Environment: Extreme flooding and drought make risk management difficult

Risk management strategies for floods and droughts may not reduce the effects of unprecedented events, a paper in Nature suggests. The findings highlight the difficulty of managing such extreme events, which are likely to increase as a result of climate change.

Risk management strategies have reduced global vulnerability to floods and droughts, but the effects of such events are still severe and increasing in many parts of the world. Forecasts for 2 °C of warming suggest that the economic impacts of floods may double globally, and in Europe the economic impact of droughts could triple. Understanding why changes in impact occur is important, but this has been hindered by a lack of empirical data.

Heidi Kreibich and colleagues analysed a dataset of 45 pairs of flood or drought events that occurred in the same area at different time points (16 years apart on average) to assess the effects of risk management strategies. They show that, in general, risk management reduced the impact of floods and droughts; however, when the events were of magnitudes not previously experienced, their effects might not be lessened regardless of the risk management approaches taken. The authors suggest that this outcome may be due to thresholds of infrastructure designed to manage the hazard, such as levees or water reservoirs, being exceeded. The authors also suggest that flaws in human risk perception, especially for rare extreme events, might affect efforts to anticipate them and lessen their effects.

There were two pairs of events (flooding in Barcelona in 1995 and 2018 and Danube catchment floods in Austria and Germany in 2002 and 2013) for which the second event was more hazardous, but the effects were less than those of the first event. Kreibich and colleagues suggest that this was due to improved risk management and investment in integrated management approaches, which led to improved early warning and emergency responses, complemented by structural changes such as levees. The authors conclude that these successful responses could be used to identify risk management strategies to reduce the effects of unprecedented events, which may increase because of climate change.