Floods in Eastern Subtropical Argentina …
45
being the second largest in South America. The Paraná crosses ESA from north
to south and is a component of the La Plata basin. Its 4,800-km length encompasses a wide basin of roughly 2,600,000 km
2 shared by Brazil, Bolivia, Paraguay,
and Argentina. Precipitation over the upper basin (northern ESA, and Paraguayan
and Brazilian territories) contributes most to mean annual discharges of the Paraná
(Robertson and Mechoso 1998).
Extreme rises of the Parana level are related to the occurrence of El Nino years
(positive phase of the El Niño–Southern Oscillation phenomenon), which exert a
strong influence on the Parana’s inter-annual streamflow variability (Antico et al.
2016). The mean annual streamflow at Corrientes (S) has picked in hydrological
year 1982/83 (S=37,819 m
3 s
−1 ), followed by 1997/98 (S=27,267 m
3 s
−1 ) and
2009/10 (S=23,153 m
3 s
−1 ). The last El Nino phenomenon, 2015/16, has contributed
with an annual streamflow peak of 27,763 m
3 s
−1 , all of them further exceeding
percentile 95th of the historical distribution (S 95p =22,976 m
3 s
−1 in the period
1904/05–2014/15), which shows a historical mean streamflow of 17,225 m
3 s
−1 .
The 1983 flooding was the greatest ever recorded in the past century. Antico et al.
(2016) suggested that the 1983 flooding was consequence of the concurrent effect
of diverse climate quasiperiodic forcing, such as El Niño and the Pacific Decadal
Oscillation, together with the long-term trend related to anthropogenic influence.
The year-to-year variations of precipitation over the middle-upper basin of the
Paraná explain about 40–45% of streamflow variations at the Corrientes gauge
station. Precipitation variations in the middle-lower basin explain about 30–35%
of the inter-annual variation. The latter means that direct precipitation is a weakto-moderate factor influencing the river streamflow variability at inter-annual scale.
Another relevant factor to consider is associated with evapotranspiration, related
to groundwater storage. Some experts from the National Agricultural Technology
Institute point to limited water storage due to changes in the land cover by agricultural purposes as one of the main factors influencing flooding, as in Bertram and
Chiacchiera (2013).
The inter-annual Paraná streamflow variation is highly associated with the terrestrial water storage anomalies (TWSA) from NASA’s GRACE mission (Landerer and
Swenson 2012) within the wide river basin (Fig. 7). It is quite apparent that the interannual Paraná streamflow variation is highly associated with that of the TWSA within
the wide river basin (Fig. 7, panel a). Over 80% of the variance of streamflow can be
explained by the year-to-year TWSA variability in localities over the upper basin of
the Parana. Figure 7, panel b, further shows that there is a positive trend in TWSA
over the upper basin of the Parana along the period in which GRACE data are available. Importantly, previous studies have noted the existence of a capacity limitation
on terrestrial water storage that is associated with regional flooding (Crowley et al.
2006; Reager et al. 2009). The result points to the high potential risk of Paraná’s
flooding due to limited water storage capacity in the basin. Furthermore, there is
an apparent positive trend in TWSA over the upper basin of the Parana along the
period in which GRACE data are available. The latter certainly depends on the rate
of deforestation and land changes over the river basin, besides precipitation.
45
being the second largest in South America. The Paraná crosses ESA from north
to south and is a component of the La Plata basin. Its 4,800-km length encompasses a wide basin of roughly 2,600,000 km
2 shared by Brazil, Bolivia, Paraguay,
and Argentina. Precipitation over the upper basin (northern ESA, and Paraguayan
and Brazilian territories) contributes most to mean annual discharges of the Paraná
(Robertson and Mechoso 1998).
Extreme rises of the Parana level are related to the occurrence of El Nino years
(positive phase of the El Niño–Southern Oscillation phenomenon), which exert a
strong influence on the Parana’s inter-annual streamflow variability (Antico et al.
2016). The mean annual streamflow at Corrientes (S) has picked in hydrological
year 1982/83 (S=37,819 m
3 s
−1 ), followed by 1997/98 (S=27,267 m
3 s
−1 ) and
2009/10 (S=23,153 m
3 s
−1 ). The last El Nino phenomenon, 2015/16, has contributed
with an annual streamflow peak of 27,763 m
3 s
−1 , all of them further exceeding
percentile 95th of the historical distribution (S 95p =22,976 m
3 s
−1 in the period
1904/05–2014/15), which shows a historical mean streamflow of 17,225 m
3 s
−1 .
The 1983 flooding was the greatest ever recorded in the past century. Antico et al.
(2016) suggested that the 1983 flooding was consequence of the concurrent effect
of diverse climate quasiperiodic forcing, such as El Niño and the Pacific Decadal
Oscillation, together with the long-term trend related to anthropogenic influence.
The year-to-year variations of precipitation over the middle-upper basin of the
Paraná explain about 40–45% of streamflow variations at the Corrientes gauge
station. Precipitation variations in the middle-lower basin explain about 30–35%
of the inter-annual variation. The latter means that direct precipitation is a weakto-moderate factor influencing the river streamflow variability at inter-annual scale.
Another relevant factor to consider is associated with evapotranspiration, related
to groundwater storage. Some experts from the National Agricultural Technology
Institute point to limited water storage due to changes in the land cover by agricultural purposes as one of the main factors influencing flooding, as in Bertram and
Chiacchiera (2013).
The inter-annual Paraná streamflow variation is highly associated with the terrestrial water storage anomalies (TWSA) from NASA’s GRACE mission (Landerer and
Swenson 2012) within the wide river basin (Fig. 7). It is quite apparent that the interannual Paraná streamflow variation is highly associated with that of the TWSA within
the wide river basin (Fig. 7, panel a). Over 80% of the variance of streamflow can be
explained by the year-to-year TWSA variability in localities over the upper basin of
the Parana. Figure 7, panel b, further shows that there is a positive trend in TWSA
over the upper basin of the Parana along the period in which GRACE data are available. Importantly, previous studies have noted the existence of a capacity limitation
on terrestrial water storage that is associated with regional flooding (Crowley et al.
2006; Reager et al. 2009). The result points to the high potential risk of Paraná’s
flooding due to limited water storage capacity in the basin. Furthermore, there is
an apparent positive trend in TWSA over the upper basin of the Parana along the
period in which GRACE data are available. The latter certainly depends on the rate
of deforestation and land changes over the river basin, besides precipitation.