Documentary evidence of past floods in Europe and their utility in flood frequency estimation

International audienceThis review outlines the use of documentary evidence of historical flood events in contemporary flood frequency estimation in European countries. The study shows that despite widespread consensus in the scientific literature on the utility of documentary evidence, the actual migration from academic to practical application has been limited. A detailed review of flood frequency estimation guidelines from different countries showed that the value of historical data is generally recognised, but practical methods for systematic and routine inclusion of this type of data into risk analysis are in most cases not available. Studies of historical events were identified in most countries, and good examples of national databases attempting to collate the available information were identified. The conclusion is that there is considerable potential for improving the reliability of the current flood risk assessments by harvesting the valuable information on past extreme events contained in the historical data sets.Cet article présente une revue de l'utilisation de l'information documentaire sur les crues historiques par les pays européens pour l'analyse fréquentielle des crues. L'étude montre que, malgré l'existence d'un consensus scientifique sur l'intérêt de ce type d'information, son utilisation reste encore limitée d'un point de vue opérationnel. Si les guides pratiques sur l'estimation des crues mentionnent en général bien l'intérêt de l'information historique, il existe encore peu de logiciel disponible utilisant cette information. Des travaux sont en cours dans plusieurs pays pour constituer des bases de données nationales sur les crues historiques. La conclusion est qu'il y aurait un fort bénéfice à exploiter ces informations pour l'estimation du risque de crue

Changing climate shifts timing of European floods

A warming climate is expected to have an impact on the magnitude and timing of river floods; however, no consistent large-scale climate change signal in observed flood magnitudes has been identified so far. We analyzed the timing of river floods in Europe over the past five decades, using a pan-European database from 4262 observational hydrometric stations, and found clear patterns of change in flood timing. Warmer temperatures have led to earlier spring snowmelt floods throughout northeastern Europe; delayed winter storms associated with polar warming have led to later winter floods around the North Sea and some sectors of the Mediterranean coast; and earlier soil moisture maxima have led to earlier winter floods in western Europe. Our results highlight the existence of a clear climate signal in flood observations at the continental scale