Global mapping of nature based flood risk reduction solutions

Abstract

Coastal flood risk is expected to increase over the 21st century as a result of climate change and economic growth, which makes low-lying regions especially vulnerable. Global screening techniques are needed for a more widespread use of NBS in these flood prone coastal regions. This research expands on the current assessments done by developing a quantitative global screening method that evaluates the costs and benefits for two defence approaches; 1) increasing the dike height, 2) a hybrid solution that includes increasing of the dike height in combination with restoring mangroves and/or corals. The screening method is based on Van Oord’s Climate Risk Overview tool, in which, globally, coastal hotspots are indicated that have a predefined risk of flooding in the 21st century. The steps added by my screening method include; 1) determining which
NBS can be applied depending on the local physical conditions, 2) determining the costs for both NBS and conventional hard solutions, 3) determining the increase/decrease in flood risk of the different interventions for current and future conditions, 4) monetizing additional benefits that NBS provide, 5) assessing the benefits and costs to determine if NBS are the most optimal solution. The results of this global method are inherently limited by several simplifying assumptions and by the lack of high resolution local data, which influences the cost/risk estimates and corresponding site identification. For 2.6-3.3% of the coastal hotspots, NBS can reduce the investment costs in addition to being cost-beneficial. There is potential for expanding this work by adding sea grasses, salt marshes and oyster reefs as vegetated foreshore systems, and by including more thresholds to make the criterion for potential sites to apply NBS more strict.