The challenges of unprecedented floods and droughts in risk management.

Abstract

Risk management has reduced vulnerability to foods and droughts globally, yet their impacts are still increasing. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data. 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 foods and droughts but faces difculties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the frst, 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 difculty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change. .