How often do extreme events occur?

The estimation of return periods of extreme events can be improved by combining historical data, rainfall-runoff modelling and flood frequency analysis. Discharge records can often be extended using historic events. A better understanding of the relevant runoff formation processes helps to assess the magnitude of extreme floods. To this purpose, plots of 60 m(2) with different soils and geology were exposed to artificial rains of up to 100 mm h(-1) for several hours and relevant flows monitored. Based on these results, maps of areas with different reactions to precipitation were developed and used for runoff computations. Examples of combined analyses of historic events, flood frequency analysis and simulations with a model based on plots are presented.