Due to increased urbanisation, and climate change, there have been calls for a more sustainable management of stormwater. Blue-green measures have been recognised as a sustainable solution and a necessary complement to pipe-bound approaches. The aim of this study is to identify barriers and drivers in the implementation of bluegreen measures in a Swedish context, to increase the understanding of how they could be implemented in a more successful manner. The study is qualitative and based on semi-structured interviews. Through the lens of transition theory, barriers and drivers for blue-green measures were identified and they give an updated picture of Swedish urban stormwater management. Many factors encourage municipal actors to implement blue-green solutions, such as increased need for recreation, protection of biodiversity and climate change. Identified barriers are found within the municipal stormwater management it-self, but can also be found outside the storm water management structure, such as lack of knowledge among politicians, officials, exploiters and civilians, fragmented roles and responsibilities in general, as well as uncertainty of the effects and cost of new alternatives. The study has three main findings; Several barriers were mentioned by most of the interviewees clearly show that a wide range of changes are needed to alter the current stormwater management regime; Niche innovations are often put forward as a way to enhance socio-technical transition, but this study is that such an approach is oversimplified instead elaborated suggestions for an alteration of urban stormwater management is given, both with top-down and bottom-up perspective. For the success of blue-green solutions, educational efforts are important at different levels in the planning, building and maintenance process of blue-green solutions. Therefore, employees must have a good general knowledge of both blue and green issues as well as having contacts in the different sectors of the municipality. To conclude we argue that a transition can not only be induced by pilot projects but requires change in legal structures as well as altered financing models for blue-green solutions. Moreover, the ongoing, but slow, change should therefor probably be interpreted as a shift to a new regime, but rather an evolutionary transition where new approaches are combined with traditional, pipe-bound solutions.

Urban flooding is of growing concern due to increasing densification of urban areas, changes in land use, and climate change. The traditional engineering approach to flooding is designing single-purpose drainage systems, dams, and levees. These methods, however, are known to increase the long-term flood risk and harm the riverine ecosystems in urban as well as rural areas. In the present paper, we depart from resilience theory and suggest a concept to improve urban flood resilience. We identify areas where contemporary challenges call for improved collaborative urban flood management. The concept emphasizes resiliency and achieved synergy between increased capacity to handle stormwater runoff and improved experiential and functional quality of the urban environments. We identify research needs as well as experiments for improved sustainable and resilient stormwater management namely, flexibility of stormwater systems, energy use reduction, efficient land use, priority of transport and socioeconomic nexus, climate change impact, securing critical infrastructure, and resolving questions regarding responsibilities.

Risk management has reduced vulnerability to floods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3.

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To date, the assessment of hydrological climate change impacts, not least on pluvial flooding, has been severely limited by i) the insufficient spatial resolution of regional climate models (RCMs) as well as ii) the simplified description of key processes, e.g., convective rainfall generation. Therefore, expectations have been high on the recent generation of high-resolution convection-permitting regional climate models (CPRCMs), to reproduce the small-scale features of observed (extreme) rainfall that are driving small-scale hydrological hazards. Are they living up to these expectations? In this study, we zoom in on southern Sweden and investigate to which extent two climate models, a 3-km resolution CPRCM (HCLIM3) and a 12-km non-convection permitting RCM (HCLIM12), are able to reproduce the rainfall climate with focus on short-duration extremes. We use three types of evaluation–intensity-based, time-based and event-based–which have been designed to provide an added value to users of high-intensity rainfall information, as compared with the ways climate models are generally evaluated. In particular, in the event-based evaluation we explore the prospect of bringing climate model evaluation closer to the user by investigating whether the models are able to reproduce a well-known historical high-intensity rainfall event in the city of Malmö 2014. The results very clearly point at a substantially reduced bias in HCLIM3 as compared with HCLIM12, especially for short-duration extremes, as well as an overall better reproduction of the diurnal cycles. Furthermore, the HCLIM3 model proved able to generate events similar to the one in Malmö 2014. The results imply that CPRCMs offer a clear potential for increased confidence in future projections of small-scale hydrological climate change impacts, which is crucial for climate-proofing, e.g., our cities, as well as climate modeling in general.

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