Time variable effectiveness and cost-benefits of different nature-based solution types and design for drought and flood management

Abstract

Nature Based Solutions (NBS) for water resources management have potential to mitigate climate change impacts, including more frequent flooding and droughts. Successful uptake requires more knowledge on the effects of NBS type and design on high and low flows. The cost-benefits of NBS impacts on these and water yield are also essential. Here, we used a modelling framework to explore the impacts of two common NBS types (Runoff Attenuation Features [RAFs] and tree planting), both varying in design, specifically location and scale. Data from an upland Scottish catchment (∼1km2) informed a coupled physically-based hydrological (MIKE SHE) and hydraulic (MIKE 11) modelling approach. NBS scenario effects on high and low flows, as well as groundwater recharge were compared and hydrological indices specific to the whisky industry informed the study site's 25-year cost-benefit analysis. Overall, tree planting reduced low flows and recharge of groundwater, whereas RAFs had a positive but smaller effect. Both NBS types reduced high and medium flows, although tree planting reduced high flows less than RAFs. RAF design, particularly increases in storage volume spread over greater areas, increased effects on all aspects of flows and recharge. Greater areas of planting increased effects on all but the highest flows. NBS type and design affected timing of water storage availability, retention and transfer, but this also depended on antecedent wetness, so these should all be considered for optimal performance or avoiding negative effects. The cost-benefit analysis revealed that RAFs would be a financially feasible NBS approach for enhancing low flows, whereas tree planting would not. This study highlighted that implementing a modelling framework alongside cost-benefit analysis could help optimise type and design of NBS for cost-effective management of specific local water availability issues. Critically this could inform NBS implementation for management of flood and drought impacts, likely to become more frequent in future with climate change.