chapter - Atmospheric and Oceanic Science

The positive trends of the mean temperature in Asunción, Paraguay and Santa
Fe, Argentina, are of the same order of magnitude, 0.01ºC/year. Positive trends are
also observed in the RET and the precipitation of both localities The RET trend in
Asunción has a magnitude of 2.6 mm/year, while in Santa Fe is 2.1 mm/year. The
precipitation trends for both localities also have a higher magnitude, between 4 and
5 mm/year. These trends can be visualized in more detail in figure 7.5.
The Argentina locality of Junín shows a mean temperature trend of the order
of 0.01ºC, while the RET trend is only 0.8 mm/year, being one of the lower positive
trend among the analyzed localities. Precipitation, though, presents a 3.9
mm/year positive trend, comparable to Santa Fe.
In the north of the central fringe of the basin, namely in Puerto Casado and
Concepción, though precipitation is more abundant than in the western region, temperature
is very high because of the low latitude. Consequently, the RET is quite
close to precipitation. Therefore, as in the western region, trends in precipitation are
similar to those of the RET. This situation changes towards the South, where as the
temperature decreases, the RET is a considerable lower fraction of the rainfall, and
precipitation trends only reflects partially in the RET trends, thus giving rise to
greater excesses and eventually larger runoffs.
7.4.3. East of Paraguay
Real evaporation trends
The cities of Encarnación and Ciudad del Este, Paraguay, are located in the
basin of the Paraná River, where important precipitation positive trends have been
found (Liebmann et al. 2004) that were also verified with the trends of the Paraná
River and of its tributaries streamflows (Berbery and Barros 2002). Temperature,
RET and precipitation trends are positive in both localities. However, the magnitude
of the temperature trend in Encarnación is very low, of the order of
0.005ºC/year, while in Ciudad del Este is 0.04ºC/year.
Regarding the ETR the difference in the magnitude of the trends is of the
order of 100%. Thus, while in Encarnación the ETR has a trend of 2.5 mm/year, in
Ciudad del Este is of 4.3 mm/year. The precipitation trend shows very different values.
In Encarnación it is of 4.9 mm/year, when in Ciudad del Este reaches 12.2
mm/year.
The hydrological conditions in this region are such that there is a considerable
excess of precipitation over evaporation, which implies that trends in the first one,
considerable exceeds those of the second, since evaporation is in general not
restricted by the lack of water in the soil. Thus, the positive trends in the precipitation
are converted in larger runoffs and streamflows, as it was observed.
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