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.
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.