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L. Zaharia et al.
in summer, autumn and winter (statistically significant only in autumn, for α = 0.01),
while in spring the trend is negative but non-significant. Annually, an increasing trend
in average discharges was detected, but non-significant statistically.
In this chapter, we focused the investigation on the changes observed during
1961–2012, in high flows (floods) and the low flows of the Valea Cerbului River.
10.5.2.1 Changes in the Magnitude and Frequency of Floods
The annual flood peaks of the Valea Cerbului River recorded at Bus , teni g.s. during
the period 1961–2012 occurred most frequently during the summer months, each
with more than 20% of the cases, while the lowest frequencies were recorded during
winter, with no annual floods in January (Table 10.1).
The magnitude of the annual floods (the largest peak flood of each year) has
a statistically significant upward trend (with a level of significance α = 0.1). The
seasonal trends (analyzed based on the maximum monthly discharges averaged for
each season) is consistent with the seasonal trends identified using mean daily and
monthly discharges: significant positive trends in autumn and winter (for α = 0.1)
and non-significant in summer; negative trend in spring, non-significant (Table 10.2).
In order to analyze the temporal variability and frequency of floods (during
1961–2012), we established a threshold discharge, namely three times the mean
multiannual discharge [142, 184]. Any mean daily discharge exceeding the threshold was considered a flood, except consecutive days with such values, which were
counted as single events. This approach allows to include in the analysis of both
exceptional and ordinary floods, for more accurate identification of their temporal
frequency. The interannual variability of the number of floods shows a slight upward
trend, statistically non-significant. The maximum frequency of floods is identified in
1966, 1998, 2005 and 2010, but there are years without floods (defined as mentioned
above): 1976, 1986, 1993, 2002 and 2011 (Fig. 10.10a).
At monthly level, the highest frequency of floods in the analyzed period is met in
June (over 20% of the total number of floods), followed by July (approx. 16%) and
April (almost 12%), when snowmelt is mixed with spring rainfall. The months with
the lowest frequency of floods occurrence are January and February, with less than
2% (Fig. 10.10b).
The decadal analysis of the frequency of floods (as defined above) highlights some
changes during the period 1961–2010. The total number of floods was smaller in the
second and third decades of the analyzed period (1971–1980 and 1981–1990), namely
34 and 31 floods. The maximum number of floods were recorded between 2001 and
2010. The absolute monthly frequency of floods shows a great decadal variability in
March, April and August. The maximum frequency of floods is identified in June
for all decades (Fig. 10.11a).
Except for the first decade considered in the study, the floods were recorded most
often during summer in each decade. In autumn, the frequency of floods for the
L. Zaharia et al.
in summer, autumn and winter (statistically significant only in autumn, for α = 0.01),
while in spring the trend is negative but non-significant. Annually, an increasing trend
in average discharges was detected, but non-significant statistically.
In this chapter, we focused the investigation on the changes observed during
1961–2012, in high flows (floods) and the low flows of the Valea Cerbului River.
10.5.2.1 Changes in the Magnitude and Frequency of Floods
The annual flood peaks of the Valea Cerbului River recorded at Bus , teni g.s. during
the period 1961–2012 occurred most frequently during the summer months, each
with more than 20% of the cases, while the lowest frequencies were recorded during
winter, with no annual floods in January (Table 10.1).
The magnitude of the annual floods (the largest peak flood of each year) has
a statistically significant upward trend (with a level of significance α = 0.1). The
seasonal trends (analyzed based on the maximum monthly discharges averaged for
each season) is consistent with the seasonal trends identified using mean daily and
monthly discharges: significant positive trends in autumn and winter (for α = 0.1)
and non-significant in summer; negative trend in spring, non-significant (Table 10.2).
In order to analyze the temporal variability and frequency of floods (during
1961–2012), we established a threshold discharge, namely three times the mean
multiannual discharge [142, 184]. Any mean daily discharge exceeding the threshold was considered a flood, except consecutive days with such values, which were
counted as single events. This approach allows to include in the analysis of both
exceptional and ordinary floods, for more accurate identification of their temporal
frequency. The interannual variability of the number of floods shows a slight upward
trend, statistically non-significant. The maximum frequency of floods is identified in
1966, 1998, 2005 and 2010, but there are years without floods (defined as mentioned
above): 1976, 1986, 1993, 2002 and 2011 (Fig. 10.10a).
At monthly level, the highest frequency of floods in the analyzed period is met in
June (over 20% of the total number of floods), followed by July (approx. 16%) and
April (almost 12%), when snowmelt is mixed with spring rainfall. The months with
the lowest frequency of floods occurrence are January and February, with less than
2% (Fig. 10.10b).
The decadal analysis of the frequency of floods (as defined above) highlights some
changes during the period 1961–2010. The total number of floods was smaller in the
second and third decades of the analyzed period (1971–1980 and 1981–1990), namely
34 and 31 floods. The maximum number of floods were recorded between 2001 and
2010. The absolute monthly frequency of floods shows a great decadal variability in
March, April and August. The maximum frequency of floods is identified in June
for all decades (Fig. 10.11a).
Except for the first decade considered in the study, the floods were recorded most
often during summer in each decade. In autumn, the frequency of floods for the