A valuation of ecosystem services from blue-green infrastructure for stormwater management

Abstract: The ongoing urbanization leads to densification and growth of cities, which replaces natural areas with hard surfaces. Precipitation is then more likely to runoff as stormwater than to be detained locally. Also, precipitation is predicted to be increasing as an effect of climate change. Traditionally, stormwater has been handled by draining it in underground pipes. As a complement, blue-green infrastructure (BGI) can be used to take care of the increased amount of stormwater. BGI is vegetation and water-based systems that intend to restore the natural flows of water. It does, however, not only provide services for stormwater management but also other services that contribute to human welfare. These are provided for free by nature and are called ecosystem services. By illustrating the value of ecosystem services, the motivation of implementing more BGI can increase. The aim of this project was to provide guidance on how to value ecosystem services that BGI can provide at a district level. The valuation was to be semi-quantitative with the grades 1-5. To do so, ecosystem services were identified and given indicators that could illustrate the extent of the ecosystem services’ presence. Seven different BGI for stormwater management were studied, to determine which added values they can bring into urban settings. The BGI were green roofs, trees, rain gardens, swales, detention basin, detention ponds and attenuation storage tanks. Nine ecosystem services provided by these BGI were then identified. These were flood protection, water treatment, local climate regulation, air quality control, environmental noise control, erosion prevention, recreation, social relations and biodiversity.  Indicators were identified for each ecosystem service through a literature study. It was noted that to value the ecosystem service, it was not enough to only value the presence of the indicators but also necessary to estimate the demand or need for the ecosystem service. Therefore, questions were formed that could help determine the demand for the ecosystem service. The valuation was then based on how well the presence of the ecosystem service corresponded to the demand of it.  After using this valuation method on a case study, it was concluded that this type of valuation is useful for reconstruction projects in an early stage, to illustrate what functions and demands that need to be considered to obtain more ecosystem services. It can then be used for comparison of different proposals, to see which one provides the most ecosystem services. The valuation is conceptual rather than specific. It is useful as it can include any type of ecosystem service but lacks the perspective of costs.