Graduation of Tjerk Krijger

 Global mapping of nature based flood risk reduction solutions

• Professor of graduation: Prof. dr. ir. S.N. (Bas) Jonkman

• Supervisors: Prof. dr. ir. S.G.J. (Stefan) Aarninkhof (TU Delft), Ir. A.G.M. (Alejandra) Gijón Mancheño (TU Delft), Dr. ir. Gerben J. de Boer (Van Oord)

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. In order to promote and increase more widespread use of nature-based solutions (NBS) in flood prone coastal regions, global screening techniques are required. This research expands on the current assessments done by developing a quantitative global screening method that evaluates the costs and benefits for two defense approaches; 1) the traditional dike protection, 2) a hybrid solution including a dike in combination with NBS such as 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 of the 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) monetize additional benefits that NBS provide, 5) assess the benefits and costs. Out of the identified potential NBS sites, it is found that 10-26% would be more economical than having only dikes (lower investment costs). For 4.5-5.5% of the potential NBS sites next to lower investment costs also the flood risk reduction benefits are found to outweigh the investment costs (dike and restoration costs). The results of this method are limited by several simplifying assumptions and by the lack of high resolution data, which influences the cost estimates and site identification. Developing systematic methodologies for identifying potential sites for NBS provides more insight into the economical benefits they yield. Combining the additional benefits of these ecosystems with their flood risk reduction, results in more resilient and sustainable protection methods against SLR.