Freiburger Schriften zur Hydrologie

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Band/volume 15: STAHL K. (2001):

Hydrological Drought - a Study across Europe

Aiming at a better understanding of drought causes and processes, the present study investigated hydrological drought characteristics in space and time and their large-scale atmospheric driving forces in Europe. On the basis of daily streamflow data of more than 600 European rivers for 1962-1990, two types of events were defined: streamflow drought, defined by a seasonally constant threshold and streamflow deficiency, defined by a new varying threshold level method. By the means of cluster analysis, the 602 streamflow deficiency series across Europe were classified into 19 regions. A regional streamflow deficiency index (RDI) provided a parameter describing how strong a region is affected by streamflow deficiency. This index allowed a first assessment of the space-time characteristics of the major dry spells in Europe in 1962-90. Regions such as Spain, SE-UK, S-Scandinavia and N-Germany show a tendency to persistent dry spells while the index fluctuates more strongly in other regions.
Anomalies of atmospheric circulation patterns (Europäische Großwetterlagen) during severe regional streamflow deficit were analysed. The grouped circulation patterns (CP) provide an adequate input for a new model to predict the regional streamflow deficiency index. Two different applications of the CP-RDI link model were tested:
historic reconstruction and scenario prediction of regional streamflow deficiency indices. The reconstruction since 1881 confirms the trend towards drier conditions in the end of the 20th century in Spain and shows changes towards longer dry spells after the 1960s in some regions. The response to the scenario, which was motivated by changes in circulation patterns attributed to climate change, confirm that Europe will be exposed to generally wetter conditions, however rare and severe drought may increase in some regions.

[ deutsche Zusammenfassung ]

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