Matilda Gunnarsson & Karina Barquet: Nature-based solutions in Swedish stormwater management

Expansion and densification of urban areas, in combination with the effects of climate change on precipitation patterns and intensity, make cities sensitive to flooding. This calls for stronger and earlier integration of climate adaptation measures in spatial planning and stormwater management.

In response, the Swedish government has set two key milestones within its environmental goals framework to enhance sustainable stormwater management:

1. By 2023, all municipalities must integrate sustainable stormwater management into the planning of new buildings or significant modifications to existing structures.
2. By 2025, municipalities at risk of significant stormwater impacts on soil, water and the built environment must complete a mapping process, develop action plans for sustainable stormwater management and begin implementation.

Sustainable stormwater management prevents stormwater runoff, treats polluted stormwater, supports urban ecosystem services and adapts to a changing climate. A common approach is to use Nature-based Solutions (NbS), described as multifunctional and cost-effective solutions addressing societal challenges by protecting or developing ecosystems while promoting biodiversity and well-being.

Although NbS are recognised solutions for sustainable stormwater management, challenges remain in planning, procurement and implementation. These challenges are often socio-institutional rather than technical. Uncertainties in responsibilities, financing, costs and knowledge contribute to delays in adoption. Moreover, evidence on how co-benefits and multifunctionality are perceived remains limited.

Based on this, within the HydroHazards project, we examined cost estimates for NbS, the extent to which co-benefits are included in Swedish municipal stormwater guidance, and their alignment with policy.

Availability of cost estimates

There is a general need for more context-specific cost data, along with descriptions of what these costs include. Costs of NbS vary depending on where and how they are implemented. Factors like size, design, context and the aim to deliver additional benefits influence costs for both implementation and operation and maintenance (O&M). Estimates of intervention costs are often uncertain, and detailed O&M costs are rare.

Inclusion of NbS in municipal steering documents for stormwater management

NbS are incorporated into stormwater management in Sweden. The specific term “nature-based solutions” is not however widely used in municipal stormwater documents. Instead, terms like “open”, “local”, “green and blue”, “sustainable” and “multifunctional solutions”, as well as examples of specific NbS are highlighted as preferred approaches for managing stormwater.

Generally, municipal stormwater documents address co-benefits, and most of these documents make reference to multifunctional stormwater solutions. However, the co-benefit coverage varies. Flood risk control, water quality, biodiversity, aesthetics and health are frequently mentioned; while heat island effect, carbon sequestration, air quality, energy consumption and noise reduction are only included to a limited extent.

Responsibilities in municipal stormwater management

Municipalities recognise the importance of clarifying responsibilities for stormwater management, but the level of detail and thoroughness varies. The division of responsibilities for stormwater management is complex, with no single actor holding full authority. Different actors, both within and outside municipal government, influence the overall stormwater management. Responsibility across the full life cycle of NbS should therefore be defined early, including O&M and associated costs, especially for shared solutions.

Alignment with policy

There is strong regulatory and policy support for the implementation of NbS and/or potential co-benefits. Despite the strong support, regulatory and policy frameworks often insufficiently recognise the multiple co-benefits of NbS. This can undermine the monetary and non-monetary value, and the business case. Regulatory and policy development that accounts for multifunctionality is needed to accelerate uptake.

Moving forward

A more mainstream and consistent approach to quantifying and tracking costs, especially for long-term operation and maintenance, would strengthen municipalities’ ability to plan, budget, and procure NbS. Our study shows that cost data are scarce and rarely standardized, which limits learning and slows scale-up. Similarly, greater emphasis on the multifunctionality and broader benefits of NbS could strengthen the business case and enable co-financing across sectors. Finally, clearer life-cycle responsibilities and shared service models for multifunctional solutions are needed, particularly where public and private land overlap. Taken together, these findings point to a practical agenda for unlocking wider adoption: shared cost frameworks, consistent evaluation of co-benefits, and governance routines that support long-term delivery.

This text is based on the SEI report “Nature-based solutions in municipal stormwater management in Sweden: costs, co-benefits, responsibilities and policies”.