The challenge of unprecedented floods and droughts in risk management

Abstract

Risk management has reduced vulnerability to floods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3.

How path dependency manifests in flood risk management: observations from four decades in the Ennstal and Aist catchments in Austria

“…In FRM, specific self-reinforcing mechanisms appear as learning effects and interconnected management that privileges certain kinds of expertise (Parsons et al 2019 ); and as sunk costs of flood defences, high transition costs because of narrow technical expertise, strongly formalised institutions and organisations and the perceived responsibility for FRM at the state level (Wiering et al 2017 ). Adaptive expectations, that is, basing future decisions on the experience of past events assuming that risks will remain as they are, manifest in difficulties to design levees and reservoirs not just to the level of previous but to unprecedented flood events (Kreibich et al 2022 ).…”

Building-scale flood loss estimation through vulnerability pattern characterization: application to an urban flood in Milan, Italy

“…Since the structural vulnerability is defined as the potential of a particular class of buildings or infrastructure facilities to be affected or damaged under a given flood intensity (Faella and Nigro, 2003), damage by flood hazard depends on the vulnerability of exposed buildings (Schanze, 2006;Merz et al, 2010). Vulnerability matrices, depth-damage curves and vulnerability indices (Balica et al, 2009; or indicator-based methodology (Kappes et al, 2012) are methods and approaches mainly used for physical vulnerability assessment (Fuchs et al, 2019;Kumar and Bhattacharjya, 2020;Malgwi et al, 2020). The indicator-based methods usually provide a scale of flood vulnerability to elements at risk, having the strength of allowing significant factors that contribute to flood vulnerability to be understood easily by potential users.…”

“…This makes measurement of progress in reducing the disaster risk difficult if not infeasible. Therefore, some authors stressed the need for the use of empirical data from past events to provide powerful analytical tools (Apel et al, 2008;Vamvatsikos et al, 2010;Kreibich et al, 2022). The ideal solution would be a model that is simple, as the empirical ones, but that includes quantitative and qualitative explicative parameters in damage assessment, as the synthetic ones, to capture the full complexity of buildings vulnerability (Schanze, 2006;Balica et al, 2009;Lal et al, 2012;Morelli et al, 2021).…”

“…Here vulnerability assesses the susceptibility to harm of exposed residential buildings when exposed to the hazard (USACE, 2019;Kreibich et al, 2022) to (1) address the necessity of an integrated qualitative and quantitative approach to define flood physical (structural) vulnerability; (2) to accurately re-assess past event flood characteristics; (3) to bridge the gap of vulnerability spatialization using spatially distributed information to obtain vulnerability mapping and related potential damage suitable for giving indications on where and how to reduce risks at local level; (4) to bridge the lack of reliable input data in particular regarding the properties of the elements at risk (i.e. the exposure and susceptibility factors) that also contribute to their vulnerability at building level; and (5) to improve the exposure analysis integrating the building's surroundings as a vulnerability indicator (i.e.…”

Detectable Increase in Global Land Areas Susceptible to Precipitation Reversals Under the RCP8.5 Scenario

“…Floods are associated with extremes in rainfall, whereas drought is a protracted period of deficient precipitation (Trenberth, 2005). Rapid transition from one end of precipitation spectrum to the other, for example, from droughts to floods or vice versa can be associated with larger socio‐economic impacts than each individual type of the events, in particular, if the second event was much more hazardous than the first (Kreibich et al., 2022). There are myriad examples in this regard.…”