Cost-benefit analysis of two rain gardens in Stockholm : The role of Sustainable drainage systems in stormwater management

Sammanfattning

Climate change is expected to increase the intensity of cloudbursts, as evidenced by recent events in Gävle (2021) and Malmö (2014), which caused significant damage.This highlights the urgent need for improved flood protection in urban areas. In this context, Nature-based Solutions (NbS) present an opportunity to offer flood protection while enhancing urban landscapes with various co-benefits. A Cost-Benefit Analysis (CBA) was performed on two newly established rain gardens in Östermalmsgatan and Jarlaplan, inaugurated in 2025. The analysis considered factors such as flood protection efficiency, carbon footprint, air and water qualities, noise attenuation, regulation of temperature and humidity, recreational and educational values. These benefits were compared with the upfront and maintenance costs. The Net Present Value (NPV) of the rain gardens was found to be negative due to high capital costs and insufficient flood protection. Additionally, the carbon footprint was considerably negative, with carbon capture benefits massively outweighed by the emissions associated with construction. Despite this, the rain gardens increased property values, partially remediated water and air pollution, improved biodiversity, and provided educational value. While these SuDS offer several environmental and social co-benefits, they were found cost-inefficient as flood protection solutions in an already densely built city fabric, but participate in the city development. Although cost-efficiency is easier to achieve with SuDS in new development areas, they are no magic solutions in city centres, and a balance must be found between architectural constraints, flood protection efficiency and costs.