chapter - Atmospheric and Oceanic Science

Physiography and Hydrology
In the Brazilian state of São Paulo the area of primary forest has fallen from 58%
to near 8% at the end of the twentieth century. In the state of Paraná, the forest covering
felt from 83% in 1890 to 5% in 1990. In 1945 55% of the East side of the
Paraguay was forest; in 1990 it was only the 15% (Fig. 4.5).
Fig. 4.5. Wooded area in the Eastern Paraguay in hectares.
[Source MAG-GTZ]
In Brazil, in the basin of the Ibicuí River, a tributary of the Uruguay where rice
is produced with irrigation, the conflict is among the rice' farmers and the cities of
the region that need water for the domestic consumption. In Argentina, the cereals
and oleaginous sowed areas increased from 20 to 26 million hectares in the last
decade. The areas of cereal production have increased in order to include the areas
that are marginal to cereals, where the intensive production introduces high risks of
degradation of the soil. This is a matter of concern since the organic content of the
floor has fallen in 50% from its value at the beginning of the twentieth century,
reducing the soil capacity to assimilate water. The introduction of the direct sowing
in the cultivations is growing quickly, driving to certain restoration of the arable
area, and being another factor of change in the hydrological cycle.
The economy of Paraguay which is totally inside the La Plata basin, is highly
dependent on agriculture, 90% of which is cattle production; however its grain
production, at the moment around 10 million tons, is increasing as a result of new
technologies.
Deforestation and deterioration of the ecosystems are critical factors as a consequence
of the expansion of the agriculture in the last decades. It has meant the
disappearance of the forest coverings that were a decisive part of the functioning of
the ecosystems and of the hydrology. One of the acute cases has been the deforesta-
57