10 Hydrological Impacts of Climate Changes in Romania
321
trends (at 95% confidence level) in winter, spring, autumn and at annual time scale
over the northwestern part of the country and decreasing trends (at 95% confidence
level) in spring over the southern part of the country.
As for the Lower Danube River (on the Romanian territory), it was found by
Mikhailova et al. [145] that during 1840–2000, at the entrance to its delta, there were
no significant changes in mean annual discharges, but a slightly decreasing trend
was identified after 1970. A decreasing trend in mean annual discharges was also
noticed after 1975 in [146]. A similar negative trend in the annual mean discharges
of the Danube River at the entrance to the delta (at Ceatal Izmail or Ceatal Chilia)
was identified during 1948–2004 in [32] and was explained by the global warming,
as well as by changes due to human activities (e.g., withdrawal of stream water for
different uses, dams and reservoirs).
Between 1931 and 2010, according to [147], the annual average discharge of the
Danube River had a slightly decreasing trend at its entry in Romania (at Bazias , g.s.).
Meanwhile, at the entrance to the delta, at Ceatal Izmail/Chilia, a slight increasing
trend was found, in contradiction to previous studies mentioned above (the divergence
could be due to differences in the analyzed periods; additionally, the linear trends with
a low slope were visually established without being statistically tested). During the
analyzed period (1931–2010), the minimum annual discharges of the Danube River
had upward trends at the entry in Romania, as well as at the entrance to the delta,
more obvious after 1985. Concerning the maximum annual discharges, at Bazia¸ s, no
trend was detected, while at Ceatal Izmail/Chilia, a slight upward trend was found
especially after 1990 [147].
During 1930–2008, shifts in seasonal discharge of the Danube River at the entrance
to its delta (at Ceatal Izmail/Chilia) were identified. Thereby, after 1991 the presentday spring high flows and floods tend to occur earlier, the summer runoff is diminished
and the low flows in autumn are slightly higher (in October–November) compared
to those of the early 20th century [85].
The alterations in annual flow and regime of the Danube River on Romanian territory can be attributed to climate variability/changes, water management activities, as
well as land use change. Since 1970, the reservoir dam of Iron Gates I, located at the
entrance of the river in Romania (Fig. 10.1), had a major influence on the streamflow
and sediment load of the Lower Danube River. The dam caused alterations of the
natural annual flow regime due to its regularization role. Thus, during low water
periods, the discharges increase (in winter and autumn), while during high waters (in
spring and early summer) they are reduced in order to mitigate the flood magnitude
[148].
At the regional/watershed scale, the identified trends in streamflow are heterogeneous, being influenced by local climate changes (in the lack of major anthropic
pressures). In the Carpathian Curvature region, during 1962–2006, no significant
trends were found in the annual flood peak variability and the number of floods
exceeding the attention stage (corresponding to the yellow warning code) [137].
Similar results were found in the eastern Carpathians, in the Trotus , River catchment
[138]. In the Southern Carpathians (more precisely, in the Bucegi Mountains), a significant upward trend in the magnitude of annual floods was identified between 1961
321
trends (at 95% confidence level) in winter, spring, autumn and at annual time scale
over the northwestern part of the country and decreasing trends (at 95% confidence
level) in spring over the southern part of the country.
As for the Lower Danube River (on the Romanian territory), it was found by
Mikhailova et al. [145] that during 1840–2000, at the entrance to its delta, there were
no significant changes in mean annual discharges, but a slightly decreasing trend
was identified after 1970. A decreasing trend in mean annual discharges was also
noticed after 1975 in [146]. A similar negative trend in the annual mean discharges
of the Danube River at the entrance to the delta (at Ceatal Izmail or Ceatal Chilia)
was identified during 1948–2004 in [32] and was explained by the global warming,
as well as by changes due to human activities (e.g., withdrawal of stream water for
different uses, dams and reservoirs).
Between 1931 and 2010, according to [147], the annual average discharge of the
Danube River had a slightly decreasing trend at its entry in Romania (at Bazias , g.s.).
Meanwhile, at the entrance to the delta, at Ceatal Izmail/Chilia, a slight increasing
trend was found, in contradiction to previous studies mentioned above (the divergence
could be due to differences in the analyzed periods; additionally, the linear trends with
a low slope were visually established without being statistically tested). During the
analyzed period (1931–2010), the minimum annual discharges of the Danube River
had upward trends at the entry in Romania, as well as at the entrance to the delta,
more obvious after 1985. Concerning the maximum annual discharges, at Bazia¸ s, no
trend was detected, while at Ceatal Izmail/Chilia, a slight upward trend was found
especially after 1990 [147].
During 1930–2008, shifts in seasonal discharge of the Danube River at the entrance
to its delta (at Ceatal Izmail/Chilia) were identified. Thereby, after 1991 the presentday spring high flows and floods tend to occur earlier, the summer runoff is diminished
and the low flows in autumn are slightly higher (in October–November) compared
to those of the early 20th century [85].
The alterations in annual flow and regime of the Danube River on Romanian territory can be attributed to climate variability/changes, water management activities, as
well as land use change. Since 1970, the reservoir dam of Iron Gates I, located at the
entrance of the river in Romania (Fig. 10.1), had a major influence on the streamflow
and sediment load of the Lower Danube River. The dam caused alterations of the
natural annual flow regime due to its regularization role. Thus, during low water
periods, the discharges increase (in winter and autumn), while during high waters (in
spring and early summer) they are reduced in order to mitigate the flood magnitude
[148].
At the regional/watershed scale, the identified trends in streamflow are heterogeneous, being influenced by local climate changes (in the lack of major anthropic
pressures). In the Carpathian Curvature region, during 1962–2006, no significant
trends were found in the annual flood peak variability and the number of floods
exceeding the attention stage (corresponding to the yellow warning code) [137].
Similar results were found in the eastern Carpathians, in the Trotus , River catchment
[138]. In the Southern Carpathians (more precisely, in the Bucegi Mountains), a significant upward trend in the magnitude of annual floods was identified between 1961