chapter - Atmospheric and Oceanic Science

Hydrological trends
In table 6.1 it is presented a list of the 10 largest discharges and ebbs of the
Paraná River of the period 1902-2004, in function of their daily peak flow. It is
observed that 80% of the maximums occur from 1966 on, while all the minimums
were previous to 1950. In the Paraguay River, two thirds of the 16 largest discharge
of the twenty century in Asunción took place during the last fourth of the century.
This deviation toward the occurrence in the last fourth of the century is more evident
the larger the considered discharges were, since out of the more intense 5, 4
were after 1975 (Barros et al. 2004). In the Uruguay River, out of the 16 larger daily
peaks from 1950, none took place before 1970 and only 2 before 1975 (Camilloni
and Caffera 2003). All this illustrates the noticeable impact that the regional climatic
change has caused in the intensity and frequency of the floods in the flood valleys
of the main rivers of the La Plata basin.
Rivers and plain lagoons with relatively small or narrow basins respond
quickly to large precipitations concentrated on one or few days. In the case of the
Salado del Norte River (Argentina), during April 2003 several days with intense
precipitations occurred; in particular, in the days 23 and 24 at least two Mesoscale
Convective Systems (MCS) produced more than 300 mm in less than two days in
towns as distant as the north of Santa Fe and the east of Entre Ríos. This provoked
the catastrophic flood of the city of Santa Fe. The MCS events have given place to
frequent floods in the last two decades in the west, northwest and centre of the
Province of Buenos Aires (Argentina), starting with that of 1982 and culminating
with the October 2001 case. In the south of the Province of Santa Fe similar situations
are seen, even with water transfers between basins, like it is the case of the
significant flood of the Picasa lagoon. In Corrientes the system of lagoons and wetlands
of Iberá grew notably in surface from the 1960 decade, causing big losses to
the owners of the flooded fields. Recently, after a year of drought, the lagoons
retreated considerably.
Table 6.1 Ranking of annual extreme discharges and ebbs of the Paraná River
based on its daily peak flow.
Major discharges Ebbs
Year Flow (m 3 /s) Year Flow (m 3 /s)
1905 56025 1944 7703
1992 54925 1916 7756
1983 53992 1925 7765
1998 52308 1934 7765
1966 48602 1911 7774
1982 48025 1924 7783
1929 41964 1938 7783
1997 41570 1949 7783
1990 41048 1910 7792
1977 40918 1913 7801
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Table 6.1. Ranking of annual
extreme discharges and ebbs of
the Paraná River based on its
daily peak flow.