Our main conclusion is that Nature based solutions may come with high positive social benefits. Therefore, a well-informed cost benefit analysis should include as well direct costs and damages as positive externalities such as increased biodiversity, water purification, human health, and recreational values. This will help decision makers to conduct well informed decision that maximises societal benefits, and at the same time helping to efficient adapt to climate change.
To make well informed decisions regarding how to tackle a specific problem related to increased sea levels, storm surges, and extreme rain, a cost benefit analysis (CBA) should be included in the process. In this report we have shown that the inclusion of positive externalities from nature-based solutions in the CBA can contribute at such a magnitude that the effect should not be neglected. During this project we realised that the important CBA was not included in all decision processes, and on some occasions, they seem to have been conducted after the decision to justify it, rather than with the purpose to inform the process.
To monetise externalities from the NBS we have used valuation studies of high quality in the benefit transfer. However, the match between the study sites and our analysed policy sites is often not perfect. We therefore see great need for more primary environmental valuation studies of positive externalities of NBS, both in general and particular in the Nordic countries. The externalities in question include both recreational, landscape aesthetic and educational ecosystem services benefits, as well as increased biodiversity and purification of nutrients (nitrogen and phosphorous) and pollutants like microplastics. For an example of the former, see a recent Stated Preference survey of opening a stream as a local NBS in Eastern Norway (Dugstad, Hammou, & Navrud, 2024).
During the process of adapting results from existing surveys to our identified cases, several uncertainties occur. First, the magnitude of the impact or change in the individual ESs (and the baseline from which the change took place) valued from the primary valuation study is different from in our policy case sites. Second, the individuals’ valuation of the impact might not be the same at our policy sites as in the original study, as people’s preferences vary geographically and over time, and our procedure for correcting for this in the benefit transfer might not capture all this variation. In our benefit transfer exercise, we have taken a conservative approach and tried to underestimate rather than overestimate the external benefits of NBS.