Past hydrological events and global change

Information from the period of continuous instrumental observations can provide a context for present processes, and for future scenarios arising from global change. However, much research on periods longer than 100 years has been undertaken by increasingly specialized groups, and there are benefits from bringing their results together. Collaboration by six international groups has collated conclusions and utilized a database of 14C dates from across Europe, providing for the first time a synopsis of Holocene river dynamics in Europe, showing how river basins can respond, through variations in the frequency and magnitude of major floods, more rapidly to climate change than can lake systems. Collaborative research, supported by the International Council for Science (ICSU), allowed the six international research groups (Table I) to combine recent results for periods prior to those of continuous instrumental records by focusing on hydrological events. Research groups relevant to potential global change impacts each operate at a particular time and spatial scale, often with their own particular emphasis; there are some areas of overlap (Figure 1), but it is from their collective results that information can be derived for underrepresented areas. The possibility of more climatic variability, and of changes in the occurrence of particular types of event, such as increased storminess, flood events, blizzards, drought periods, is one subject for multidisciplinary research. Because changes do not occur in a linear, progressive way, and vary from one area to another, information is required from periods longer than those of continuous instrumental records, and from ungauged sites.