Search Results (87)

The continuous increase in Renewable Energy Sources (RES) in Greece’s electricity system has led to growing energy curtailment due to limited grid capacity, especially in high-production regions. According to recent data, more than 200 GWh of clean energy was curtailed in a single quarter in 2024, highlighting the urgent need for effective storage solutions. Curtailment represents a growing system level challenge, but it also creates an opportunity to convert surplus renewable electricity into green hydrogen through electrolysis. This study quantifies the hydrogen production potential of curtailed RES electricity in four Greek regions, Peloponnese, Crete, Thrace, and Western Macedonia, and evaluates alternative storage pathways under harmonized techno-economic assumptions. A scenario-based framework is developed using regional RES capacity, curtailment estimates, electrolyzer efficiency, hydrogen conversion factors, and indicative storage cost ranges. The analysis compares pressurized tank storage, underground storage, and hybrid configurations, while also estimating avoided CO₂ emissions from the substitution of grey hydrogen. The results indicate substantial regional variation. The Peloponnese exhibits the highest annual hydrogen potential, followed by Crete, Thrace, and Western Macedonia, while each region presents different infrastructure constraints and deployment roles. Mainland regions with access to geological storage show lower indicative hydrogen costs than island systems, where storage and export constraints increase costs. The findings show that curtailed renewable electricity can function as a low-carbon feedstock for hydrogen production in Greece, supporting grid flexibility, regional decarbonization, and the gradual development of hydrogen hubs under differentiated regional strategies. Full article

This study proposes a comprehensive methodology for the design and performance assessment of infiltration ponds integrated within hybrid grey–green urban drainage systems. The scope of the ponds is twofold: (i) increase infiltration of rainwater, and hence groundwater recharge, and (ii) decrease pluvial discharge downstream. The framework is applied to the Rome Technopole district, which serves as a pilot case for testing and demonstrating the procedure. Through 30-year continuous simulations performed with the EPA Storm Water Management Model and forced with a 5 min historical rainfall, the approach enables a performance-based evaluation that captures the full hydrological variability and the hydraulic performances of urban drainage systems. The methodology relies on physically based models for both the grey stormwater drainage network and the infiltration ponds, combined with a long-term simulation and functional analysis under transient conditions. The approach explicitly represents the main hydrological processes, including runoff generation, flow routing, storage dynamics, infiltration, and soil moisture variability, enabling a quantitative evaluation of peak-flow attenuation, infiltration efficiency, groundwater recharge volumes, seasonal variability, and wet–dry cycle behaviour. The latter is used to assess the long-term evolution of pond performance and its implications for maintenance activities, including clogging development and removal. Scenario analyses explore the influence of pond geometry and storage volumes, highlighting the trade-offs between hydrological efficiency, evaporation losses, and drawdown times. Beyond the specific application to the Rome Technopole developed in this study, we propose a generalizable, practitioner-oriented design procedure suited to contexts where infiltration-based solutions are desirable but regulatory guidance is fragmented. The proposed design workflow identifies critical parameters for both the hydraulic design and the operational management of infiltration ponds, enabling a statistical evaluation of their performance. The analysis of peak-flow reduction, infiltrated volumes, and the timing and frequency of wet–dry cycles provides a robust technical basis for the proper sizing, integration, and long-term assessment of infiltration ponds within urban drainage planning. Full article

High-density urban areas face a critical trade-off between limited land resources and intensifying flood risks. This study develops a grey-green infrastructure (GGI) optimization framework that integrates hazard–exposure–vulnerability (H-E-V) risk assessment, surrogate modelling, and NSGA-III to simultaneously minimize cost, maximize flood control, and enhance water environmental benefits. The Suqian City case study reveals: (1) Grey-green coupling significantly outperforms single green infrastructure (GI), providing an additional 7.07–23.34 percentage points in flood risk control rate (FRCR). While GI reaches a performance bottleneck at 78.59% FRCR under extreme events, the GGI configuration maintains a high efficiency of >92.74%. (2) Risk-informed spatial targeting effectively reclassifies urban vulnerability. Under a 20-year return period, high-risk and medium-high risk areas are reduced by 80.99% and 52.15%, respectively. The validated surrogate models ensure high optimization efficiency with $R^2$ values exceeding 0.85. This framework provides a methodologically transferable decision-support tool for sponge city construction, demonstrating that strategic spatial allocation is as vital as infrastructure capacity for urban flood risk management. Full article

Hydrogen is increasingly recognized as a key vector for sustainable energy transitions, deep decarbonization, and enhanced energy security. This review evaluates major hydrogen types, grey, blue, and green, through a comparative assessment of production pathways, cost structures, technological maturity, and market readiness, with a focus on Sub-Saharan Africa (SSA). Grey hydrogen, while currently dominant due to established fossil-based infrastructure and low costs, is associated with high carbon emissions and climate-related risks. Blue hydrogen offers a transitional pathway via carbon capture and storage but faces constraints in SSA from high capital requirements, limited CCS infrastructure, and methane leakage. Green hydrogen, produced through renewable-powered electrolysis, represents the most sustainable long-term option, aligned with global net-zero goals and SSA’s abundant solar and wind resources, despite higher upfront costs. Synthesizing recent techno-economic, policy, and regional studies, the review highlights that prioritizing green hydrogen deployment supported by enabling policy frameworks, targeted investments, and capacity building is critical for unlocking SSA’s hydrogen potential, promoting low-carbon development, and advancing sustainable energy transitions across the region. Full article

Historic cities face a dual challenge of managing waterlogging risks while adhering to strict preservation constraints. Traditional drainage upgrades often require extensive excavation, threatening cultural heritage. This study establishes a quantitative assessment framework for the historic urban district of City B using a 1D-2D-coupled hydrodynamic model (InfoWorks ICM). The model was calibrated using continuous monitoring data, achieving a Nash–Sutcliffe Efficiency (NSE) of 0.91. Its spatial accuracy was subsequently validated against historical waterlogging records, showing a strong consistency between simulated flood-prone areas and observed flood locations. We simulated waterlogging distribution under rainfall events with return periods of 0.5 to 5 years. Results reveal two key deficiencies in the current drainage system under a 0.5-year return period storm event. Firstly, 75.3% of the pipe segments are hydraulically overloaded, failing to meet the design standard. Secondly, this widespread network overload contributes to surface waterlogging, with 9.58 ha (1.80% of the total area) being waterlogged. We evaluated three strategies: Low Impact Development (LID), underground storage tanks, and intercepting sewers. A hybrid grey-green infrastructure (HGGI) system was proposed, integrating source reduction and terminal storage. The HGGI system reduced waterlogged areas by 83.58% (0.5-year event) and 64.87% (5-year event), outperforming single measures. Crucially, this hybrid system achieves minimal intervention in historic street patterns through trenchless construction for intercepting sewers, decentralized LID layout and underground storage tanks, avoiding large-scale road excavation while enhancing flood resilience. This study demonstrates that hybrid strategies can effectively balance flood resilience with environmental and cultural preservation in high-density historic districts. Full article

Since children spend a significant portion of their developmental years in educational settings, the environmental quality of these institutions—specifically, the extent to which they expose their occupants to green space and heat stress—is a critical determinant of well-being and academic performance. This study assesses the green environmental quality of 121 educational institutions (kindergartens, and elementary and secondary schools) in Debrecen, Hungary. The main objective of the research is to identify educational institutions that require immediate intervention to address their lack of green spaces, improve the green environment, and mitigate the urban heat island (UHI) effect. A further aim of the study is to understand how different urban planning practices over the past century have led to the current situation. Therefore, we utilized high-resolution geospatial data (specifically, WorldView-2 imagery) to classify schoolyard vegetation; Landsat data to derive Land Surface Temperature (LST); and the Hoover index to quantify institutions’ spatial concentration. We developed a composite indicator to categorize green environmental quality and heat stress exposure. Our results reveal deep spatial and institutional inequalities. 47.5% of students attend institutions with low environmental quality. While kindergartens typically offer green-rich environments, secondary schools with significant student populations—which are primarily concentrated in the dense historical downtown—are trapped in “grey” zones possessing poor environmental quality. Furthermore, we identify a “green paradox” in socialist housing estates: despite abundant surrounding greenery, schools here record high LST values due to the heat-trapping morphology of vertical concrete structures. The study also highlights institutional maladaptation, such as converting schoolyards into parking lots and using rubber pavements for safety reasons, which contributes to the deterioration of environmental quality. We conclude that current urban planning and school architecture must shift paradigms, treating schoolyards as integral components of the public green infrastructure network through climate-adaptive design. In addition, stakeholders should develop the green environment of educational institutions comprehensively, taking into account both on-site and surrounding green spaces. Full article

With climate change expected to intensify hazards across Europe, empowering communities and strengthening local adaptation is urgent. The challenge is bolstering the resilience of critical infrastructure (CI), which faces substantial risks. Transitioning from predominantly “grey” infrastructure to integrated “green-grey” solutions provides an effective way to safeguard societal and infrastructural assets against hazards and environmental degradation. Although several frameworks developed by international networks and regional authorities exist, they often fail to fully address the nuanced challenges of CI climate proofing, disaster risk reduction, and biodiversity protection. In response to these limitations and to address key societal challenges, the work here introduces an innovative, integrative blueprint framework. This framework synthesises existing approaches to CI climate adaptation, systematically strengthening resilience with nature-based solutions (NBS). The framework is partially applied and validated through the Public-Private-Civil Partnership (PPCP^®) approach, and operationalised in two climatically distinct but heatwave-prone regions: Egaleo (Greece) and Helsinki (Finland). These Labs have promoted more inclusive policymaking by supporting collaboration among key stakeholders, encouraging knowledge sharing and co-designing strategies to advance NBS implementation for heatwave mitigation. The approach facilitated the design of interconnected activities and simplified technical details. Adapting methods to local needs, such as site visits and participatory mapping, has led to concrete outcomes. The prefeasibility analysis outcomes and the targeted NBS-based strategies identified from these areas ensure that solutions are culturally relevant, technically feasible, and collectively owned, incorporating local knowledge and fostering long-term sustainability. Full article

Suburban residential streets have long been criticised for their multiple short-comings, including traffic-related injury, increased stormwater runoff, and lack of aesthetic values. Research suggests that Integrated Green-Grey Infrastructure (IGGI) is likely to play a role in mitigating these problems. IGGI refers to infrastructure that consists of both natural materials (such as plants, soil) and human-made structures (such as concrete, pipes). However, IGGI’s definition remains vague, and little is known about its implementation in suburban street retrofitting, and how effective it is. Using a systematic literature review method, this paper analyses peer-reviewed journal articles published over a period of ten years between 2014 and 2023. The objective was to understand IGGI’s definition, integration, and effectiveness in implemented residential street retrofitting projects. Through a rigorous screening process, 15 papers were selected for qualitative analysis. Clusters developed in analysing the results consist of IGGI’s concepts, components, integration and effectiveness. The most notable subject area is system-scale integration, shared by 14 papers. Findings regarding the effectiveness of IGGI suggest strong empirical evidence related to stormwater management and road user behavioural change; however, there were mixed perceptions toward the aesthetic values of rain gardens. Full article

The Netherlands is widely recognised as the global leader in water management, with its flood risk management (FRM) infrastructure lauded as being of the best in the world. This status notwithstanding, Dutch FRM primarily maintains established infrastructural practices and experimental applications of NBSs remain less frequent than established structural projects. This paper details and examines the challenges associated with the prevailing ‘business-as-usual’ approach to FRM in The Netherlands, in which traditional ‘grey’ infrastructural techniques are prioritised over innovative ‘green’ nature-based solutions (NBSs). In line with emerging international trends, such as the EU Water Resilience Strategy, NBSs are increasingly advocated as a strategic, complementary layer to enhance the resilience of existing safety frameworks rather than a self-evident replacement for them. Contrary to grey infrastructure, NBSs provide a number of environmental and social co-benefits extending beyond their flood and drought protection utility. The literature on NBSs details the design, effectiveness, and positive socio-economic impact of the operationalisation of such projects for FRM. This notwithstanding, the uptake and practical implementation of NBSs have been slow in The Netherlands. From a legal and policy perspective, this has been attributed to a lack of political will and the corresponding failure to include NBSs in long term FRM planning. Given the long planning horizons associated with FRM (50–100 years), the failure to incorporate NBSs can lead to policy lock-in that blocks future adaptations. Against this backdrop, this paper employs a semi-systematic literature review to clarify the obstacles to implementing NBSs in Dutch FRM and sets a research agenda that charts a course to mainstreaming NBSs in Dutch FRM. Seven core focus areas for future research are identified. The paper concludes by drawing on these identified focus areas to construct a research agenda aimed at systematically addressing each barrier to the practical operationalisation of NBSs in Dutch FRM, emphasising a hybrid green–grey approach which may serve to inspire similar research in other jurisdictions. Full article

Rapid urbanization and climate change have intensified flood risk and ecological degradation along urban riverfronts. Recent literature suggests that combining green and grey infrastructure can enhance resilience while delivering ecological and social co-benefits. This study analyzes and compares five riverfront projects in China and Spain, assessing how their tactic mixes operationalize three urban flood-resilience strategies—Resist, Delay, and Store/reuse—and how these mixes translate into ecological, social, and urban impacts. A six-phase framework was applied: (1) literature review; (2) case selection; (3) categorization of resilience strategies; (4) systematization and typification of tactics into green vs. grey infrastructure; (5) percentage analysis and qualitative matrices; and (6) comparative synthesis supported by an alluvial diagram. Across cases, Delay emerges as the structural backbone—via wetlands, terraces, vegetated buffers, and floodable spaces—while Resist is used selectively where exposure and erodibility require it. Store/reuse appears in targeted settings where operational capacity and water-quality standards enable circular use. The comparison highlights hybrid, safe-to-fail configurations that integrate public space, ecological restoration, and hydraulic performance. Effective urban riverfront resilience does not replace grey infrastructure but hybridizes it with nature-based solutions. Planning should prioritize Delay with green systems, add Resist where necessary, and enable Store/reuse when governance, operation and maintenance, and water quality permit, using iterative monitoring to adapt the green–grey mix over time. Full article

Urban Water Systems (UWS) are complex infrastructures that interact with energy, food, ecosystems and socio-political systems, and are under growing pressure from climate change and resource depletion. Planning circular interventions in this context requires system-level analysis to avoid fragmented, siloed decisions. This paper develops the Hydrosocial Resource Urban Nexus (HRUN) framework that integrates hydrosocial thinking with the Water–Energy–Food–Ecosystems (WEFE) nexus to guide UWS design. We conduct a structured literature review and analyse different configurations of circular interventions, mapping their synergies and trade-offs across socioeconomic and environmental functions of hydrosocial systems. The framework is operationalised through a typology of circular interventions based on their circularity purpose (water reuse, resource recovery and reuse, or water-cycle restoration) and management scale (from on-site to centralised), while greening degree (from grey to green infrastructure) and digitalisation (integration of sensors and control systems) are treated as transversal strategies that shape their operational profile. Building on this typology, we construct cause–effect matrices for each intervention type, linking recurring operational patterns to hydrosocial functionalities and revealing associated synergies and trade-offs. Overall, the study advances understanding of how circular interventions with different configurations can strengthen or weaken system resilience and sustainability outcomes. The framework provides a basis for integrated planning and for quantitative and participatory tools that can assess trade-offs and governance effects of different circular design choices, thereby supporting the transition to more resilient and just water systems. Full article

Climate change is altering hydrological regimes across the North Aegean and Marmara regions of Türkiye, with increasing relevance for both drought occurrence and flood generation. This study examines long-term variability in temperature, precipitation, and evaporation using meteorological observations over a long time series and relates these changes to urban water management issues. Daily records from 12 meteorological stations, with data availability varying by station and extending back to 1926, were analysed using the non-parametric Mann–Kendall trend test and Sen’s slope estimator. The results indicate statistically significant warming trends across all stations, with several locations recording daily maximum temperatures exceeding 44 °C. Precipitation trends exhibit pronounced spatial heterogeneity: while most stations show decreasing long-term tendencies, others display unchanging or non-significant trends. Nevertheless, extreme daily rainfall events exceeding 200 mm are observed at multiple coastal and island stations, indicating a tendency toward high-intensity precipitation. Evaporation trends also vary across the region, with increasing rates at stations such as Tekirdağ and Çanakkale and decreasing trends at Bandırma and Yalova, reflecting the influence of local atmospheric conditions. Taken together, these findings point to a coupled risk of intensified flooding during short-duration rainfall events and increasing water stress during warm and dry periods. Such conditions challenge the effectiveness of conventional grey infrastructure. The results are therefore interpreted within the framework of the Sponge City approach, which emphasizes permeable surfaces, decentralized storage, infiltration, and the integration of green and blue infrastructure. By linking long-term hydroclimatic trends with urban design considerations, this study provides a quantitative basis for informing adaptive urban water management and planning strategies in Mediterranean-type climate regions. Full article

Combined sewer overflow (CSO) pollution threatens urban water environments, yet optimizing integrated green–grey infrastructure solutions remains computationally intensive, often making robust, large-scale multi-algorithm comparisons impractical. This study’s primary contribution is the development of an innovative physics-guided optimization framework that overcomes this computational barrier. By coupling a deep learning surrogate (trained on 60,000 scenarios generated in 7.7 h) with evolutionary algorithms, this framework provides a 6.2- to 7.7-fold acceleration in total project time (approximately 13 h vs. 80–100 h) compared to direct SWMM optimization. This significant speedup enabled a comprehensive comparative analysis of four multi-objective evolutionary algorithms (MOEAs), which established NSGA-II’s superiority in discovering a larger and more diverse set of optimal trade-off solutions. The physics-guided surrogate achieved an R² of 0.9965 and a Mean Absolute Error (MAE) corresponding to 0.5% of the baseline overflow volume. The validated framework successfully identified Permeable Pavement as the dominant control variable and a critical knee-point scenario. This solution, requiring a 426 million CNY investment, achieved a 67.0% overflow volume reduction and a 74.4% COD load reduction under the 5-year design storm. Furthermore, the optimized system demonstrated high resilience to extreme events, contrasting sharply with the failure of a cost-minimized approach, which underscores the importance of designing for resilience. This framework provides urban planners with a validated, efficient, and reliable methodology for designing resilient, cost-effective CSO control systems. Full article

Accelerating urbanization and the intensifying pace of climate change have heightened the occurrence of urban pluvial flooding, threatening urban sustainability. As the preferred approach to urban stormwater management, coupled gray and green infrastructure (GI–GREI) integrates GREI’s rapid runoff conveyance with GI’s infiltration and storage capacities, and their siting and scale can affect life-cycle cost (LCC) and urban drainage system (UDS) resilience. Focusing on Fengxi New City, China, this study develops a multi-objective optimization framework for the GI–GREI system that integrates GI suitability and pipe-network importance assessments and evaluates the Pareto set through entropy-weighted TOPSIS. Across multiple rainfall return periods, the study explores optimal trade-offs between UDS resilience and LCC. Compared with the scenario where all suitable areas are implemented with GI (maximum), the TOPSIS-optimal schemes reduce total life-cycle cost (LCC) by CNY 3.762–4.298 billion (53.36% on average), rebalance cost shares between GI (42.8–47.2%) and GREI (52.8–57.2%), and enhance UDS resilience during periods of higher rainfall return (P = 20 and 50). This study provides an integrated optimization framework and practical guidance for designing cost-effective and resilient GI–GREI systems, supporting infrastructure investment decisions and climate-adaptive urban development. Full article

Amid the rapid evolution of the digital economy reshaping global competitiveness, China has advanced regional coordination through the Digital China initiative and the “Data Elements ×” Three-Year Action Plan (2024–2026). To further integrate digital transformation with high-quality growth in the urban agglomerations of the middle and lower Yellow River, this study aims to strengthen regional competitiveness, expand digital industries, foster new productivity, refine the development pathway, and safeguard balanced economic, social, and ecological progress. Taking the Yellow River urban clusters as the research object, a comprehensive assessment framework encompassing seven subsystems is established. By employing a mixed-weighting approach, entropy-based TOPSIS, hotspot analysis, coupling coordination models, spatial gravity shift techniques, and grey relational methods, this study investigates the spatiotemporal dynamics between the digital economy and high-quality development. The findings reveal that: (1) temporally, the coupling–coordination process evolves through three distinct phases—initial fluctuation and divergence (1990–2005), synergy consolidation (2005–2015), and high-level stabilization (2015–2022)—with the average coordination index rising from 0.21 to 0.41; (2) spatially, a persistent “core–periphery” structure emerges, while subsystem coupling consistently surpasses coordination levels, reflecting a pattern of “high coupling but insufficient coordination”; (3) hot–cold spot analysis identifies sharp east–west contrasts, with the gravity center shift and ellipse trajectory showing weaker directional stability but greater dispersion; and (4) grey correlation results indicate that key drivers have transitioned from economic scale and infrastructure inputs to green innovation performance and data resource allocation. Overall, this study interprets the empirical results in both temporal and spatial dimensions, offering insights for policymakers seeking to narrow the digital divide and advance sustainable, high-quality development in the Yellow River region. Full article