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Nature-based Solutions for Stormwater Management in the Helsinki Metropolitan Area, Finland – Prerequisites and Good Practices

Submitted by Maaria Parry 27th October 2022 11:22
A drone photo showing a green roof, raingardens in front of the buildings, and permeable surfaces.

The solutions and supporting information presented in the report are intended to facilitate the adoption of nature-based solutions in urban water management, and more specifically in stormwater management. Photo: Mikko Käkelä / HSY


Urbanisation and dense cities lead to an increase of impermeable surfaces that change the natural cycle of water. Water-related hazards are expected to intensify along with climate change increasing annual precipitation and the intensity of individual rain events. In cities, the challenges are related to stormwater, i.e., rainwater or meltwater that is accumulated on soil surfaces, roofs of buildings and other similar surfaces in built areas. Most of the urban infrastructure managing stormwater has been developed in climatic conditions that are different from today’s, calling for more climate resilient stormwater management systems. Approaches that support the natural cycle of water and utilise ecosystems’ functions are increasingly emerging. One way to describe them is nature-based solutions.

The purpose of this report is to identify good practices and solutions for nature-based stormwater management in urban areas, focusing on the Helsinki Metropolitan Area (HMA), Finland, that consists of the cities of Helsinki, Espoo, Kauniainen and Vantaa. The research underpinning this study is based on a literature review, interviews with cities’ staff members and showcasing of selected sites. The report work was carried out as part of the project titled RAINMAN – Towards higher adaptive capacity in urban water management (2019-2021). The project aimed to enhance the capacity of cities and municipalities to cope with climate change impacts such as increasing stormwater volumes especially within urbanised areas. In particular, the report targeted finding solutions at the four land use types defined in the RAINMAN project: green or natural areas, developing or rural areas, densely built-up areas, and historical built-up areas. No solutions were found to be showcased in the historical built-up areas, which only City of Helsinki represents.

The report provides a snapshot of the definitions, types of solutions and co-benefits of nature-based solutions for stormwater management both in the Helsinki Metropolitan Area and globally. It also presents aspects related to monitoring and maintenance as well as governance structures and strategies through eight solution sites selected for the study. Therefore, it examines both solutions and the prerequisites of cities to implement such solutions. Based on the findings, the report discusses factors facilitating and hindering nature-based solutions for stormwater management.

Nature-based (or natural) stormwater management has largely become established due to the national level stormwater legislation and city-level stormwater management programs. The stormwater working groups in the HMA cities appear to be well aware of the nature-based solutions and play an important role in advancing such solutions.

The stormwater management solutions in the HMA cities were often found to be hybrid solutions, including both “green” and “grey” infrastructure. Nature-based solutions provide several other benefits in addition to managing the stormwater quantity and quality such as supporting biodiversity, increasing aesthetic and recreational values, and reducing heat island effect. However, it appears that identification and monitoring of such benefits is in most cases limited. This hinders assessing the impact of nature-based solutions that is essential to support evidence-based land use planning and policymaking.

This weADAPT article is an abridged version of the original text, which can be downloaded from the right-hand column or accessed in an accessible (and mobile-friendly) online version. Please access the original text for more detail, research purposes, full references, or to quote text. 

Aims of the report

The main aim of this report is to identify good practices and solutions to green or nature-based stormwater management in urban areas, focusing on the Helsinki Metropolitan Area (HMA). This is to reduce negative impacts of stormwater on freshwater resources, targeted at the four land use types defined in the RAINMAN project.

The RAINMAN project is based on an assumption that nature-based solutions can be easier to implement in developing areas but on densely built-up or historical areas novel solutions might not be possible to realise and traditional methods to handle stormwaters are more feasible. Therefore, a decision was made at the outset of the project to specify solutions for different land use types that have comparable characteristics in Finland. It was agreed to divide solutions in four different categories: green or natural areas, developing or rural areas, densely built-up areas, and historical built-up areas. Analysing similar land use types in the project case study areas enables sharing best practices and cross-border learning in common challenges.

The results of this work can benefit both the RAINMAN project partners as well as wider audience in other urban areas, especially professionals working on urban water management issues.

This report intends to respond to the following questions:

  • How is a "green" or "nature-based" stormwater management solution defined?
  • What are the good practices and solutions to stormwater management in the Helsinki Metropolitan Area’s cities?
  • Are certain types of solutions favoured?
  • Which kinds of solutions are planned at the moment?
  • What are the co-benefits?
  • How are these solutions monitored or maintained?
  • What types of governance structures or strategies cities have have adopted or put in place?
  • What factors have facilitated these solutions, and what obstacles still remain?

A rainwater basin in a park with some stones in the clear water. In the background there is a low dam with an overflow spillway and behind it, there is a pedestrian bridge.

Photo: Mikko Käkelä / HSY

Materials and methods

The research underpinning this report is based on a literature review, interviews and photography of selected sites. The research was carried out mainly in February – November 2021. The review of literature included various types of peer-reviewed and ‘grey’ literature, such as cities’ stormwater management programs and other relevant publications (e.g. maps), publications related to nature-based solutions, relevant project reports, journal articles, theses as well as the RAINMAN project material. Given the increasing amount of literature published on the topic of nature-based solutions and urban water management, this review is not intended to be exhaustive but provides a snapshot of current research, practices and lessons learnt in the field.

The literature review was complemented by semi-structured interviews with staff members of all four HMA cities.

Facilitating factors for NbS

Based on the findings presented in this report, following points are determined as facilitating factors or drivers for such solutions:

  • There are national-level steering measures and legislation in place that support integrated and nature-based stormwater management, including requiring municipalities to develop integrated stormwater management in areas where a local detailed plan is in force.
  • City-level stormwater management programs dictate that the management, treatment and conveying of stormwater follows the priority order set by the national level stormwater legislation. They also recognise the values beyond stormwater quantity and quality management.
  • There is a dedicated body, like a stormwater management working group including all relevant actors and ensuring seamless communication and cooperation on stormwater management issues.
  • Green Factor and Green Efficiency tools, such as those used in Helsinki and Vantaa, support the aims to increase green areas and nature-based solutions in the city.
  • The process of developing a nature-based stormwater management solution considers monitoring and maintenance (e.g. by directing funds and including the maintenance staff and other essential personnel at an early stage).
  • Stormwater management data is organised into a city-level maintenance card file (such as in Vantaa and Espoo) that can help keep track of maintenance needs and offer ways to develop old operation models.
  • Monitoring and impact evaluation of nature-based solutions are essential to be able to determine their success, as well to support evidence-based land use planning and policy-making. They also support increasing the understanding of the benefits and trade-offs of nature-based solutions.
  • Documenting and sharing both successes and failures in implementing nature-based solutions can serve as learning for others, increase the understanding of the various solutions’ function, and strengthen cooperation among various actors.
  • Increasing amount of impermeable surface and densification aims lead to a lack of space to implement nature-based solutions. However, when changing the purpose of areas, for instance, when industrial areas are converted to residential areas, there is a chance to remove impermeable surfaces and replace them with green areas and nature-based solutions. Also roof spaces can offer opportunities to introduce nature-based solutions.
  • Hindering factors like community opposition can already be solved in the design phase when the local context and aim of the stormwater management structures are carefully considered.