chapter - Atmospheric and Oceanic Science

In the case of the Paraná River the relative increase of mean minimum and
maximum flows is similar to that of the mean flow, indicating an increase in the
amplitude (that is, greater variability), while for the Uruguay River such amplitude
has remained practically invariable (Jaime and Menéndez 2002).
Figure 6.4 shows the evolution of the monthly mean flows of the three main
rivers of the basin, including the mean flow of the La Plata River, for most of twentieth
century. From dimple observation, the interannual and interdecadal variability
of the streamflow is inferred. In particular, the increase observed in the second
half of the century.
YEAR
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
(a) La Plata
Cl 5x10 3 m 3 6 –1
(b) Paraná
Cl 3x10 3 m 3 6 –1
Fig. 6.4. Evolution of the mean monthly flows.
Hydrological trends
2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 2 4 6 8 10 12 MONTH
Figures 6.5 and 6.6 show the power spectra of the series of monthly mean
flows of the Paraná and Uruguay rivers, respectively, obtained by means of the
wavelet technique (Jaime and Menéndez 2002). The years of the period of analysis
are shown in abscissas, and in the ordinate axes, the periods of the spectral components.
The level curves represent a measure of the energy (amplitude) of those components.
It is observed that in the Paraná river, the components of around 8-year
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(c) Paraguay
Cl 1x10 3 m 3 6 –1
(d) Uruguay
Cl 3x10 3 m 3 6 –1