Coping with Hydrological Extremes

Abstract Coping with hydrological extremes, floods, and droughts has been a major concern since the dawn of human civilization. Freshwater, a necessary condition of life and a raw material used in very high volumes in virtually every human activity, is becoming increasingly scarce. Water use has risen considerably in the last hundred years at a pace exceeding the population growth. Therefore, societies are increasingly vulnerable to droughts and water deficits. Although the 21st century is heralded as the age of water scarcity, flood losses continue to grow. Increasing global vulnerability results to a large extent from soaring anthropopressure: settlements in hazardous locations and adverse land use changes. Deforestation and urbanization lead to reduction of the storage volume and higher values of runoff coefficient. In more wealthy countries, it is the material flood losses that continue to grow, while the number of fatalities goes down. Advanced flood preparedness systems can save lives and reduce human suffering. In some regions of the world, long-term forecasts (e.g., ENSO) help improve the preparedness for hydrological extremes, both floods and droughts, and hopefully will even more so in the future. Scenarios for future climate indicate the possibility of sharpening the extremes and changes of their seasonality. For instance, in Western Scotland and Norway, an increase of winter floods has already been observed. According to recent assessments, there is a growing risk of summer droughts in the Mediterranean region: less precipitation in summer and higher temperature will coincide, causing higher evapo-transpiration and less runoff. Fighting with floods and droughts has not been quite successful. Humans have to get used to the fact that extreme hydrological events are natural phenomena that will continue to occur. While doing one's best to improve the preparedness systems, it is necessary to learn to live with hydrological extremes.