科研之友
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摘要
During the year 2011, Germany was hit by three transregional hydrological extreme events: a flood in January and two low-flow events in April and November. This article summarizes the results of an extensive study on the causes and characteristics of the two low flow events, which had impacts on waterborne transportation in some rivers. The study is based on climate data from the E-OBS grid product to describe the meteorological situation, and a large number of streamflow records from across Germany as well as over 300 records of groundwater level and spring discharge to characterize hydrological processes. The main objective is to assess the two extreme low flow events and their spatial and temporal characteristics. First, the monthly evolution of streamflow and groundwater in 2011 was analysed across Germany based on anomalies, cumulative departures, and a comparison of 2011 values with the quantiles of the empirical distribution of historic time series. Second, return periods for the low-flow parameter NM21Q (Lowest annual 21-day mean of daily streamflow) were estimated and compared with those of other memorable low-flow years. In addition to the repeated occurrence of extremes in 2011, the most striking characteristic was the unusual seasonal timing of the two low-flow periods in spring and late autumn associated with unusually warm and dry weather over weeks, including the driest November ever. Germany's mountain ranges showed the strongest seasonal anomalies in this respect. A wet period in summer compensated for the spring deficit only in the Northeast of Germany, but deficits were carried over into the autumn event in the watersheds of Rhine, Weser and Danube resulting in similar annual runoff balances as in 2003.
- 出版日期2014-2
