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In rapidly urbanizing catchments, increase in stormwater runoff may cause serious erosion and frequent floods if stormwater management systems are improper and dysfunctional. Through GIS-based modelling, field investigations, resident’s questionnaire survey, and interviews with officials, the study set out to assesses the coverage and efficiency of drainage infrastructure in Mbezi River catchment basin in Dar es Salaam, Tanzania. Between 2003 and 2016, the catchment imperviousness increased by 41%, causing flood incidents, massive erosion, and numerous pollution sources. Residents strive to address stormwater hazards using terraces, hedges, and physical barriers; however, the problems persist, indicating lack of coordination and poor causality understanding between land-use changes and catchment impacts. Small-scale stormwater harvesting was exercised by 75% of the households, pointing to water supply challenges. Municipal stormwater management efforts was limited to roadside drains covering 17% of road lengths in the catchment, and 65% of those did not meet their design standards. Interviews with officials revealed a need for improved co-understanding and collaborative initiatives to bolster integrated water management. The study suggests a need to adopt a new urban stormwater management paradigm, appropriate for both residents and authorities. Without this new discourse, the urbanization led stormwater increase might jeopardize the liveability of the entire catchment.

Highlights • The adaptive capacity for retaining green infrastructure is weak in both cities. • An understanding of the potential of green infrastructure is emerging. • Retaining green infrastructure has limited power in daily management of urban development. • Experiments involving local communities could enhance the adaptive capacity. Abstract In this paper we examine the conditions and opportunities for establishing a functional green infrastructure under the pressure of urbanization in Addis Ababa and Dar es Salaam. Inspired by transition theory, we look for regimes and niches which support retainment of green space and their adaptive capacity based on interviews and workshops with key urban stakeholders. A top-down master planning paradigm combined with a green institutional framework preoccupied with beautification seem to block possibilities of supporting and integrating GI experiments coming from outside the regime. The master plans are vague, outdated before finalised and inefficient for coping with the fast pace of urbanization. In Addis Ababa, despite an emergent recognition of the role of the green infrastructure in the city plan, informal encroachment and planned large scale land-conversions to housing takes place. In Dar es Salaam, that subscribes to, but lacks a functional master plan, the regime seems paralysed and is too fragmented and engrossed with the pressing urbanization problems to prioritize a green infrastructure. For establishing a functional green infrastructure coalition partners from housing, road and urban agriculture authorities but also large land owners, informal settlers, urban farmers and local organisations are needed. Solutions must be attractive also for the actual green space managers − the individual plot- and condominium owners and local groups. Local niche experiments linking up to on-going coping strategies could push forward coalitions as well as generating knowledge on how to retain green areas while addressing water shortages, livelihood and urban farming. [ABSTRACT FROM AUTHOR]

In the search for both immediate solutions and long-term transitions towards sustainability, green infrastructures (GI) are increasingly linked to urban water management. In this study, the GI-based urban water management practices of five cities famous for their progressive approach to water management were investigated. Based on reviews of open-source city plans and strategies, supplemented with information obtained directly from city managers, the purpose was to share best practices for the transition to sustainable urban water management and to gain insight into the role, if any, of GI in urban water management. An analytical frame based on transition theory was adopted. All five cities represented states of transition at the near end of a sustainable urban water management scale. Despite some overlap in challenges concerning water supply, environmental protection, and flood risk management, the development target of each city was unique, as were their solutions. GI has been applied as a way to reduce water footprints in Singapore and Berlin, to protect the environment in Philadelphia, and to help save potable water for consumption in Melbourne and Sino-Singapore Tianjin Eco-city. Despite differences in scale, GI was, in all cases, applied as a supplement to the conventional water infrastructure. All five cities reveal a strong top-down approach towards sustainable urban water management and a strong mindset on GI's role for future development. However, all five cities point to similar challenges for GI implementation, including space and cost constrains as well as barriers for inter-sectorial and stakeholder collaboration, which limit the speed of city-wide upscaling of GI solutions and full realization of GI benefits. The study indicates a need for a simultaneous change in the cognitive, normative, and regulative conditions of the urban water management regime for sustainability transition. Such a change requires a better balance between top-down and bottom-up planning to overcome barriers and foster innovation. The five cities jointly contribute to a noteworthy list of green solutions, city-wide strategies and guidelines, pilot project programs, regulations, and incentive programs, which may serve as inspiration for other cities' transition plans. [ABSTRACT FROM AUTHOR]

Green roofs are often claimed to provide a range of environmental, economic and social benefits, or ‘ecosystem services’. These reported benefits, suggests that green roofs could play a significant role in sustainable urban development, and consequently green roofs are now widely used as tools in urban planning strategies. Accordingly, it is relevant to assess whether the benefits of green roofs and comparative advantages over conventional roofs rest on a robust evidence base. A considerable number of studies of the ecosystem services delivered by green roofs have appeared over the last few decades, but a rigorous assessment of the overall level of evidence is lacking. Using a systematic review approach, this study seeks to evaluate the documentation relating to three selected green roof ecosystem services: reduction of the urban heat island effect, reduction of urban air pollution, and reduction of building energy consumption. The number of studies quantifying effectiveness with original data was found to vary significantly from service to service: 17 studies reported cooling at street level ranging between 0.03–3 C°, four reported pollution removal at roof level e.g. removal of small particles, PM 10 , ranging between 0.42–9.1 g/m 2 per year, and 41 reported on building energy consumption, of which 20 were comparable and claimed changes in annual consumption ranging between an increase of 7% to a 90% decrease. The large spans in documented effectiveness are ascribed to heterogeneity in context and design parameters of the identified studies. Analysis of the identified studies suggests that some parameters are of key importance for the effectiveness but further research is needed to clarify the complex relation between ecosystem service effectiveness and the parameters influencing it. [ABSTRACT FROM AUTHOR]