Uncertainty and Bias in Global to Regional Scale Assessments of Current and Future Coastal Flood Risk

This study provides a literature-based comparative assessment of uncertainties and biases in global to world-regional scale assessments of current and future coastal flood risks, considering mean and extreme sea-level hazards, the propagation of these into the floodplain, people and coastal assets exposed, and their vulnerability. Globally, by far the largest bias is introduced by not considering human adaptation, which can lead to an overestimation of coastal flood risk in 2100 by up to factor 1300. But even when considering adaptation, uncertainties in how coastal societies will adapt to sea-level rise dominate with a factor of up to 27 all other uncertainties. Other large uncertainties that have been quantified globally are associated with socio-economic development (factors 2.3–5.8), digital elevation data (factors 1.2–3.8), ice sheet models (factor 1.6–3.8) and greenhouse gas emissions (factors 1.6–2.1). Local uncertainties that stand out but have not been quantified globally, relate to depth-damage functions, defense failure mechanisms, surge and wave heights in areas affected by tropical cyclones (in particular for large return periods), as well as nearshore interactions between mean sea-levels, storm surges, tides and waves. Advancing the state-of-the-art requires analyzing and reporting more comprehensively on underlying uncertainties, including those in data, methods and adaptation scenarios. Epistemic uncertainties in digital elevation, coastal protection levels and depth-damage functions would be best reduced through open community-based efforts, in which many scholars work together in collecting and validating these data.DL, GLC, JH, MM, RvdW have been partially supported by the ERA4CS Project INSeaPTION (grant 01LS1703A) and DL and JH by the Project ISIPEDIA (grant 01LS1711C). Both Projects are part of ERA4CS, an ERA-NET initiated by JPI Climate and funded by FORMAS (SE), BMBF (DE), BMWFW (AT), IFD (DK), MINECO (ES), ANR (FR) with co-funding by the European Union (Grant 690462). DL, JH, RN and RvdW have received funding from the PROTECT project (grant 869304), and DL and JH from the COACCH project (grant 776479), both funded under the European Union's Horizon 2020 Research and Innovation Programme. ATV, CW, DL and JH have been supported by the Deutsche Forschungsgemeinschaft (DFG) through the SEASCAPE II project, which is part of the Special Priority Program 1889 Regional Sea Level Change and Society. MM has been partially supported by the MOCCA project (grant RTI2018-093941-B-C31). TW was partially supported by the National Aeronautics and Space Administration (NASA) under the New (Early Career) Investigator Program in Earth Science (grant number: 80NSSC18K0743) and MH was partially supported by the Australian Government National Environmental Science Program Earth Systems and Climate Change Hub. PJW has been supported by the Dutch Research Council (NWO) in the form of a VIDI grant (grant no. 016.161.324)