ABSTRACT Nature-based stormwater solutions (NBSSs) have originated as a response to urban drainage challenges, offering today a wide range of co-benefits driven by underlying complex ecological processes. As these systems age, concerns about their effectiveness highlight the need for a comprehensive asset management approach. This study aims to (i) uncover the foundations of NBSS asset management research; (ii) examine its evolution over time, particularly in relation to operation and maintenance; and (iii) identify future research needs within the field. Findings reveal that while the concept of asset management is relatively recent for NBSSs, its individual components have been explored since the 1990s, primarily in North America and Australia. Performance – especially water quantity and quality control – has been the dominant focus, often through experimental studies. In contrast, socio-ecological dimensions remain largely theoretical. Rehabilitation and deterioration have gained traction recently, though not yet as central themes. Maintenance is seldom addressed directly, although it frequently intersects with other asset management aspects. Over the past decade, research interest in NBSS asset management has expanded to more than 30 countries and 38 disciplinary fields. This momentum presents an opportunity to foster interdisciplinary studies that integrate all facets of asset management, in order to support NBSS sustainability.

ABSTRACT Green infrastructure such as bioretentions are critical for urban stormwater management. Yet, their performance can degrade over time due to environmental and anthropogenic stressors. Proactive maintenance planning is essential, but often hampered by limited performance data. Without monitoring data or inspection records, proxy indicators offer a practical way to estimate the intensity of external stressors. However, their usefulness depends on selecting relevant proxies and access to suitable datasets. This study uses a two-step decision tree to identify relevant external stressors and select suitable proxies. It also evaluates datasets needed to calculate these proxies for bioretention systems. Twelve stressor categories were identified based on spatial variability and external origin. For 11 of these, 30 proxy indicators were identified from literature, sensitivity analyses, or empirical studies. Norway serves as a case study to assess dataset accessibility and suitability. Some proxies, particularly those related to traffic infrastructure or points of interest, had high-quality open-access datasets. Others were limited or unavailable, highlighting the need for improved institutional data sharing and, potentially, citizen science initiatives. The identified proxies help estimate stressor intensity and support the prioritization of monitoring, inspection, and maintenance. This approach provides a practical framework for improving GI asset management in data-scarce contexts.

ABSTRACT Rural improved sanitation remains a major challenge to achieving the UN SDG 6 goal. In this regard, this study evaluates, with local stakeholders, an operational rural sanitation project in Ouijjane commune, Morocco, using French Reed Bed (FRB) technology. Data from project documentation, as well as field interviews and focus group discussions, were used to carry out a participatory evaluation. The findings reveal, for the monitored period (2020–2021), high organic load reduction with TSS at 85%, COD between 87 and 90%, BOD5 between 85 and 90%, and relatively high TN removal of 75%. While household interviews demonstrate a significant improvement in the sanitary situation, the focus group discussions uncover existing challenges in facility management by the local association and governance barriers. The findings also indicate the importance of postconstruction follow-up and systematic evaluations in rural water projects.

ABSTRACT Extreme rainfall and urban flooding pose escalating risks to public health by mobilizing sewage and pathogenic microorganisms. In July 2021, record-breaking rainfall in Henan Province, China, caused catastrophic flooding, yet the microbial health risks associated with such events remain poorly quantified. Here, we applied high-throughput qPCR arrays to detect 21 pathogenic bacteria in floodwater and postflood tap water, and used quantitative microbial risk assessment (QMRA) to estimate infection probabilities for exposed residents. Our results showed that in floodwater, 21 pathogenic bacteria were detected, with Cryptosporidium spp. (579.8 gc/L) and Pseudomonas aeruginosa (13,500.9 gc/L), being prominent, which were also identified in tap water. Floodwater exposure substantially increases infection risks, highlighting ingestion and inhalation as primary pathways. Simple protective measures, such as avoiding contact with contaminated water, can significantly reduce risks. This study provides the first integrated molecular and risk-based assessment of microbial hazards during an extreme flood event. The findings underscore the importance of water quality monitoring, improved sewage and drainage management, and timely public health interventions such as boil water advisories. As climate change intensifies the frequency of extreme rainfall events, proactive surveillance and international collaboration will be essential to prevent waterborne disease outbreaks and protect vulnerable populations.

ABSTRACT To assess the reliability of green stormwater infrastructure (GSI), including grass swales, it is required to characterize the frequency of system failures. This involves identifying the conditions when the system operates in failure mode, potentially causing downstream flooding. The study utilized three 23-year meteorological time series from three Swedish locations, characterized by frontal, convective, or orographic rainfall events. These time series served as inputs for the simulation of runoff flows using the SWMM model, representing the physical characteristics of a grass swale (GS) located in Luleå, Sweden. Results showed a trend of reduced overflow occurrences and flood risks at higher ksat values of 25 and 31 mm/h. Exceedance curves indicated that ksat values of 2 or 4 mm/h resulted in the swale operating in failure mode 100% of the time. A minimum ksat of 31 mm/h was required to achieve acceptable operation for more than 50% of the time in Gothenburg and Luleå. Östersund was the only location where the studied GS did not operate in failure mode under a high ksat of 31 mm/h. Local climate – especially rainfall distribution and frequency – sets performance thresholds and underscores the need to integrate technical performance with flood risk management in GSI design.

ABSTRACT Tropical freshwater reservoirs are vital for water management but also contribute to greenhouse gas (GHG) emissions, making mitigation strategies crucial, especially in the Brazilian Northeast, where water scarcity and climate variability impact livelihoods and ecosystems. This semi-arid region depends on reservoirs due to irregular rainfall and high evaporation, with reforestation offering a promising means to offset emissions while supporting sustainable water management. We assessed the carbon footprint and offsetting potential of 24 small reservoirs in the region using the G-res tool under SSP2-4.5 and SSP5-8.5 climate scenarios. Results show that GHG emissions vary with water depth, climate, and land use, with smaller reservoirs often showing higher emissions. Expanding vegetation in catchments and around reservoirs can help offset emissions and enable blue-green transitions for climate change mitigation. Future reforestation efforts must increase significantly, requiring a 286% rise in forested areas compared with the reference period under the SSP5-8.5 scenario to fully offset emissions. By analyzing emissions from reservoirs and applying reforestation to reduce their carbon footprint, this study shows that (1) climate change and unsustainable transitions raise GHG emissions in tropical reservoirs, (2) reforestation can offset emissions and support sustainable management, and (3) future reforestation areas must expand under climate scenarios.

ABSTRACT Urban areas are becoming increasingly vulnerable to climate change due to shifting rainfall patterns. This study investigates adaptive strategies for stormwater management by integrating green and blue infrastructures (GBIs) under extreme climate uncertainty. A novel framework based on the analysis of reality in options (RIO) and GBIs, called (RIO-GBI), is introduced, which uses probabilistic climate modeling and dynamic decision-making to develop flexible adaptation strategies. A case study in Gorgan, Iran, applied the SSP245 climate scenario and the MRI-ESM2 model to project rainfall changes across three future periods (2025–2050, 2051–2075, and 2076–2100). The results indicate a decline of 8.48% in average precipitation during 2025–2050 compared with 2001–2024, followed by increases of 13.10% in 2051–2075 and 20.72% in 2076–2100. Using a geometric Brownian motion process, 27 plausible climate scenarios were generated and ranked by probability, with the three most likely pathways identified at 26.67, 19.81, and 10.20%, respectively. The findings highlight the effectiveness of combined GBIs, such as infiltration trenches, retention ponds. These strategies enhance urban resilience by improving stormwater management, reducing flood risks, and supporting sustainable urban development. Nevertheless, uncertainties in climate projections underscore the need for integrated uncertainty analysis in urban planning to ensure long-term adaptability.

ABSTRACT This study presents the Pingjiang River Water Purification Project in Suzhou, a historic city facing water quality challenges due to urbanization. The project integrates advanced physical treatment techniques to restore water quality and ecological health while preserving the city's cultural heritage. The core component, the water purification plant, employs hollow-fibre ultrafiltration membrane technology to treat river water, achieving significant reductions in turbidity, suspended solids, total phosphorus, and chroma, along with improved transparency. Additionally, the plant's underground layout minimizes the land footprint, while sludge generated through the process is repurposed for brick manufacturing, supporting resource recovery. This study conducts a life cycle assessment to evaluate the environmental impacts of the plant's water purification process. Results show that electricity consumption, polyaluminium chloride, and sodium hypochlorite are the top contributors to environmental impacts, with a global warming potential of 0.207 kg CO2 eq/m3. However, the plant also offsets impacts through phosphorus removal and sludge reuse. Recommendations include optimizing chemical inputs, improving energy efficiency, and integrating renewable energy. The findings highlight the project's role in balancing water quality improvement with environmental tradeoffs and co-benefits, providing insights for sustainable urban river restoration in culturally significant contexts.

ABSTRACT Urbanization and climate change are putting pressure on urban drainage systems, particularly in cities with aging combined sewers. This study evaluates the effectiveness of green infrastructure (GI) in reducing combined sewer overflow (CSO) durations and pollutant loads under current and future climate conditions. Using a spatially realistic, stakeholder-informed implementation approach, the study addresses modelling uncertainty, evaluation of practical GI implementation strategies, and identifies subcatchments contributing to pollutants in the overflow. An ensemble-based hydrological model and a simplified pollutant load assessment were applied to an urban case study in Trondheim, Norway, using scenarios developed in collaboration with local stakeholders to implement bioretention cells in the catchment. Results showed that GIs limited to public land can reduce CSO durations by up to 63% under the current climate and 65% in the future climate. Evaluation of pollutant loads from critical subcatchments highlighted areas for additional water quality benefits. The study demonstrates that stakeholder-informed modelling provides practical insights for municipalities and supports the development of integrated stormwater management plans.

ABSTRACT The presence of pharmaceuticals and personal care products (PPCPs) in drinking water has garnered increasing attention due to their negative effects on human beings. However, it's still unclear if they can transport from source water to tap water. This study investigated the occurrence and fate of 44 PPCPs in seven full-scale drinking water treatment plants in a typical industrial city of Southwest China. The total concentrations of PPCPs were 72.4–477 ng/L in source water, with caffeine (up to 177 ng/L) and its metabolite of 1,7-dimethylxanthine (49.1 ng/L) dominating. Water treatment processes removed about 14% of PPCPs, while coagulation–sedimentation contributed 22% of the removal. The removal efficiencies were significantly varied when using different source waters, i.e., river water and reservoir water sources. Hydrophilic compounds with Log KOW < 2 exhibited desorption during filtration, resulting in a 53% rebound in penicillin antibiotic concentrations. All PPCPs showed health risk quotients (RQH) below the safety threshold (0.01), with penicillin-G posing the highest risk to infants (RQH = 4.52 × 10−3). The study highlighted conventional treatment limitations for the removal of PPCPs, which showed the importance of selecting water treatment processes optimized based on source water characteristics.