Long-term trends in flood discharges of the Ulster and Upper Fulda (Germany): a statistical review

Intensifying processes in the hydrological cycle, induced by global warming, involve the danger of increasing flood discharges. Therefore, in the more recent past several large-scale studies on long-term trends within flood discharge datasets were conducted in Germany. The aim of this work is to supplement the existing findings with a focused, more detailed view on a region within the Central German Uplands as one of the flood generation areas. For this purpose, the catchments of Ulster and Upper Fulda in Eastern Hesse were chosen as study area. Datasets of three gauges, covering the period from 1961 to 2010 as well as datasets of five gauges from 1972 to 2010 were analyzed with statistical methods. Linear trends were calculated, verified and screened for change points. For selected time series, differences in long-term mean maximum discharges before and after these change points were examined with annual, semi-annual and monthly resolution. Results mainly showed upward, but non-significant trends. Most distinctive upward linear trends were detected in time series of the Ulster’s gauges. Change point analysis yielded a characteristic clustering around 1977. The examination of the long-term flood regimes’ dynamics, before and after a harmonized break between 1977 and 1978, revealed higher discharges for the sub-series after 1977, primarily during the winter half year. The results coincide with the findings of large-scale studies for Central, Western and Southern Germany in many ways. In particular long-term flow patterns in contiguous catchments bear a close resemblance to those of the Ulster and Fulda.