NbS Triple Win Toolkit: Economics and Finance 77 2. Avoided cost methods typically generate larger benefit-cost ratios. NbS which protect (often coastal) economic assetsor prevent degradation (and further carbon emissions) may deliver benefits earlier in the project lifecycle than other NbS which require the restoration of ecosystems over longer timeframes. The extent to which this impacts the benefit-cost ratio will depend on the price of carbon used in the project appraisal118, as well as the levelof assumptions underpinning any avoid cost calculations. From an economic perspective, the discount rate is particularly important because of the timing profile of benefits and cost. Evidence from the case studies suggests that many NbS projects have high upfront costs in the early years of a project, proportionally lower maintenance costs in later years, and generate benefits over a long period of time. Since cost-benefit and cost-effectiveness analyses weight the benefits and costs more heavily in early years in comparison with later years, high up-front costs, or high up-front benefits in the case of avoided cost approaches, are attributed greater economic importance. Whilst the Green Book has specific guidance on the discount rate to be used for UK projects, and a consultation is out in 2021 refining specific guidance around the discount rate in respect of projects with impact on the environment, it is of particular importance that the impact of the discount rate is well understood for each individual project. Sensitivity analysis of prospective projects and post-project assessments can illuminate the impact of the discount rate, as well as which benefits and costs are most likely to be impacted. 3. Most of the benefit-cost ratios are below 10 and have a focus on improvements in local livelihoods. The focus of valuation for most NbS projects in on quantifying additional income for local communities, whereas the global studies look predominatelyat avoided damages and the benefits of carbon mitigation. It is challenging to compare the economic impact of NbS on local revenue-generating impacts due to the distinct local economic conditions of each location. Similarly, alternative approaches and interventions proposed to achieve the same strategic objectives are not available to analyse, making it difficult to understand the NbS investment case in comparison with other rejected proposals. The economic and strategic case for NbS is likely to be understated if the full suite of benefits and costs are not integrated into the economic assessment. This is particularly relevant for qualitative non-market benefits such as biodiversity and social benefits which are difficultto define but are significant considerations for local communitiesand important strategic objectives of UK Government. In addition, benefits selected for assessment under the triple win headlines may differ significantly in spatial scale, from addressing global trends to adapting to local conditions. The economic case for investment in a given region or ecosystem may be driven by the high social cost of carbon emissions, but this does not immediately translate into either local financial or social benefits even if local communities benefit from reducing carbon emissions. This is particularly the case where NbS projects targeting climate change mitigation (e.g. reforestation) require the cessation of activities which are essentialfor local livelihoods but degrade local ecosystems. It does not consider the reality for local communities of NbS projects on a landscape scale nor feasibility of mechanisms (i.e. carbon credits or payments for ecosystem services) which may be required to adapt to such changes. To facilitate study comparisons, especially from the perspectiveof the triple win, it is as important to document and evaluatethe benefits which have not been quantified in an economic assessment as it is for those which are valued. Techniquessuch as cost-benefit analyses make it challenging to standardiseand give parity to the qualitative benefits which NbS can deliver.