve in situ use, rather than water extractions. Interviewed water managers and spatial planners in both cities expect demand of most use functions to increase by 2040, especially demand for thermal energy extraction, recreation and transportation. Some identified novel demands, such as climate regulation and reuse of waste products from waterway maintenance. Increasing demand is mainly driven by urban growth, climate change and sustainability ambitions. This study found urban surface water uses that are usually not acknowledged in scientific literature on urban water management. This comprehensive overview supports planning, design, and maintenance of urban surface waters, laying the foundation for future research on supply and demand of urban water use functions.

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Planning Support Systems (PSS) are increasingly used to support collaborative planning workshops in urban adaptation practice. Research has focused on developing such tools and evaluating their use in workshops but has not measured tools' effects over time on real planning processes, on the participants involved, and on the final outcomes. The role that tools play in adaptation planning, therefore, remains unclear. A longitudinal case study was made to evaluate a PSS, the Adaptation Support Tool (AST), in a design workshop for sustainable urban water management, in Berlin, Germany. The case study also served to test the evaluation framework and generate insights regarding systematic evaluations of tools in planning processes. The case study was carried out over eighteen months, to capture both the details of the workshop and its longer-term effects on the project and participants. Our results show that the AST's most evident effects were (1) contributory and less tangible in nature (e.g., supporting learning), than directly causal and concrete (e.g., affecting planning decisions), and (2) a function of the process and context in which the workshop took place. This study demonstrates that making systematic, longitudinal evaluations are valuable for studying the role of PSS in urban adaptation planning.

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One of the processes by which open water cools the air during hot summer days is by storing the heat and increasing its own temperature. This heat is then released at night. The aim of this paper is to analyze this cooling process by quantifying the magnitude of turbulent, latent and sensible, heat fluxes in comparison to radiative and ground fluxes. A detailed vertical temperature profile was measured in an urban pond (~70 cm deep with surface area of 3,627 m²) in Delft (NL) using Distributed Temperature Sensing for a period of one month. The results show that, from the total of 2.7 MJm⁻² of heat released by the pond on an average summer night, 43% of the thermal energy is emitted as longwave radiation, 39% as latent energy, and only 11% as sensible heat. An additional 0.10–0.32 MJm⁻² is transferred into the bottom of the lake. Temperature distribution and cooling of the water profile is influenced by weather conditions during the preceding day. This paper provides an insight into a behavioral pattern of an urban pond at night. The results can shed some light into the potential of urban bodies to increase the air temperature of their surroundings at night.

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Planning Support Systems (PSS) are a promising tool for involving stakeholders in urban adaptation workshops. Past research has focused on the use and added value of PSS. While earlier studies have widely acknowledged the importance of context in determining the effectiveness of PSS, there has so far been no dedicated study of the influence of context on the use and added value of these tools in real planning workshops. To address this gap, we made an in-depth exploratory case study of a PSS, called the Adaptation Support Tool (AST), used in an adaptation planning workshop in Guayaquil, Ecuador. The workshop used the AST to support collaborative spatial planning for urban water management, at the neighbourhood scale. Interviews, questionnaires, observations and document review were used to investigate the influence of three contextual factors on the use and added value of the AST. The studied contextual factors are: 1) the style of tool use, 2) the phase of planning, and 3) the local project setting. Our findings indicate that the style of tool use and the local project setting were the most important contextual factors in determining the use and added value of the AST during the workshop. Meanwhile, the phase of planning appears to be critical for achieving impacts at the project level. This exploratory case study is a modest first contribution to understanding the influence of context on the use and added value of PSS in practice. Nevertheless, the findings indicate that further exploration of this topic could offer important insights to PSS use in practice. The influence of context on the use and added value of Planning Support Systems in workshops: an exploratory case study of climate adaptation planning in Guayaquil, Ecuador.@en

The urban heat island effect was first described 200 years ago, but the development of ways to mitigate heat in urban areas reaches much further into the past. Uchimizu is a 17th century Japanese tradition, in which water is sprinkled around houses to cool the ground surface and air by evaporation. Unfortunately, the number of published studies that have quantified the cooling effects of uchimizu are limited and only use surface temperature or air temperature at a single height as a measure of the cooling effect. In this research, a dense three-dimensional Distributed Temperature Sensing (DTS) setup was used to measure air temperature with high spatial and temporal resolution within one cubic meter of air above an urban surface. Six experiments were performed to systematically study the effects of (1) the amount of applied water; (2) the initial surface temperature; and (3) shading on the cooling effect of uchimizu. The measurements showed a decrease in air temperature of up to 1.5 ◦C at a height of 2 m, and up to 6 ◦C for near-ground temperature. The strongest cooling was measured in the shade experiment. For water applied in quantities of 1 mm and 2 mm, there was no clear difference in cooling effect, but after application of a large amount of water (>5 mm), the strong near-ground cooling effect was approximately twice as high as when only 1 mm of water was applied. The dense measurement grid used in this research also enabled us to detect the rising turbulent eddies created by the heated surface.@en

A phenomenon known as the skin effect-a layer of surface water that is colder than the water beneath it-was previously described in oceanography and verified in lab measurements. Only a few measurements have been done on the skin effect in field conditions, and therefore this phenomenon is relatively unknown. This paper presents measurements of the skin effect for three fresh water bodies in the Netherlands, Israel and Ghana. Using Distributed Temperature Sensing, high temporal and spatial resolution measurements were made below, at and above the air-water surface. Measurements presented in this study suggest that the skin effect of fresh water bodies is predominantly a daytime phenomenon and only occurs during low to zero wind speeds. The thickness of the skin effect was measured to be an order of magnitude larger than the previously assumed less than 1 mm.

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In the face of a changing climate, many cities are engaged in adaptation planning and are using participatory workshops to involve stakeholders in these initiatives. Different tools are being used to structure the process and content of participatory planning workshops, but it is unclear what effect the tools have on the workshops and their results. We evaluated three different tools (Group Model Building, the Adaptation Support Tool, and the Stress Test Guideline) and a tool-free approach in repeated simulated workshops, to observe and compare (1) the way workshops played out, and (2) the direct outcomes that were achieved. Tools appear to influence both aspects. Specifically, we measured differences in the learning effects in groups, in the development of shared understanding within groups, in the types of plans that are developed by groups, and in the nature of participation during the workshops. Further research is needed to translate these results into practice, but this is a first step in advancing knowledge about the influence of tools in participatory planning activities.

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Rapid urbanization and an increasing number and duration of heat waves poses a need to mitigate extremely high temperatures. One of the repeatedly suggested measures to moderate the so called urban heat island are green roofs. This study investigates several extensive sedum-covered green roofs in Utrecht (NL) and their effect on air temperature right above the roof surface. The air temperature was measured 15 and 30 cm above the roof surface and also in the substrate. We showed that under well-watered conditions, the air above the green roof, compared to the white gravel roof, was colder at night and warmer during the day. This suggests that extensive sedum-covered green roofs might help decrease air temperatures at night, when the urban heat island is strongest, but possibly contribute to high daytime temperatures. The average 24 h effect of sedum-covered green roof was a 0.2 °C increase of air temperature 15 cm above the ground. During a dry year the examined green roof exhibited behavior similar to conventional white gravel roof even exhibited slight cooling effect in late afternoon. Interestingly, the pattern of soil temperature remained almost the same for both dry and well-prospering green roofs, colder during the day and warmer at night.

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The Urban Heat Island (UHI) was first described 200 years ago, but ways to mitigate heat in urban areas reach much further into the past. Uchimizu is a 17th century Japanese tradition, in which water is sprinkled around houses, temples, and in gardens to cool the ground surface and the air, and to settle the dust. Nowadays, megacities such as Tokyo are aiming to revive the - by modern technology suppressed - method, and uchimizu is promoted by local authorities as a "clever way to feel cool". Unfortunately, the number of published studies that have quantified the cooling effects of uchimizu is limited, and only uses measurements of the surface temperature, or air temperature at a single height, as a measure of the cooling effect. In this research a dense 3D Distributed Temperature Sensing (DTS) setup was used to measure air temperature within once cubic meter of air above an urban surface with high spatial and temporal resolution. Six experiments were performed to systematically study the effect of (1) applied water amount, (2) initial surface temperature, and (3) shading on the cooling effect of uchimizu. We present the results and the subsequent analyses of these experiments, done during summer in Delft, The Netherlands. We show that this simple water sprinkling method has the potential to decrease extreme temperatures in impervious and paved parts of urban areas considerably. Besides mitigating the UHI, uchimizu practice is also an opportunity to increase awareness among citizens, and stimulate citizen participation in solving heat stress problems and energy saving. By providing refreshing insights on the cooling effect of uchimizu, we aim to contribute to the modern revival of this old tradition.@en