Nature-based solutions (NbS) like urban trees, green roofs and restored rivers can protect against climate change impacts like heat and flooding – but they also deliver many further benefits. Yet, these benefits often remain invisible in budget decisions. This guide, which was compiled by the Ecologic Institute and published by the German Environment Agency, shows how municipalities can systematically identify, assess and compare the costs and NbS.

Why assess costs and benefits of NbS?

NbS often require high upfront investment and ongoing maintenance. Compared with technical ("grey") measures, they therefore often appear too expensive. At the same time, they provide numerous co-benefits, for example, for health, biodiversity, recreation and climate mitigation. A systematic cost-benefit assessment weighs these (added) values against investment and maintenance costs. It thus provides a sound basis for prioritising measures and can provide arguments that can help to secure funding.

The guide takes users through a stepwise process on how to go about assessing costs and benefits. Documentation tables and guiding questions help apply each step to a specific project; additionally, an example on retention green roofs in a residential neighbourhood illustrates the application.

Three methods compared

The guide presents three common methods, along with their strengths and limitations:

• Cost-benefit analysis: expresses costs and benefits in monetary terms.
• Multi-criteria analysis: deploys scores and also includes criteria that are hard to monetise, such as acceptance or equity.
• Cost-effectiveness analysis: compares measures with a similar intended effect.

Next to a theoretical overview of each method, practical examples illustrate their application.

Guidance for municipal practice

The guide also includes an overview of current investment and maintenance cost rates for common NbS. Additionally, it explains approaches to monetisation and points to databases, tools and further guidance. It is aimed at climate adaptation managers, planners and other municipal stakeholders.