extreme hydrological events on the lower danube ... - sh.fgg.uni-lj.si

EXTREME HYDROLOGICAL EVENTS ON THE LOWER DANUBE
AND IN THE MOUTH AREA DURING RECENT DECADES
Maria Mikhailova 1 , Victor Morozov 2 , Nataliya Cheroy 2
1 Water Problems Institute, Russian Academy of Sciences
Moscow, Russia
2 Danube Hydrometeorological Observatory
Izmail, Ukraine
mv.mikhailova@gmail.com, morozov@izm.odesa.ukrtel.net, nataly_cheroy@mail.ru
Abstract
The formation and transformation of the <strong>extreme</strong> rainfall flood in August 2002,
spring–summer flood in March–June 2006, and water levels during low water period
in August–October 2003, and the preceding meteorological situation were studied.
During catastrophic rainfall and spring–summer floods, at some gauging stations the
levels exceeded historical marks and caused inundations. In autumn 2003, water
levels in the Lower Danube reached minimum-recorded values and affected
agriculture, water supply, navigation, etc.
Keywords: <strong>extreme</strong> <strong>hydrological</strong> <strong>events</strong>, rainfall flood, spring and summer flood, low
water period, drought, inundation.
1 INTRODUCTION
Late in the 20th century and early in the 21st century, a frequency of catastrophic
<strong>hydrological</strong> <strong>events</strong> on the Danube River increased. In the Danube River basin and in
the basins of the other European rivers (Elbe River in Germany, Kuban’ and Terek
rivers in Russia, etc), <strong>extreme</strong> <strong>hydrological</strong> <strong>events</strong> happened over the latest years,
are evidence of new tendencies in the meteorological and <strong>hydrological</strong> processes.
Global climate warming, intensification of synoptic processes, increment in the total
amount of precipitation and its irregularity resulted in an increase in a frequency of
<strong>extreme</strong> <strong>hydrological</strong> <strong>events</strong>.
In a frame of our investigations, we consider: formation and transformation of the
Danube catastrophic rainfall flood in August 2002, when the flood peak spread from
the river source to the Iron Gate reservoir in 15 days, and at a number of gauging
stations on the Middle and Lower Danube the levels exceeded historical maxima and
caused a catastrophic inundation; formation of the <strong>extreme</strong> spring–summer flood in
March–June 2006, when water levels on the Lower Danube also exceeded historical
maxima; peculiarities of the <strong>extreme</strong> low water period (drought) in August–October
2003, when water levels on the Lower Danube were the lowest since 1950.
In our study, we use the results of join Russian and Ukrainian investigations of the
regime of the Lower Danube and its delta, and <strong>hydrological</strong> and meteorological
observational data of Danube Hydrometeorological Observatory (Izmail). Long-term
trends in changes in many hydrometeorological characteristics were revealed. During
recent decades, the air and water temperature, the amount of precipitation increased.

2 RAINFALL FLOOD IN AUGUST 2002
2.1 Synoptic situation preceding the flood
Severe squalls, downpours, and the flood in the first half of August 2002 were due to
the intensification of the meridional atmospheric processes, which induced conditions
favorable for the intrusion of the cold Arctic air far to Southern Europe.
The flood in Western and Central Europe was caused by the following factors: the
unusually intense cold air outbreaks in south of Western Europe; cyclogenesis
intensification and formation of upper level cyclones with cold centers; intense
cyclonic activity at the polar front, where very warm Atlantic tropical air interacted
with cold Arctic air masses; convective instability and large-scale ordered ascending
motions at the atmospheric front. All these factors produced violent squalls and rains,
with а precipitation depth well above normal. There were avalanches in Europe's
mountainous regions. In the first half of August, а rain belt covered the southern and
eastern parts of Germany and Austria, Czechia, Slovakia, and adjacent territories.
On the upper Danube and upper Elbe, particularly heavy rains occurred on 6–7 and
11–12 August. The first portion of rains caused floods on rivers in Germany (Saxony
and Bavaria) and in the southern and western parts of Czechia. When the second
wave of rains came, soil had already been water-saturated and water levels in the
rivers had already been high. Therefore, the water levels on all the rivers rose
rapidly, occasionally reaching а historical maximum.
2.2 Development and transformation of the Danube rainfall flood
When analyzing the formation and movement of the August 2002 flood, daily water
levels from <strong>hydrological</strong> gauging stations located throughout the length of the
Danube River from its upper reach to the mouth were used as the initial information
(Figure 1 and Table 1). The data were obtained by the Danube Hydrometeorological
Observatory (DHMO) through in international exchange of <strong>hydrological</strong> data. Water
levels measured daily at 08:00 GMT were used to construct the plots (Figure 2)
which showed the evolution of the flood from the Danube River source to its mouth.
To compare the water levels measured in August 2002 with the historical maximum
levels, the data of the DНМО and reference data on Danube hydrology were used
(Hydrology…, 1963; Die Donau…, 1986; Hydrology…, 2004; Mikhailov et al., 2004).
The very first flood wave on the Upper Danube (from the river source to the
confluence with the Morava) began to form approximately on 6 August. The first flood
peak at the gauging stations of Ingolstadt, Regensburg, Passau, Linz, Kienstock, and
Bratislava occurred on 8–9 August. А second flood wave began to form after 11
August. Since heavy precipitation simultaneously fell across the Upper Danube basin
and its tributaries, the peak of the second flood wave between Ingolstadt and
Kienstock (80 km above Vienna) occurred almost simultaneously, on 13–15 August.
Only below Kienstock the flood took the form of а strong wave moving downstream.
А new flood peak occurred at the German gauging stations of the Danube River
(Ingolstadt, Regensburg, and Passau) on 14, 15, and 13 August, respectively.

Figure 1. Danube River basin and location of gauging stations. 1–29 – gauging
stations in accordance with Table 1 and 2.
At the upper boundary of the Middle Danube, the water level near Bratislava was
rising rapidly, beginning on 12 August. The maximum water level at Bratislava was
measured on 16 August. It reached 986 cm above gauging station zero and
exceeded the historical maximum of July 1954 by 2 cm. The flood wave peak
covered the distance between Kienstock and Bratislava (146 km) in 2 days, moving
at a rate of 73 km/day, or 0.84 m/s
At Budapest, the water level began to rise approximately on 8 August (Figure 2). The
second flood wave covered the distance between Bratislava and Budapest (222 km)
in 3 days (it moved at а rate of 74 km/day, or 0.86 m/s). In Budapest, а lowland area
of the Pest district located on the left bank of the Danube was damaged.
Embankments near the Parliament Building and subways were submerged, some
other buildings were destroyed. The flood peaked on 19 August. The level rose to
844 cm above gauging station zero. It was only 1 cm lower than the historical
maximum and about 630 cm higher than the early August mean level. By 21 August,
the flood wave reached Baja, and by 22 August, it reached Mohacs (at the boundary
between Hungary and Croatia). The distance from Budapest to Mohacs (200 km)
was covered in 3 days at а rate of 66.7 km/day, or 0.77 m/s.
In Croatia, the maximum levels were recorded at Bezdan on 22 August and Bogojevo
on 23 August; they were 712 and 727 cm above gauging station zero, exceeding the
early August mean level by almost 600 cm. From Mohacs to Novi Sad in Serbia (192
km), the flood wave came in 3 days, moving at а rate of 64 km/day, or 0.74 m/s, and
from Novi Sad to Zemun (82 km), in 2 days at а rate of 41 km/day, or 0.47 m/s. The
maximum levels were recorded on 25 and 27 August, respectively. At Вazias,
Romania, the flood peak occurred on 28 August. Thus, on the Middle Danube (from
Bratislava to the Iron Gate reservoir), the flood wave spread in about 12 days.

Table 1.Maximum rain flood levels, August–September 2002, and historical maximum levels at gauging stations on the Danube
River. Dash means lack of information.
№ Gauging
station
Country
Distance from
the Black Sea
(port of Sulina)
(km)
Maximum level
above gauging
station zero (cm)
Rain flood in August 2002
Date
Height of rise
above the preflood
level (cm)
Historical maximum (in ice-free period)
Period Level Date
(cm)
1 Ingolstadt Germany 2458 642 14.08 390 1827–1970 778 18.06.1910
2 Regensburg Germany 2376 627 15.08 280 1884–2001 666 28.03.1988
3 Passau Germany 2225 1083 13.08 550 1877–2001 1230 10.07.1954
4 Linz Austria 2135 799 13.08 420 1893–2001 963 11.07.1954
5 Kienstock Austria 2015 1085 14.08 780 1830-2001 896 13.07.1954
6 Bratislava Slovakia 1869 986 16.08 650 1823–2001 984 15.07.1954
7 Nagymaros Hungary 1695 707 18.08 600 1876–2001 682 17.06.1965
8 Budapest Hungary 1647 844 19.08 630 1876-2001 845 17.06.1965
9 Mohach Hungary 1447 924 22.08 650 1876–2001 984 19.06.1965
10 Bezdan Croatia 1425 712 22.08 600 1876–2001 776 24.06.1965
11 Bogojevo Croatia 1367 727 23.08 600 1890–2001 817 15.06.1965
12 Novi Sad Serbia 1255 602 25.08 460 1888-2001 778 30.06.1965
13 Zemun Serbia 1173 470 27.08 240 1876–2001 757 26.03.1981
14 Bazias Romania 1072 628 28.08 50 1874–1970 795 06.04.1942
15 Orsova Romania 955 2540 01.08 – 1888–2001 2568 17.10.1994
16 Turnu-Severin Romania 931 831 27.08 150 1879–2001 906 28.03.1981
17 Novo Selo Bulgaria 834 513 28.08 360 1941–2001 900 28.03.1981
18 Calafat Romania 795 415 22,28.08 360 1879–2001 801 29.03.1981
19 Lom Bulgaria 743 558 28–29.08 360 1921–2001 934 29.03.1981
20 Zimnicea Romania 554 411 30.08 310 1879–2001 800 02.06.1970
21 Giurgiu Romania 493 376 24,30.08 320 1879–2001 795 02.03.1970
22 Olenita Romania 430 393 31.08 320 1879–2001 784 1897
23 Hirsova Romania 253 413 02–03.09 320 1898–2001 727 04–06.06.1970
24 Braila Romania 170 431 02–03.09 270 1874–2001 639 28.05.1970
25 Reni Ukraine 127 350 2.09 220 1921–2001 555 28.05.1970

1100
900
1000
900
800
700
Н, cm
Bratislava
800
700
600
Н, cm
Budapest
600
500
500
400
300
200
100
400
300
200
100
0
0
1.8
5.8
9.8
13.8
17.8
21.8
25.8
29.8
2.9
6.9
10.9
1.8
5.8
9.8
13.8
17.8
21.8
25.8
29.8
2.9
6.9
10.9
700
600
500
400
300
200
100
0
2600
Н, cm Novi Sad
Н, cm
Orsova
2500
2400
2300
2200
1.8
5.8
9.8
13.8
17.8
21.8
25.8
29.8
2.9
6.9
10.9
1.8
5.8
9.8
13.8
17.8
21.8
25.8
29.8
2.9
6.9
10.9
500
400
400
Н, cm
Calafat
300
Н, cm
300
200
100
200
100
Reni
0
0
1.8
5.8
9.8
13.8
17.8
21.8
25.8
29.8
2.9
6.9
10.9
1.8
5.8
9.8
13.8
17.8
21.8
25.8
29.8
2.9
6.9
10.9
Figure 2. Level variations at some gauging stations on the Danube River, August–
September 2002
On the Lower Danube, the water level rise started on 9 August, when the water was
released from the Iron Gate I and II reservoirs at the boundary between Serbia and
Romania. The removal was made in advance to accumulate the flood water and, if
possible, to decrease the flood downstream of the reservoir. In the period from 9 to
16 August, the water level at the head of the reservoir was lowered by 90 cm, and in
the period from 17 to 22 August, by another 170 cm. When the flood reached the Iron
Gate (26–27 August), the level in the reservoir was lowered by 260 cm. This made it
possible to accumulate the bulk of the flood water in the reservoir and to prevent а
further level rise on the Lower Danube.

On the Lower Danube (from Turnu-Severin to the sea), there was not а flood but an
artificial release of water from the Iron Gate I (the dam site is 943 km from the Black
Sea) and Iron Gate II (863 km from the Black Sea) reservoirs. А comparison of the
level changes at Novi Sad and Оrsova (at the head of the reservoir) (Figure 1) clearly
demonstrates how the timely water removal from the reservoir "smoothed out" the
rainfall flood. While at Novi Sad the maximum level was recorded on 25 August and
at Zimnicea and Bazias the maximum was measured on 27 and 28 August, а
minimum level occurred at Orsova on 22 August.
On the Romanian reach of the Danube at Calafat, the level began rising on 9 August
(when the water was released from the reservoir) (Figure 2). By 22 August, the water
level had reached а maximum (415 cm above gauging station zero) and exceeded
the mean level before the release of water by 360 cm. Then it lowered by 20 cm and
reached а maximum again on 28 August. At Zimnicea, Giurgiu, and Oltenita, the
level varied in а similar way. At the first two points, it began rising on 9 August,
reaching а maximum of 411 and 376 cm, respectively, on 30 August. At Oltenita, the
maximum level was recorded on 31 August (393 cm above gauging station zero).
The maximum levels at these three gauging stations exceeded the mean levels
before the release of water by 310, 320, and 320 cm, respectively. At the Romanian
gauging stations of Hirsova and Braila and at the Ukrainian gauging station of Reni,
the level began rising on 10–11 August (Figure 2). The maximum level was reached
on 2 September (413, 431, and 350 cm above gauging station zero, respectively).
The maximum level exceeded the mean level before the release of water from the
reservoir by 320, 270, and 230 cm, respectively, which indicates that the release
wave moving along the Lower Danube was gradually smoothed out. Two release
wave peaks similar to those at Calafat should be noted: at Zimnicea on 25 and 30
August, at Giurgiu on 24 and 30 August, at Oltenita on 25 and 31 August, at Нirsova
on 25 August and 2 September. There was only one peak at Reni.
Therefore, on the Lower Danube, there was no catastrophic flood because of the
regulating capacity of the reservoirs. The maximum levels during the release of water
from the reservoir (at the end of August and early in September) were far below the
historical maximum. As the release wave moved downstream, the difference
between the maximum levels on the Lower Danube and the historical maximum
levels decreased. For example, at the Bulgarian gauging station of Novo Selo it was
387 cm, at the Romanian reach between Calafat and Braila it fell from 386 to 208 cm,
and at the Ukrainian gauging station of Reni it was only 205 cm. The release wave
moved from Calafat to Reni (668 km) in 11 days at the rate of 60.7 km/day, or 0.70
m/s.
On the Ukrainian reach of the Danube, the maximum level of 350 cm above the Reni
gauging station zero on 2 September corresponds to the river water discharge of
8900 m 3 /s. This discharge is far below the Danube mean maximum annual discharge
at the head of the delta (11800 m 3 /s). In the Chilia Branch of the Danube delta, the
maximum level rise in early September of 2002 was even less than that on the neardelta
reach (Reni). This is explained by а significant decrease in the level range
during the movement of the flood and release wave in the delta because of the
stabilizing impact of the sea, where seasonal level changes do not exceed 0.3–0.4 m
(Hydrology…, 2004; Mikhailov et al., 2004).

3 SPRING–SUMMER FLOOD IN MARCH–JUNE 2006
3.1 Synoptic situation preceding the flood
The spring–summer flood period in the Danube River basin (in particular in its middle
and lower parts) is the main and well-defined phase of river water regime. This flood
period is caused by snow melting and rains. Along the Lower Danube, the spring–
summer flood period usually falls on March–July. The <strong>extreme</strong> spring flood in 2006
(by dates and duration) was similar to analogous spring floods in other years, but
was heavier. Spring 2006 in the Danube River basin was moderately warm and
moist. The quantity of precipitation during three spring months has considerably
exceeded monthly norm: in March by 55%, in April by 35%, and in May by 6%.
Monthly average air temperatures were close to normal.
Early in summer, the weather on the upper and middle reaches of the Danube River
was characterized by cyclonic activity with heavy storm rainfall. The monthly sums of
precipitation in June amounted 90% of normal.
Main causes of the <strong>extreme</strong> spring–summer flood in March–June 2006 were, firstly,
great snow supply accumulated by the beginning of March both in mountain areas
and on the plain; secondly, warm weather at the beginning of spring (March–April),
promoted active snow melting; and thirdly, heavy rains in spring months.
3.2 Development and transformation of the Danube spring–summer flood
When analyzing the development and transformation of the spring–summer flood in
March-June 2006, daily water levels from 29 <strong>hydrological</strong> gauging stations along the
Danube River from its upper reach to the sea (Figure 1) were used as the initial
information. The maximum water levels during the spring–summer flood 2006, and
historical maximum levels are resulted in Table 2 (Mikhailov et al., 2008).
In 2006 at some gauging stations of the Middle Danube (Nagymaros, Budapest,
Zemun and Bazias) and at the majority of gauging stations on the Lower Danube
(from Turnu-Severin to Reni a little above the delta head), historical maximum levels
were exceeded in 2006 (Table 2). The greatest excess of <strong>extreme</strong> levels during the
spring–summer flood 2006 above the historical maxima was observed at the gauging
stations on the Romanian and Bulgarian reaches of Danube River and reached 60
cm (Calafat), 51 cm (Lom), 39 cm (Zimnicea), 37 cm (Hirsova), and 60 cm (Braila).
As a result of this complex influence of snow and rain feed, two waves of the spring–
summer floods have been formed (in March–April and at the end of May – the
beginning of June, correspondingly). At the gauging stations on the Upper Danube,
the highest water levels were noted at the end of March – the beginning of April
(Table 2), i.e. during the passage of the first flood wave (the height of the flood wave
has increased from 3–3.5 m (Ingolstadt, Regensburg) to 4.5–5.5 m (Passau,
Kienstock).

Table 2.Maximum spring–summer flood levels, March–June 2006, and historical maximum levels at gauging stations on the Danube
River. Dash means lack of information.
№ Gauging
station
Country
Distance from port of Sulina
(without brackets) and from
the Prorva branch mouth
(in square brackets) (km)
Spring–summer flood in March–June
2006
Maximum level above
gauging station zero
(cm)
Historical maximum (in ice-free period)
Date Period Level
(cm)
1 Ingolstadt Germany 2458 476 11.03 1827–2005 778 18.06.1910
2 Regensburg Germany 2376 523 30.03 1884–2005 666 28.03.1988
3 Passau Germany 2225 863 29.03 1877–2005 1230 10.07.1954
4 Linz Austria 2135 613 29.03 1893–2005 963 11.07.1954
5 Kienstock Austria 2015 789 30.03 1830–2005 1085 14.08.2002
6 Bratislava Slovakia 1869 829 2.04 1823–2005 986 16.08.2002
7 Nagymaros Hungary 1695 713 4.04 1876–2005 707 18.08.2002
8 Budapest Hungary 1647 856 4.04 1876–2005 845 17.06.1965
9 Mohach Hungary 1447 931 8,9.04 1876–2005 984 19.06.1965
10 Bezdan Croatia 1425 734 10.04 1876–2005 776 24.06.1965
11 Bogojevo Croatia 1367 791 10.04 1890–2005 817 15.06.1965
12 Novi Sad Serbia 1255 745 12.04 1888–2005 778 30.06.1965
13 Zemun Serbia 1173 783 17.04 1876–2005 757 26.03.1981
14 Bazias Romania 1072 807 15–17.04 1874–2005 795 06.04.1942
15 Orsova Romania 955 2450 01.06 1971–2005 2568 17.10.1994
16 Turnu-Severin Romania 931 928 27 04 1879–2005 906 28.03.1981
17 Novo Selo Bulgaria 834 922 20 04 1941–2005 900 28.03.1981
18 Calafat Romania 795 861 22,23.04 1879–2005 801 29.03.1981
19 Lom Bulgaria 743 985 23.04 1921–2005 934 29.03.1981
20 Zimnicea Romania 554 839 24.04 1879–2005 800 02.06.1970
21 Giurgiu Romania 493 822 24.04 1879–2005 795 02.06.1970
22 Olenita Romania 430 809 24.04 1879–2005 784 1897
23 Hirsova Romania 253 764 25.04 1898–2005 727 04–06.06.1970
24 Braila Romania 170 699 26.04 1874–2005 639 28.05.1970
25 Reni Ukraine 127 [163] 562 26.04 1921–2005 555 28.05.1970
26 Izmail Ukraine [94] 400 25.04 1921–2005 420 22.05.1970
27 Kiliya Ukraine [47] 249 2.05 1921–2005 282 02.04.1942
28 Vilkovo Ukraine [18] 189 1.05 1921–2005 191 19.02.1979
29 Primorskoye Ukraine 0 538 1.05 1951–2005 599 19.02.1979
Date

At the gauging stations on the Middle Danube (from Bratislava to Bazias), two waves
of the spring flood also became apparent: from the middle of March to the beginning
of May and in the first half of June (Figure 3). Rain floods have gradually merged with
two waves of the spring flood, and by the end of the middle reach, waves were
smoothed out. The <strong>extreme</strong> levels on the Middle Danube were observed later, than
on the Upper Danube – from the beginning to the middle of April, i.e. also during the
first wave of spring flood wave.
900
800
Н, cm
Bratislava
900
800
Н, cm
Novi Sad
700
700
600
600
500
500
400
400
300
300
200
200
100
100
0
0
1.2
15.2
1.3
15.3
29.3
12.4
26.4
10.5
24.5
7.6
21.6
5.7
1.2
15.2
1.3
15.3
29.3
12.4
26.4
10.5
24.5
7.6
21.6
5.7
2600
2500
2400
2300
2200
2100
2000
1900
1800
1.2
15.2
1.3
Н, cm
15.3
29.3
12.4
26.4
10.5
Orsova
24.5
7.6
21.6
5.7
1000
900
800
700
600
500
400
300
200
100
0
1.2
Н, cm
15.2
1.3
15.3
29.3
12.4
26.4
Turnu-Severin
10.5
24.5
7.6
21.6
5.7
1000
900
800
700
600
500
400
300
200
100
0
1.2
900
Н, сm Calafat 800
Н, cm
Reni
15.2
1.3
15.3
29.3
12.4
26.4
10.5
24.5
7.6
21.6
5.7
Figure 3. Level variations at some gauging stations on the Middle and Lower
Danube, March–June 2006
700
600
500
400
300
200
100
0
1.2
15.2
1.3
15.3
29.3
12.4
26.4
10.5
24.5
7.6
21.6
5.7

Significant rise of the water levels exceeding historical maxima was noted at the
upper boundary of the Middle Danube (at Nagymaros and Budapest). Here, the
additional water inflow of a large left tributary of the Morava affected on the levels
rise. Below the confluence of the Danube tributaries – the Sava and the Tisza,
historical maximum levels were exceeded at the gauging stations of Zemun and
Bazias.
Along the Middle Danube, the height of the spring–summer flood quickly increased
from 5.5 m (Bratislava) up to 6.5–7.0 m (Nagymaros, Budapest). At Bazias in a zone
of influence of Iron Gate-I reservoir, the level rise was about 2.5 m.
The spring–summer flood 2006 had the <strong>extreme</strong> character on the Lower Danube
(especially on the reach between Calafat and Braila). The <strong>hydrological</strong> regime of the
Lower Danube is determined by the Iron Gate I reservoir, which is located in a gap
between the Carpathians and the Balkans (943 km from the sea).
In 2006, the water level regime on the Lower Danube was transformed by an artificial
release of water. On a peak of spring–summer flood, water levels in the reservoir
were close to a level of dead storage. During the release of maximal discharges of
the spring–summer flood, its regulating ability has been completely exhausted.
From Turnu-Severin to Reni, <strong>extreme</strong> water levels were observed during the first
flood wave at the end of April. On this reach, the water levels exceeded historical
maxima (Table 2).
On the Ukrainian reach of the Danube River, the greatest levels were observed at the
end of April – the beginning of May and did not exceeded historical maxima. It could
be explained by flood wave “smoothing out” seaward, typical to for all river mouth
reaches, where seasonal level fluctuations are minimal (Mikhailov et al., 2008).
The spring–summer flood on the Lower Danube caused strong flooding. Only in
Romania. nearly 90000 ha of cropland, 1000 km of roads were submerged. About
147 settlements got to disaster area, 227 houses were completely destroyed, 800
houses were damaged, and 12000 people were evacuated.
4 LOW WATER PERIOD (DROUGHT) IN AUGUST–OCTOBER 2003
4.1 Synoptic situation preceding low water period
In the Danube River basin, winter 2002–2003 was cold, and snow supply at the
beginning of March was significant. However, spring 2003 turned out long and cold,
and the most part of melt water sink into the soil, and it was observed a serious
deficiency of precipitation not only on the Lower Danube, but also in the whole river
basin. Therefore, instead of usual water level rising, it was reported gradual falling.
A remarkable deficit in rain and snow was reported by the Danube River basin in
2003. In Germany, a long-term drought between February and September was
caused by the stability of anticyclone weather conditions. Hence the air temperature
and sunshine duration exceeded the annual mean values and altogether ten months
of the year were drier than average.

The total loss of water from plant transpiration and evaporation from the ground was
high in several parts of the Danube River basin and may even be higher than the
amount of snow and rain falling. Many meteorological stations in Germany recorded
the hottest summer ever observed. In the other upstream countries, low precipitation
(rain, snow) and excessive temperatures were reported in 2003 as well. In the lower
part of the Danube River basin the weather was also warmer when compared to the
average climatic pattern.
4.2 Development of the Danube drought
At the end of the summer, the water level fell to the low levels, especially on the
Lower Danube. However, at gauging stations of Orsova, Turnu-Severin, there was no
а pronounced low water period and minimum-recorded values. Some information
about the low water period and historical minimum levels at some gauging stations
on the Lower Danube are presented in Table 3 and Figure 4.
Table 3. Low water period, August–October 2003, and historical minimum levels at
gauging stations on the Lower Danube. Dash means lack of information.
№ Gauging
station
Distance
from port of
Sulina and
from the
Prorva
branch
mouth (in
square
brackets)
(km)
Low water period in Historical minimum (in ice-free period)
August-October 2003
Minimum
level
above
gauging
station
zero
(cm)
Date Period Level
(cm)
Date
17 Novo Selo 834 -37 5.09 1941–2007 –52 22.01.1985
18 Calafat 795 –116 5.09, 3.10 1921–2007 –87 04.01.1954
19 Lom 743 12 5.09 1921-2007 9 23.01.1985
20 Zimnicea 554 –66 7.09 – – –
21 Giurgiu 493 –144 8.09 1921–2007 –126 12.09.1990
22 Olenita 430 –59 8.09 1921–2007 –110 24.10.1947
23 Hirsova 253 –125 6–8.09 1921–2007 –123 10,11.10.1992
24 Braila 170 –1 5,6.09 1921–2007 –61 14.01.1954
25 Reni 127 [163] –13 10.09 1921–2007 –66 28.10.1921
26 Izmail [94] 6 4.09 1921–2007 –30 31.10,1.11.1921
27 Kiliya [47] 5 4.09 1921–2007 –23 31.10.1929
28 Vilkovo [18] 43 1.09 1922–2007 –20 11.03.1929
On the Romanian reach of the Danube, the water level at Calafat and Lom had
reached а minimum-recorded values on 5 September (–116 and 12 cm in relation to
gauging station zero correspondingly). In the period from 1 June to 5 September, the
levels at these gauging stations were lowered by 280 and 297 cm.
At Zimnicea, Giurgiu, Oltenita, and Hirsova, the level changed in а similar way. At
Giurgiu and Hirsova, by 8 September, the level dropped by 315 and 337 cm,
accordingly. In Giurgiu, and Hirsova, the historical minimum levels were recorded on
8 September, (–144 and –125 cm in relation to gauging station zero).

800
H, cm
700
600
Turnu-Severin
500
400
300
200
100
0
1.6
14.6
27.6
10.7
23.7
5.8
18.8
31.8
13.9
26.9
9.10
22.10
250
200
H, cm
Calafat
150
100
50
0
-50
-100
-150
1.6
14.6
27.6
10.7
23.7
5.8
18.8
31.8
13.9
26.9
9.10
22.10
350
300
250
200
150
100
50
0
200
H, cm 150 H, cm
Giurgiu
Lom
100
50
0
1.6
14.6
27.6
10.7
23.7
5.8
18.8
31.8
13.9
26.9
9.10
22.10
-50
-100
-150
-200
1.6
14.6
27.6
10.7
23.7
5.8
18.8
31.8
13.9
26.9
9.10
22.10
250
200
150
100
250
H, cm Hirsova
H, cm
200
Reni
150
50
0
-50
-100
-150
1.6
14.6
27.6
10.7
23.7
5.8
18.8
31.8
13.9
26.9
9.10
22.10
100
50
0
-50
1.6
14.6
27.6
10.7
23.7
5.8
18.8
31.8
13.9
26.9
9.10
22.10
Figure 4. Level variations at some gauging stations on the Lower Danube, August–
October 2003
At the Ukrainian gauging station of Reni, the level changed too. Over the period from
1 June to 4 September, the level dropped by 209 cm. The minimum was reached on
10 September (–13 cm in relation to gauging station zero). This level corresponds to
the river water discharge of 2130 m 3 /s. This discharge is below the Danube mean
minimum annual discharge at the head of the delta (3010 m 3 /s).
In the Chilia Branch of the Danube delta, level drop in August–October of 2003 was
even less than that on the near-delta reach (Reni). This is explained by backwater
effect of the Black Sea level (Hydrology…, 2004).

The rise of water level on 14 September, observed at the gauges stations in the delta
and near-delta reach, was caused by positive storm surge in the Danube River
mouth area.
5 CONCLUSIONS
The formation and transformation of the Danube catastrophic rainfall flood in August
2002 and <strong>extreme</strong> spring–summer flood in March–June 2006, and the preceding
synoptic conditions were considered. In 2002, torrential rains on the Upper and
Middle Danube triggered two <strong>extreme</strong> rainfall flood waves. At some gauging stations
on the Middle and Lower Danube (Bratislava, Budapest, and others), the August
flood levels exceeded historical maxima and caused a catastrophic inundation.
Owing to the timely release of water from the Iron Gate reservoir, the rain flood was
smoothed out and turned into a flat release wave on the Lower Danube. The <strong>extreme</strong>
spring–summer flood in March–June 2006 was resulted from simultaneous melting of
a great snow supply and plentiful rains in the Danube Basin. At a number of gauging
stations on the Lower Danube, water levels also exceeded historical maxima.
A low precipitation (rain, snow), reported by the Danube River basin in 2003, and the
hottest summer led to the formation of the <strong>extreme</strong> low water period in August–
October 2003, when water levels on the Lower Danube fell to the lowest marks.
In the future, global climate warming, intensification of synoptic processes, increment
in the total amount of precipitation and its irregularity can result in an increase in a
frequency of <strong>extreme</strong> <strong>hydrological</strong> <strong>events</strong>. Information about the <strong>extreme</strong> <strong>hydrological</strong>
<strong>events</strong> taking place in the Danube Basin can be of interest of researchers because
many rivers are subject to a strong effect of climatic changes and can have similar
regime features.
Acknowledgments
This work was supported by the Russian Foundation for Basic Research (grant №07-
05-00406).
References
Die Donau und ihr Einzugsgebiet. Eine hydrologische Monographie. 1986: Teil 2. Tabellen. Regionale
Zusammenarbeit der Donauländer.
Hydrology of the Mouth Area of the Danube. 1963: Gidrometeoizdat, Moscow. In Russian.
Hydrology of the Danube Delta. Ed. Mikhailov, V.N. 2004: GEOS, Moscow. In Russian.
Mikhailov, V.N., Mikhailova, M.V., Morozov, V.N., Kornilov, M.V. & Khudoleev, V.N. 2004:
Catastrophic flood on the Danube River in August 2002. Russian Meteorology and Hydrology. 1(53–
58).
Mikhailov, V.N., Morozov, V.N., Cheroy, N.I., Mikhailova, M.V., Zav’yalova, E.F. 2008: Extreme flood
on Danube in 2006. Russian Meteorology and Hydrology. 1(80–89).