Cost-effectiveness analysis of urban nature-based solutions: A stepwise ranking approach

Despite increasing interest in nature-based solutions, there is still a lack of comprehensive understanding regarding the costs of different types of nature-based solutions and their variations. Cost information is crucial for economic assessments of the viability of nature-based solutions compared to other alternatives. In this paper, we provide an overview of nature-based solutions costs in urban settings, drawing primarily from a literature review of both gray and scientific literature. We present cost estimates for establishing green and blue spaces in urban and peri-urban areas, street trees, green roofs, and green walls. Our findings show that median costs are 56 EUR/m² for green spaces, 73 EUR/m³ for blue spaces, and 201 EUR/m² for green roofs. Furthermore, we demonstrate how an economic assessment can be carried out utilizing the calculated cost estimates while providing a systematic procedure to handle the multiple potential benefits provided by nature-based solutions. We argue that a step-wise ranked cost-effectiveness analysis, based on ranking local policy objectives, is a feasible approach for making informed choices on competing solutions relative to conventional cost-effectiveness analysis and cost-benefit analysis. The proposed approach could prove useful due to its relatively straightforward application and the fact that it does not require the aggregation of multiple benefits into one common measurement or valuation unit.