Are we able to manage severe floods and droughts? In a pair-event study published in Nature, researchers from all over the world have gathered information on flood & drought management for hazardous events. Based on a big data set with detailed information on 45 cases of paired events, we could see that if the second event was much more hazardous than the first, its impact was almost always higher. One would wish that after a first, severe event, the management would lead to improvements that can handle a second hazard in a better way. However, in reality, this is hard to achieve. Our case, Malmö is used as an example in the paper: “… the unprecedented pluvial flood in 2014 in Malmö, Sweden (ID 45) exceeded the capacity of the sewer system and the unprecedented drought in Cape Town (ID 44) exceeded the storage water capacity. This means that infrastructure is effective in preventing damage during events of a previously experienced magnitude but often fails for unprecedented events. Non-structural measures, such as risk-aware land-use planning, precautionary measures and early warning, can help mitigate the consequences of water infrastructure failure in such situations, but a residual risk will always remain. Second, risk management is usually implemented after large floods and droughts, whereas proactive strategies are rare. Part of the reason for this behaviour is a cognitive bias associated with the rarity and uniqueness of extremes, and the nature of human risk perception, which makes people attach a large subjective probability to those events they have personally experienced.” We are, in a different project called GlobalHydroPressure, using this knowledge and are designing decision support indicators that relate for instance water level in a river to the water level experienced during a hazardous flood event in the past. We believe that both early warning systems and urban planning can be made more understandable for both public and decision-makers in this way.

Two success stories were examined in the study in Nature. In these cases, the damage was less, despite a higher hazard, in the second event. Three success factors were identified: effective governance of risk and emergency management, high investment in structural and non-structural measures, and improved early warning and real-time control systems. Read more about the study in Nature.

Article in Nature: Kreibich, H., Van Loon, A.F., Schröter, K. et al. The challenge of unprecedented floods and droughts in risk management. Nature 608, 80–86 (2022). https://doi.org/10.1038/s41586-022-04917-5