When nature-based stormwater solutions fall short and how cities can do better

Urban nature-based solutions (NBS) are increasingly promoted as a climate-smart alternative to conventional grey infrastructure for reducing flood risk and supporting greener, more liveable cities. They are expected to do much more than store and absorb rainfall or filter runoff. Because space in cities is limited and expensive, these measures should deliver multiple co-benefits. These can include improved water quality, urban cooling, enhanced biodiversity and more pleasant living environments.

At the same time, research shows that NBS are not always a cure for all challenges. Their promised advantages, particularly in terms of cost efficiency and added co-benefits, are not always clearly demonstrated. This is partly because some solutions underperform, but also because cities often lack consistent ways to measure, track and evaluate many of these benefits over time. Both performance gaps and evaluation challenges are closely linked to decisions made at different stages of a solution’s life cycle, from early planning and design to long-term operation and maintenance.

Full life cycle perspective

Partners of the City Blues project set out to examine when and why nature-based stormwater solutions tend to fail or underperform across their entire life cycle. The study reviewed existing research to identify recurring failure modes from early planning and design through to operation and maintenance. This life-cycle perspective matters because many decisions that shape long-term performance are made long before a solution is built.

The analysis considered local and geographical conditions, recognising that climate, location and project setting influence outcomes. Reported problems were classified based on their severity, origin and preventability, and linked to the life-cycle stage where they occur. All assessments focused on whether solutions continued to meet their intended stormwater functions, such as runoff control, retention and infiltration.

Catchment-scale planning helps prevent later failures

The analysis revealed that the most frequent and critical problems were linked to the earliest stages of a project, particularly planning and design. These include issues such as unclear objectives, poor site selection, limited understanding of local conditions or weak coordination between stakeholders. These early-stage failures are especially important because they are often preventable, yet their effects tend to persist throughout the project’s lifetime.

One key insight is the importance of thinking beyond individual sites. Planning nature-based solutions at the catchment scale can help align local measures with upstream and downstream conditions and reduce the risk that early problems cascade into later stages of design, operation and maintenance. This broader perspective is especially important under changing climate conditions, as more intense and unpredictable rainfall increases the risks associated with fragmented, site-level solutions.

In later stages, challenges shift towards operation and maintenance, where problems are more often linked to insufficient upkeep, changing urban landscapes or evolving climate conditions. While these issues are harder to fully control, their impacts can be reduced if they are anticipated during earlier project stages.

What this means for cities?

Overall, the findings show that failures rarely stem from a single technical flaw. Instead, they emerge from a combination of decisions, assumptions and constraints that accumulate across the life cycle. When early-stage weaknesses are not addressed, they increase the likelihood of underperformance and limit the ability of NBS to deliver both stormwater control and wider urban benefits.

For cities, the results underline that successful nature-based stormwater solutions depend as much on planning and long-term thinking as on technical design. Many serious problems can be avoided by setting clear objectives early, understanding local conditions and considering operation and maintenance from the start. Taking a life cycle and catchment-scale perspective can help cities use limited space and resources more efficiently and increase confidence that nature-based solutions will deliver their promised benefits over time.

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