Ivar Annus & Murel Truu: Urban water management needs joint operation

Across Europe, cities have become increasingly vulnerable to pluvial flooding — from Copenhagen to Valencia, extreme rainfall events have revealed the limits of traditional, static, and monofunctional drainage systems. The infrastructures that were designed for predictable conditions now face accelerating climate variability, rapid urbanization and often struggle with legacy practices and rigid governance frameworks that lack flexibility and adaptation.

To increase the flexibility and functionality of the urban water assets, nature-based solutions (NBS) have become widely promoted in EU, national and regional climate adaption policies. They are expected to perform as one cure-for-all mitigation measures to reduce flood risks, droughts, improve water quality and citizen well-being. Yet in practice, NBS are often treated as isolated, plot-scale interventions — green roofs, rain gardens, ponds — rather than components of an interconnected urban watershed system. As a result, their full potential remains underused, and benefits such as water quality enhancement, ecosystem connectivity, equity, and health benefits are not achieved. This fragmented approach, coupled with a lack of a full life cycle perspective, limits their effectiveness.

Recent analysis on NBS failures have pointed out that cities do not have clear pathways and suitable frameworks to consider the multifunctionality, connectivity and social equity when planning the solutions to mitigate climate-caused risks and to ensure the other potential benefits like increasing the biodiversity and overall satisfaction of the citizens. The failures caused mainly by the lack of cooperation between different departments and community will result in an underperformance of the solutions compared to the desired impacts. The failures in the design and operation and maintenance phase on the other hand will cause critical failures of the solutions stressing the importance of collaboration and joint operation throughout the life cycle of the solutions. In summary, the existing NBS projects are often a) planned in isolation from larger watershed context; b) planning is fragmented across departments and throughout the planning process; c) long-term operation and maintenance and stakeholder engagement is undermined.

To overcome these barriers and respond to this complexity, municipalities and academic partners in the City Blues project funded by EU’s Interreg Baltic Sea Region programme are co-developing a joint operational model for NBS (NBS model) to support cities of different sizes, development stages, and capacities. This model aims to make NBS planning, design, operation and maintenance more robust, replicable, and grounded to be suitable for applications in a real urban context. It provides a shared framework for how cities can govern, implement, and maintain NBS systems across the full lifecycle — from concept to retirement.

The NBS model stresses the importance of treating urban watersheds as functional planning units in cities. Every single intervention implemented on a plot or district scale will affect the stormwater management on the sub-catchment. Therefore, it is important to analyze the potential impact (both positive and negative) of the planned solution at a broader scale considering the changes in flow paths and volumes. Catchment scale approach helps to understand where to plan green areas so that they do not need additional watering during dry periods and which solutions and where have the largest effect to improve the climate proof at a single building, district or city.

A key element in reducing the probability of NBS failures is to root the lifecycle thinking approach in the city governance procedures. The NBS model supports the adoption of lifecycle-based thinking fostering cooperation between different departments, community, and stakeholders in all phases including planning, design, operation and maintenance. This ensures that the potential underperformance of the units caused by the fragmentation of the planning process will be mitigated as the key performance influencers at the operation and maintenance phase are considered and communicated with the stakeholders early on.

Recent studies on multi-system intervention planning frameworks for interdependent infrastructures like NBS have shown that effective implementation of such models can lead to up to 25 % cost savings when considering service unavailability costs for infrastructure on a regional scale.

We expect that implementing NBS model will increase the efficiency of single NBS units, ensure multiple benefits besides stormwater management and reduce the costs induced from the potential failures and uncoordinated operation and maintenance practices. Instead of piloting single high-performing NBS in isolation, the model promotes integrated solutions tailored to catchment-scale challenges. By drawing on the transition paths, and the lessons learned from both successes and setbacks of other cities, it supports municipalities in developing resilient and adaptive local models for mainstreaming NBS.

More information:
https://interreg-baltic.eu/project/city-blues
https://nbsmodel.eu