Valuing the wider benefits of raingardens across Scotland

Turning raingarden climate resilience benefits into investment evidence

While the flood management benefits of raingardens are well established, the wider ecosystem services they provide are often harder to quantify. Designed to capture and manage rainfall runoff through the use of planted landscapes, raingardens can improve biodiversity, create attractive public spaces, support health and wellbeing and contribute to climate resilience.

However, these benefits are rarely reflected in traditional investment appraisals, making it more difficult for decision-makers to compare nature-based solutions with conventional hard engineering approaches.

"The flood resilience benefits of raingardens are well understood, but there is less confidence and understanding around the wider benefits these measures can deliver," explains Mott MacDonald senior civil engineer Thomas Findlay. "Developers, local authorities and water companies need to think beyond traditional flood management and consider spaces that deliver multiple benefits even when it isn’t raining."

To address this challenge, the Green Action Trust worked with Mott MacDonald to identify a practical, evidence-based approach that could quantify the wider value delivered by raingardens. The ambition was not only to improve understanding of these benefits but also to translate them into economic terms that could be used to support business cases, funding applications and investment decisions.

"There is an appreciation that decisions are often driven by money. The ambition is not just to help communicate the benefits, but to monetise them as well," says Thomas.

Building the evidence for wider benefits

Following the review of valuation tools Mott MacDonald recommended the Benefits Estimation Tool (ciriabest), developed by the Construction Industry Research and Information Association (CIRIA). Ciriabest calculates the wider benefits of projects and provides a consistent framework for quantifying and monetising outcomes that are often missed in traditional business cases. These include improvements to biodiversity, water quality, carbon sequestration, recreation, education, amenity value and health and wellbeing.

"We weren't trying to develop a completely new method," says Thomas. "We wanted something that was already accepted, robust and practical for the people making decisions. The aim was to make it easy and efficient for someone who's maybe not an economist, such as an engineer, local authority officer or landscape architect."

The team applied the methodology to five raingardens across Scotland to test it in practice. The assessment combined site visits, stakeholder engagement, literature review findings and available project information to understand how the schemes were performing and what benefits they were delivering. Stakeholders included local authorities, community groups, academics and industry representatives, helping to ensure the assessment captured a broad range of outcomes.

The evaluation process involved identifying the benefits most relevant to each site, determining which could be monetised reliably and applying the selected approach to calculate their economic value. This provided the project team with a structured way of recognising the contribution that natural capital and associated ecosystem services make to communities, places and the environment.

At one case study site, Queensland Court and Gardens, the assessment identified almost £3M in monetised benefits over the lifetime of the project, compared with a construction cost of around £2.6M. Health, recreation and amenity delivered the largest share of value, and since the improvements were made, local greenspace use has risen from 35% to 64%, with nearly one-third of residents now spending time outdoors four to seven times a week.

Thomas explains, "Using this type of evidence early in project development can have the greatest influence on decision-making in the planning and design process, helping teams shape infrastructure as genuinely multifunctional interventions from the outset. This approach is helping to deliver blue-green infrastructure design that looks beyond silos to improve water resilience while also calming traffic, enhancing biodiversity and helping create healthier, happier places to thrive."

Recognising what numbers cannot capture

While the study demonstrated the value of monetisation, it also highlighted the importance of recognising benefits that are difficult to quantify. Stakeholder engagement and site assessments showed that outcomes such as community pride, sense of place and social cohesion are often among the most valued aspects of raingardens, yet they remain challenging to capture through existing valuation tools.

The project also identified opportunities to strengthen future biodiversity valuation approaches. Existing methodologies do not always reflect the importance placed on biodiversity by communities, policymakers and organisations seeking to halt nature loss and improve ecological outcomes.

"The valuation studies are probably underestimating biodiversity benefits," says Thomas. "There can be a disconnect between what the research suggests and the level of demand or ambition that exists to improve biodiversity."

The study has concluded that monetisation should be used alongside qualitative evidence and stakeholder insights. Together, these approaches can provide a fuller picture of the impact that nature-based solutions have on places and communities.

Green Action Trust’s impact and evaluation manager Stephen Hughes agrees: "The evidence generated has given us far greater confidence in demonstrating the value of blue green infrastructure and making a compelling case for future investment. Mott MacDonald has delivered a robust yet practical approach that will inform funding decisions, support wider adoption of raingardens, and shape future discussions on the role of nature based solutions across the Central Scotland Green Network and urban sites throughout Scotland."

Glasgow City Region Green Network development officer Rory McLeod adds: "This study provides valuable evidence of the multiple benefits raingardens can deliver for people, nature and climate. By helping stakeholders better understand and articulate that value, it supports more informed decisions about how blue-green infrastructure can contribute to creating healthier, more resilient places. With greater emphasis being placed on the protection and enhancement of blue-green infrastructure through Scotland’s planning system, the findings come at an important time."

This study provides valuable evidence of the multiple benefits raingardens can deliver for people, nature and climate.

Supporting investment in raingardens and wider nature-based solutions

"Hopefully this helps developers, local authorities and water companies think beyond the immediate objective they're trying to solve," adds Thomas. "When those wider benefits are demonstrated clearly and made simpler to understand, it becomes much easier to justify investment in truly multifunctional spaces."

"As organisations look for ways to strengthen climate resilience, enhance biodiversity and create healthier places, this project provides a practical foundation for more confident investment in multifunctional blue-green infrastructure. By making the broader value of raingardens easier to evidence, it can also help funding conversations reflect the full range of outcomes these projects deliver," adds Thomas.