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Assessing the Nature-Based Solutions (NBS) contribution to urban resilience, along with developing tools capable of demonstrating their long-term value, comprises a most needed step forward. Nevertheless, the NBS contribution to urban resilience has been yet slightly explored. Given the urban resilience complexity and multiple NBS capabilities, specific needs for a robust assessment should be investigated. This paper identifies the requirements for a comprehensive assessment of the NBS contribution to urban resilience and analyses the main assessment frameworks focused on resilience and NBS for urban drainage. First, the evolution of the resilience concept and relevant resilience assessment frameworks (RAF) are presented. Secondly, NBS challenges to enhance resilience and NBS assessment proposals are analysed. Thirdly, the attributes for assessing urban resilience and aspects to assess the NBS contribution are analysed. To conclude, a critical analysis of the assessment approaches is presented. Important challenges across the RAF have been identified, especially regarding their feasibility of application. Based on the performed analysis, most RAFs are not feasible for city benchmarking and assessing the resilience evolution over time, neither for assessing comprehensively the NBS contribution. Regarding specifically the NBS assessment proposals, just one focused on urban resilience was developed to date, which allows evaluating their contribution over time, between cities, or between different NBS.

Over the past two decades, performance assessment based on performance indicators (PI) has been one of the areas showing the greatest advancement in the water sector. This practice may be defined as any approach that aims to measure effectiveness and/or efficiency of an activity or process using PI, supporting the decision-making process and encouraging the continuous improvement of a water utility. Despite the potential benefits, few projects and initiatives of performance assessment based on PI have been undertaken regarding storm water systems. The present article aims to review studies that have been carried out in the area to provide a state of the art on the subject, understand the applicability of the existing methodologies and their limitations, and to point out future directions. The review revealed that most of the research works were of limited scope, focusing on single storm water systems or some specific aspects of their performance, and also gave an inappropriate definition and selection of PI, compromising their further application. The identified gaps emphasise the need for a new methodology to provide a reference framework in the field. Such methodology should be objective, standardised and well-adapted to different contexts, driven by objectives and criteria and based on PI and targets.

The use of constructed wetlands as a valuable and attractive method for combined sewer overflow (CSO) treatment has been demonstrated in several studies. In Portugal, a Mediterranean country having usually a long dry period, there are still no applications of this technology. The purpose of this research is to gather information and know-how required for the design and management of this type of infrastructure. A pilot-scale experimental setup for CSO treatment was installed and evaluated in situ, in terms of organic matter, total suspended solids and microorganism removal with emphasis on the results of the start-up. After 1 day of retention average removal efficiencies of 73–79% and 82–89% were obtained in terms of chemical oxygen demand (COD) and total suspended solids (TSS), respectively. During the remaining retention time a slower removal was observed. After 7 days, the COD removal efficiencies reached 86–91% and the TSS removal efficiencies reached 93–97%. On average, after 1 day, reductions of 1.2–2.0 log and 1.9–2.4 log, respectively, for total coliforms and Enterococcus were observed. For a retention time of 7 days these reductions attained 4.0–4.9 log and 4.4–5.3 log, respectively.