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Climate and Geomorphologic-related Disasters in Latin America 17
in tropical regions, together with the human occupation of dangerous and vulnerable
floodplain environments, flood damage can be considerable in urban areas.
Of the large South American fluvial basins, the most dramatic floods take place
in the Parana River Basin. The floods affect a large portion of the population in
Brazil and Argentina, and produce significant economic losses and damage to
infrastructure (Fig. 1.8). With a huge drainage area of 2,605,000 km 2 and a mean
annual water discharge in the middle reach of˜18,860 m 3 /s in Corrientes, this giant
river—one of the ten largest in the world in terms of water discharge—drains a
variety of landscapes and climatic regions in Brazil, Bolivia, Paraguay, and Argentina.
Almost all of the water discharged originates from two subbasins: the Upper
Parana River Basin and the Paraguay River Basin (Table 1.2). With a drainage area
of 1,150,000 km 2 , lying mainly in Brazilian territory, and an absolute maximum
rainfall of more than 2250 mm (in the middle Iguac˛u River tributary basin), the
Upper Paraná River Basin contributes 70% of the water discharged, largely due to
the rainfall produced in southwestern Brazil. The Paraguay River, with a drainage
area of 1,095,000 km 2 , contributes 22.4% of the water discharged, mainly originating
from the Upper Paraguay River Basin, where the Pantanal of Mato Grosso is
located.
The Upper Parana River Basin encompasses the most populated states in Brazil,
including the industrial and agricultural cores of the country. With 24 million
inhabitants, the Metropolitan Region of São Paulo (MRSP), located in the Tiete
River Basin, a tributary of the Parana River, is one of the largest urban agglomerates
in the world and the most important industrial center in South America.
Strong episodic rainfalls on small catchment areas flowing from the Serra do Mar
and Cantareira Mountain Ranges to the Tietê River and its tributary, the Tamanduatei
River, can produce dramatic floods in the São Paulo area. The problems of
inundation on the Tiete River and its tributary began at the end of nineteenth
century, when their floodplains started to be urbanized, especially owing to the
construction of railroads and factories. The main problem was the human modifications
to the original fluvial system. The Tiete was formerly characterized by a
meandering pattern flowing over a broad natural floodplain. However, this channel
has been totally modified by canalization, with large tracts having been cemented,
accelerating the response of the systems to floods but eliminating the floodplain’s
capacity of absorption. The Upper Tietê River Basin in the MRSP has an area of
5985 km 2 and has a mean discharge of 104 m 3 /s, with 30 m 3 /s 1 of this being
effluent. In some months, river discharge is only one-sixth of effluent discharge (see
Chapter 13, for further details). The urban area of the Upper Tiete Basin increased
from 190 km 2 in 1930 to 1900 km 2 in 2001—that is, a tenfold increase in 70 years.
The most intensive and lasting floods occurred in 1924, 1983, 1991, and 2005.
Floods in the Parana River can produce remarkable disasters in Argentina as
well. Along its middle reach, the Parana River flows on a wide and complex
floodplain, 13 to 40 km in width, that is completely inundated during extraordinary
floods. Fluvial stages and discharges have been recorded on the Parana River since
the nineteenth century (1891 to present). In 116 years, the river has reached the
critical stage, necessitating the evacuation of endangered populations 22 times. Very
large floods are considered ‘‘exceptional’’ because of their magnitude. Nevertheless,