When and where do we reach the limits of adaptation to riverine flood risk?

As climate change and urbanization of low-lying areas increase flood risk, accelerated flood adaptation by households is urgently required (e.g. elevating homes, flood proofing), in addition to adaptation by the government (e.g. dikes) and insurance (cover residual risk). However, there are limits to the adaptability of societies. For instance, social vulnerability factors such as low income or high age may reduce households’ adaptation efforts leading to higher physical vulnerability of their homes. When societies stop implementing additional adaptation, risk may become ‘intolerable’, and people may have no other option than to leave the area. At this point, ‘adaptation limits’ are reached. For the first time, LIMIT2ADAPT will quantitatively assess where and when the limits of flood adaptation are reached given underlaying vulnerability drivers at the global scale. This information is crucial for prioritizing global adaptation fund investments.By pursuing four key outputs, LIMI2ADAPT will assess global risk and the adaptation interactions between households, government and insurers. (1) We will develop a ground-breaking global model for simulating flood adaption limits by integrating two state-of-the-art methods from PIs Bates and Aerts: flood risk- and agent-based models. (2) We will use the new model to simulate historical time series (1km2; 1970-2020) of social and physical vulnerability for four selected river basins, using exposure-, survey- and census data (PIs Tate and Kreibich). (3) We will also simulate global projections (1km2; 2020-2100) of vulnerability(-hotspots) and flood risk. These projections will allow the first spatial-temporal simulation of future adaptation limits at the global scale. Discovering where and when limits occur, and how these are shaped by vulnerability dynamics will lead to (4) a new theory on risk assessment and adaptation limits that sets the scene for future research and policy on climate adaptation.