Analyses of seasonal and annual maximum daily discharge records for central Europe

Annual and seasonal maximum daily discharge time series for 55 stations in central Europe (Germany, Switzerland, Czech Republic, and Slovakia) are used to examine flood frequency from a regional perspective. In this study we examine temporal nonstationarities in the flood peak records, and characterize upper tail and scaling properties of the flood peak distributions. There is a marked seasonality in the flood peak record, with a large fraction of annual maximum flood peaks occurring during the winter in the western part of the study domain, and during the summer in the southern portion of this region. The presence of abrupt and slowly varying changes in the flood time series is examined by means of non-parametric tests. Change-points in the mean and variance of the flood peak distributions are examined using the Pettitt test, while the presence of monotonic patterns is examined by means of Spearman and Mann-Kendall tests. Abrupt changes, rather than monotonic trends are responsible for violations of the stationarity assumption. These step changes can often be associated with anthropogenic effects, such as construction of dams and reservoirs and river training. Given the profound changes that these catchments have undergone, it is difficult to detect a possible climate change signal in the flood peak record. The estimates of the location, scale, and shape parameters of the Generalized Extreme Value distribution are used to examine the upper tail and scaling properties of the flood peak distributions. The location and scale parameters exhibit a power law behaviour when plotted as a function of drainage area, while the shape parameter decreases log-linearly for increasing catchment area. The findings of this study suggest that these records exhibit a heavy tail behaviour.