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Current adaptation responses to sea-level rise tend to ignore the interplay of adaptation responses and city development, leading to unintended consequences with adverse impacts on citizens’ welfare, institutional performance, and economic capacities. This study introduces a generic causal loop diagram (CLD) model, a novel approach exploring the dynamics of coastal adaptation and city development at a city scale. Unveiling key feedback mechanisms—flood risk perception, economic capacity, and trust—reveals their central role in driving negative repercussions, irrespective of the chosen strategy (protection, accommodation, planned relocation). Specifically, fiscal motivations to increase flood exposure and reinforcing dynamics between trust and institutional capacity can significantly impact socioeconomic vulnerabilities. Protection and accommodation may stimulate development in risk areas, while planned relocation faces challenges. However, well-planned relocation offer resource-effective adaptation, mitigating economic and political repercussions through long-term planning. Although the CLD lacks consideration for external drivers and spatial-temporal complexities, it provides crucial insights for coastal adaptation planning. Emphasizing holistic decision-making and multidimensional effects, this research supports informed policy formulation, fostering collaboration between urban planners and flood risk managers for robust and sustainable coastal adaptation pathways.

Baggrund. Udfordringer vedrørende oversvømmelser fra havet har fået øget opmærksomhed i de senere år. De danske kommuner har fået større myndighedsansvar vedrørende kystbeskyttelse og samtidig er havniveaustigninger og stormflod blevet et opmærksomhedspunkt i klimatilpasningen. Formål. Formålet med denne undersøgelse er at belyse, hvorledes udvalgte danske kommuner aktuelt (2020-2022) arbejder med tilpasning til oversvømmelser fra havet og det stigende havvand. Metode. Undersøgelsen er gennemført dels gennem samtaler med repræsentanter fra samtlige 19 kystkommuner involveret i de 18 pilotprojekter, der i årene 2019-2022 har fået støtte fra Realdania til at gennemføre en modningsproces om byudvikling og havvandsstigninger, dels ved fysiske besøg og ’walk-and-talks’ i de konkrete projektområder. Disse samtaler fandt sted i perioden fra september 2020 til september 2022. På grund af COVID-19 har det ikke været muligt at gennemføre feltbesøg i tre af de 18 pilotprojekter; her foregik interviewene online. Resultater. I udgangspunktet har pilotkommunerne et stærkt fokus på stormflod som den primære udfordring, mens tilpasning til det stigende havvand er mere sekundært. Samtidig er der en prioritering af beskyttelse som den dominerende løsningsramme, frem for imødekommelse (at leve med vandet), tilbageføring (udfasning af bebyggelse) og friholdelse (undgå nybyggeri i oversvømmelsesudsatte områder). Tretten ud af 18 kommuner står aktuelt i en situation, hvor der skal tages stilling til, hvordan - eller om - der skal byudvikles i lavtliggende kystnære områder, som f.eks. tidligere erhvervshavne. Der sker en modningsproces i kommunerne, hvilket betyder at forståelses- og løsningsrammen bliver nuanceret over tid og der er en bevægelse fra ’teknologidiskussioner’ frem mod mere helhedsorienteret kystudvikling med et mere processuelt fokus. Aktuelt slutter planlægningshorisonten i år 2100, mens en mere grundlæggende diskussio

I perioden 2018-2022 har Realdania og Kystdirektoratet indgået partnerskab om projektet Byerne og det stigende havvand. I alt 19 kommuner har modtaget støtte fra partnerskabet til udvikling af pilotprojekter, der relaterer sig til kystbyers tilpasning til oversvømmelser fra havet. Pilotprojekterne ligger i såvel store kommuner og byer som København, Aalborg og Randers, mellemstore byer som Svendborg, Skive og Nykøbing Falster, samt mindre byer som Taarbæk, Strøby Egede og Juelsminde. Sideløbende er der kørt et netværks- og forskningsspor, som haft til formål at bygge bro mellem forskning og praksis, og som samtidig har bidraget til, at forskerne har kunne høste erfaringer på tværs af kommunerne fra deres arbejde med kystbyer og klimaforandringer. Det er der kommet en tværgående opsamlingsrapport ud af. Rapporten ’Man vil jo gerne en by – indsigter fra 19 pilotkommuners arbejde med udvikling af kystbyer i lyset af det stigende havvand’ formidler de tværgående emner, der fylder i de kommunale forvaltninger, når det gælder tilpasning til oversvømmelser fra havet. Der er fire hovedkonklusioner i rapporten. For det første, at der i kommunerne er fokus på beskyttelse, hvilket sker på bekostning af imødekommelse og især tilbageføring og friholdelse af bebyggelse som løsningsmuligheder i forhold til oversvømmelser fra havet. For det andet er der fokus på stormflod, mens de meget langsigtede, permanente og løbende stigninger i havniveauet ikke for alvor tages med i overvejelserne om byens udvikling og tilpasning til klimaforandringerne. For det tredje er der i de fleste kommuner konsensus om, at de lavtliggende kystområder, herunder særligt havneområderne, er vigtige byudviklingsarealer. Og endelig for det fjerde, viser undersøgelsen, at de danske kommuner er meget forskellige steder rent modningsmæssigt i deres arbejde med udvikling af kystbyer i lyset af det stigende havvand. Konsekvenserne af dette er, at det er svært fo

En tværfaglig forskergruppe har interviewet 19 kommuner om arbejdet med byudvikling i lyset af det stigende havvand. I denne artikel opsummeres undersøgelsen, der bl.a. konkluderer, at der er brug for mere diskussion af byudvikling i oversvømmelsestruede områder. Og så opfordrer forskerne til kompetenceopbygning i forhold til arbejdet med det stigende havvand og til at tænke i dynamisk foranderlig byudvikling.

Connectivity among blue-green infrastructure (BGI) is a vital condition for enhanced ecosystem services provision in metropolitan regions where the social-ecological systems are interwoven. In this study, we conduct a comparative spatial assessment of transversal connectivity of natural surfaces to freshwater sources for the metropolitan areas of Berlin, London, and Paris. We focus on the transversal connectivity, which describes the lateral connection between natural surfaces and water surfaces, as opposed to connections along a water surface geometry. Initially, we compare the distribution ratios of water surfaces, natural lands, and transportation network at both the metropolitan and the urban level, relying on the Urban Atlas (UA) land-use and land-cover data. Our results show that at metropolitan level, Berlin has higher shares of water and natural surfaces (2.6 % and 40.1%) compared to London (1.32 % and 13.4 %) and Paris (0.9 % and 23.1 %). On the contrary, the transportation network covers less surfaces in Berlin (2.00 %) than in London (4.71 %) and Paris (3.62 %). Second, we investigate the connectivity among BGI elements, and most importantly, to the water surfaces. We considered the water surfaces as pivot elements in the landscape, while investigating the connectivity of natural areas to them. As part of the methodology, the transportation network is introduced in the analysis as the main fragmenting geometry. Our results show that in all three cases, more than 80 % of natural surfaces patches had no connection to freshwaters. Among them, the natural surface patches of Berlin record the highest level of transversal connectivity to freshwaters (17 %) On the other hand, London leads the ranking on the water surfaces that are not connected to any natural surface (>60 %). Transversal connectivity can be greatly increased with minor adjustments in spatial planning. For example, in Berlin the percentage of natural surfaces connected to freshwater jumps from

Samlet viden og dialog: Ingen kan vide alt, og i tilpasningen af vores kystbyer er der brug for at udveksle viden, samarbejde og gå i dialog. Den Lille Blå Parlør om Havstigning er et bidrag til dialogen om klimatilpasning og løsningsrum i fremtidens by- og landskabsudvikling. Parløren søger at gå på tværs af viden, fagligheder, interesser, aldersgrupper, ansvarsområder og visioner for på den vis at bidrage til at binde samtalen mellem forskellige interessenter sammen. Baggrund, formål og struktur: Parløren er struktureret som en ABC med en række nøgleord på tværs af tematiske sammenhænge. Her beskrives termer og begreber alfabetisk og flere steder fulgt af illustrationer. Nogle steder udbygges teksten med en note, hvor primære kilder angives eller der gives link til yderligere viden. Mange af termerne knytter sig nært til, eller overlapper med, andre ord og begreber. Tingene hænger sammen, og jo mere helhedsorienteret der arbejdes med klimatilpasning, des mere hænger forskellige begreber og tilgange sammen. Af samme årsag er parløren - ligesom andre parlører – ikke tiltænkt kronologisk læsning men kan ses som et lille opslagsværk med en række kernebegreber, hvorefter yderligere viden kan søges. Målgruppe og hvordan bogen kan bruges: Den Lille Blå Parlør er udarbejdet som formidling til en bred gruppe af både lægfolk og fagfolk, elever og studerende, borgere og politikere, praktikere og forskere. Det er en introduktion til en række kernebegreber og termer, der ofte er vigtige i forbindelse med udvikling af løsninger for havstigning og kraftigere stormfloder i de danske kystbyer. Formålet er at give en overordnet, introducerende viden, som den enkelte kan bruge som enkeltopslag, eksempelvis Bidragsmodel, Kote eller Omkostningseffektivitet, eller som tematiske opslag som f.eks. Løsningstypologier, der spænder bredt med korte beskrivelser af forskellige tilgange. Parløren kan også ses som en overordnet bred introduktion, hvorefter man selv k

Current adaptation responses to sea-level rise tend to focus on protecting existing infrastructure resulting in unsustainable adaptation pathways. At the same time, urban development compromises a city’s adaptive capacity if the climate risk component is ignored. While fighting for the same space, these two domains are currently widely analyzed separately. This paper develops a framework for integrating sustainability assessments of sustainable urban development (SUD) and coastal adaptation to climate change (CACC). Through a systematic literature review, we collected more than 2,700 indicators for SUD and 1,800 indicators for CACC. The indicators occurring most frequently are extracted and structured into frameworks. The study highlights the differences and similarities between the two frameworks. We further identify complementary and conflicting objectives that can advance or inhibit the effective integration of SUD and CACC. CACC tends to focus on assessing specific adaptation measures and their immediate impact on the city’s vulnerability, ignoring wider impacts on socioeconomic systems. SUD considers the city and its functions as a whole but ignores vulnerability assessments across urban subsystems. We develop a combined framework for sustainability assessment that may serve as a basis for both qualitative and quantitative integrated studies under the paradigm of sustainable adaptation.

When assessing strategies for implementing Nature-Based Solutions (NBS), it is paramount to identify and quantify all benefits for securing better, informed decisionmaking. Nevertheless, there appears to be a lack of primary data for linking the valuation of NBS sites with the preferences and attitudes of people interacting with them and their connection to supporting efforts to reduce biodiversity loss. This is a critical gap, as the socio-cultural context of NBS has been proven to play a big role in NBS valuation, especially for their non-tangible benefits (e.g. physical and psychological well-being, habitat enhancements, etc.). Consequently, through cocreation with the local government, we co-designed a contingent valuation (CV) survey to explore how the valuation of NBS sites may be shaped by their relationship with the users and the specific respondent and site characteristics. We applied this method to a case study of two distinct areas located in Aarhus, Denmark, with notable differences related to their attributes (e.g. size, location, time passed since construction). The esults obtained from 607 households in Aarhus Municipality show that the personal preferences of the respondent are the most relevant driver of value, surpassing both the perceptions linked to the physical features of the NBS and the socio-economic characteristics of the respondents. Specifically, the respondents attributing most importance to nature benefits were the ones assigning a higher value to the NBS and being willing to pay more for an improvement of the nature quality in the area. These findings highlight the relevance of applying a method assessing the interconnections between human perceptions and nature benefits to ensure a holistic valuation and purposeful design of NBS.

Erfaringer fra 8 kommuner, der har fået Realdania-midler til kystbeskyttelsesprojekter, peger på behov for at anvende længere tidshorisonter og en systematisk videndeling.

Mapping and prediction of inundated areas are increasingly important for climate change adaptation and emergency preparedness. Flood forecasting tools and flood risk models have to be compared to observe flooding patterns for training, calibration, validation, and benchmarking. At the regional to continental scales, satellite earth observation (EO) is the established method for surface water extent (SWE) mapping, and several operational global-scale data products are available. However, the spatial resolution of satellite-derived SWE maps remains a limiting factor, especially in low-lying areas with complex hydrography, such as Denmark. We collected thermal imagery using an unmanned airborne system (UAS) for three areas in Denmark shortly after major flooding events. We combined the thermal imagery with an airborne lidar-derived high-resolution digital surface model of the country to retrieve high-resolution (40 cm) SWE maps. The resulting SWE maps were compared with low-resolution SWE maps derived from satellite earth observation and with potential flooded areas derived from the high-resolution digital elevation model. We conclude that UASs have significant potential for SWE mapping at intermediate scales (up to a few square kilometers), can bridge the scale gap between ground observations and satellite EO, and can be used to benchmark and validate SWE mapping products derived from satellite EO as well as models predicting inundation.

We propose and demonstrate a new approach for fast and accurate surrogate modelling of urban drainage system hydraulics based on physics-guided machine learning. The surrogates are trained against a limited set of simulation results from a hydrodynamic (HiFi) model. Our approach reduces simulation times by one to two orders of magnitude compared to a HiFi model. It is thus slower than e.g. conceptual hydrological models, but it enables simulations of water levels, flows and surcharges in all nodes and links of a drainage network and thus largely preserves the level of detail provided by HiFi models. Comparing time series simulated by the surrogate and the HiFi model, R2 values in the order of 0.9 are achieved. Surrogate training times are currently in the order of one hour. However, they can likely be reduced through the application of transfer learning and graph neural networks. Our surrogate approach will be useful for interactive workshops in initial design phases of urban drainage systems, as well as for real time applications. In addition, our model formulation is generic and future research should investigate its application for simulating other water systems.

Nature-Based Solutions (NBS) can be defined as solutions based on natural processes that meet societal challenges and simultaneously provide human well-being and biodiversity benefits. These solutions are envisioned to contribute to operationalizing sustainable development strategies, especially in the context of adaptation to climate change (e.g. flood risk reduction). In order to quantify NBS performance, ease their uptake and advocate for them as alternatives to “business-as-usual” infrastructures, a comprehensive, holistic valuation of their multiple benefits (multiple advantages and disadvantages) is needed. This entails quantifying non-market benefits for people and nature in addition to determining the (direct) cost-benefit of the risk-reduction measure. Despite the importance given to the assessment of non-tangible benefits for people and nature in the literature, systematic data collection on these dimensions seems to be missing. This study reviews publications that used stated preference methods to assess non-market human benefits of NBS and NBS-like strategies. Its aim is to highlight any biases or knowledge gaps in this kind of evaluation. Our results show that the valuation of non-tangible benefits of NBS (e.g. increased recreation and well-being, enhanced biodiversity) still suffers from a lack of common framing. Despite some steps being taken on enabling interconnected benefit assessments, unexploited opportunities concerning the integrated assessment of non-market human and nature benefits predominate. Moreover, the research to-date appears based on a case-to-case approach, and thus a shared holistic method does not emerge from the present literature, potentially delaying the uptake of NBS. We argue that future research could minimize missed opportunities by focusing on and systematically applying holistic benefits assessments. Methods based on stated preference surveys may help to ensure holistic approaches are taken, as well as contributing to thei

Nature-based solutions may actively reduce hydro-meteorological risks in urban areas as a part of climate change adaptation. However, the main reason for the increasing uptake of this type of solution is their many benefits for the local inhabitants, including recreational value. Previous studies on recreational value focus on studies of existing nature sites that are often much larger than what is considered as new NBS for flood adaptation studies in urban areas. We thus prioritized studies with smaller areas and nature types suitable for urban flood adaptation and divided them into four common nature types for urban flood adaptation: sustainable urban drainage systems, city parks, nature areas and rivers. We identified 23 primary valuation studies, including both stated and revealed preference studies, and derived two value transfer functions based on meta-regression analysis on existing areas. We investigated trends between values and variables and found that for the purpose of planning of new NBS the size of NBS and population density were determining factors of recreational value. For existing NBS the maximum travelling distance may be included as well. We find that existing state-of-the-art studies overestimate the recreational with more than a factor of 4 for NBS sizes below 5 ha. Our results are valid in a European context for nature-based solutions below 250 ha and can be applied across different NBS types and sizes.

When assessing strategies for implementation of Nature-Based Solutions (NBS) it is fundamental to quantify all benefits for securing better, informed decision making. Particularly relevant is the quantification of their multiple co-benefits for communities and the environment. One of the most widespread techniques to quantify these values is to use contingent valuation (CV) methods, such as the Willingness-To-Pay (WTP) approach. Within the CV method, questionnaires are the main tool used to elicit the value attributed to a specific good by the respondents. However, many studies focus on site-specific economic valuation, whereby transferability to other locations is jeopardized. We therefore created a survey to explore how the valuation of an NBS is shaped by its relationship with the users (e.g. frequency and length of visits), and how these responses are linked to both the respondents and the sites’ characteristics (e.g. socio-economic status, size of the NBS, etc.). We applied this method to a case study comprised of two distinct areas located in Aarhus, Denmark, asking users to explore their perception of the two NBS sites with different features. Both NBS sites have as overarching goals to (i) prevent flooding from cloudburst or water bodies, (ii) improve the biodiversity in the area, and (iii) benefit the local population, e.g. by providing more recreational areas. Despite these common goals, the two sites differ by a number of characteristics, i.e. size, location, and time passed since construction. One NBS involves a large artificial lake in a peri-urban setting, while the other is a small urban park. Respondents were allowed the option of either expressing a value for only one, or for both of the sites. We analyzed both responses that stated a WTP and protest votes, that is, responses that rejected the valuation scenario altogether. We found that older citizens are more likely to protest, as well as those not visiting the sites. For the r

Climate change will cause more extreme events to happen in the future, along with which is the higher frequency of rain. Besides, the growth of population and urbanization also results in more burden to the urban drainage systems. In order to understand the response of a drainage system, physically-based distributed models (PDM) such as Mike Urban+ are often used. However, these models require intensive computational power, which makes them not feasible for scenario analyses or real-time control. Conceptual models are preferred since they can produce fast simulation results. Nevertheless, conceptual models’ parameters are concepts that cannot be directly derived from reality, but through calibration or establishment of empirical links with the physical systems. This study proposes a method to derive parameters of the conceptual models based on the drainage systems’ own physical characteristics using the storage-outflow (SQ) relationship. Two conceptual models are built in Python script. The first one optimizes and computes the SQ relationship for transport stretches of various lengths and slopes. The second model uses the obtained SQ relationship to simulate two virtual cities’ discharges, each city is divided into 4 different levels of lumping. The conceptual model for transport stretch performs accurately with low errors. However, discharge hysteresis in long and flat pipes cannot be captured precisely. In comparison to using Mike Urban+, the conceptual models for simulating city discharges are up to 70 times faster with very high accuracy. The NSEs of different lumping levels are around 0.94 while the peak errors both in magnitude and time are small. It is recommended that the cities should be divided into compartments with the areas of around 7−15 ha for high quality results and low computational time. The quality of conceptual models does not depend on the shape of the city. Results show that the conceptual models in this study are capable of simulating outflow

Due to climate change and urbanization, urban flood modelling has become an increasingly important tool in assessing flooding and associated damage costs. However, large computational demands of state-of-the art hydrodynamic flood models makes multiple and real-time simulations unfeasible. This study presents a fast-dynamic GIS-based flood model, FloodStroem. FloodStroem generates a surface network of depressions (bluespots) and flow paths, and routes surcharged water from a subsurface drainage model through the network resulting in flood depth maps and associated damage costs. FloodStroem is tested on three sub-catchments in Elster Creek Catchment, Melbourne, Australia and benchmarked against the 2D distributed hydrodynamic model MIKE 21 and two other simplified models, RUFIDAM and CA-ffé. FloodStroem is robust to the number of bluespots included. For the three sub-catchments, FloodStroem can reproduce flooding time, pattern, depth, and damage costs sufficiently, but has a tendency to underestimate flooding upstream and overestimate flooding downstream. Performance is best for the large, steep sub-catchments and largest rainstorms, where FloodStroem performs better than the two other simplified models. The Critical Success Index (CSI) ranges from 23 % for a 5-year storm event in a flat catchment to 65 % for a 100-year return period for a steeper catchment. With respect to simulation time, FloodStroem is five orders of magnitude faster than the 2D hydrodynamic model, and 33 times faster when including the entire model setup time, which has potential for further reduction by optimization of the workflow.

Due to climate change and urbanization, urban flood modelling has become an increasingly important tool in assessing flooding and associated damage costs. However, large computational demands of state-of-the art hydrodynamic flood models makes multiple and real-time simulations unfeasible. This study presents a fast-dynamic GIS-based flood model, FloodStroem. FloodStroem generates a surface network of depressions (bluespots) and flow paths, and routes surcharged water from a subsurface drainage model through the network resulting in flood depth maps and associated damage costs. FloodStroem is tested on three sub-catchments in Elster Creek Catchment, Melbourne, Australia and benchmarked against the 2D distributed hydrodynamic model MIKE 21 and two other simplified models, RUFIDAM and CA-ffé. FloodStroem is robust to the number of bluespots included. For the three sub-catchments, FloodStroem can reproduce flooding time, pattern, depth, and damage costs sufficiently, but has a tendency to underestimate flooding upstream and overestimate flooding downstream. Performance is best for the large, steep sub-catchments and largest rainstorms, where FloodStroem performs better than the two other simplified models. The Critical Success Index (CSI) ranges from 23% for a 5-year storm event in a flat catchment to 65% for a 100-year return period for a steeper catchment. With respect to simulation time, FloodStroem is five orders of magnitude faster than the 2D hydrodynamic model, and 33 times faster when including the entire model setup time, which has potential for further reduction by optimization of the workflow.

In this work, an unsupervised model selection procedure for identifying data-driven forecast models for urban drainage systems is proposed and evaluated. Specifically, we consider the case of predicting inflows to wastewater treatment plants for activating wet weather operation (aeration tank settling, ATS) using Box–Jenkins models. The model selection procedure considers different model structures and different objective functions. The hyperparameter search space is constrained based on the time of concentration in the catchment. Objective function criteria that minimize one-step-ahead as well as multi-step prediction errors are considered. Finally, we consider two criteria for unsupervised selection of the best-performing model. These measure the agreement of observed and predicted hydrographs (persistence index), as well as the binary exceedance of critical flow thresholds (critical success index (CSI)). Our work shows that forecast models can be developed in an unsupervised manner, and ATS activation is correctly forecasted in 60–90% of the events. The selected model structures reflect the physical behaviour of the catchment. Models should not be selected on operational criteria like the CSI due to a risk of overfitting. The degree to which rainfall input improves forecasts depends on the specific catchment, and the objective function criterion that should be used for coefficient estimation depends on the application context.