chapter - Atmospheric and Oceanic Science

Regional precipitation trends
The precipitation changes have not occurred simultaneously over the entire
region. Positive trends in southern Brazil and northeastern Argentina started sometime
around the middle of the 1970 decade (Fig. 5.3a, b), apparently related to
stronger intensity El Niño (Barros and Doyle 1996; Barros et al. 2000). In the
southern and central portions of subtropical Argentina (Provinces of Buenos Aires,
Cordoba and La Pampa), the strong positive trend started at the end of the 1960s
decade (Fig. 5.3c, d). This occurred simultaneously with the notable warming of the
western hemisphere Antarctic coastland and islands, and probably is related to the
southward displacement of the South Atlantic Anticyclone (Barros and Doyle 1996;
Barros et al. 2000). However, it is also likely that warming of the western South
Atlantic Ocean is also related (Liebmann et al. 2004).
Fig. 5.3. Time series of annual precipitation and their linear trends for: (a)
Córdoba, (b) Buenos Aires, (c) Monte Caseros, and (d) Corrientes.
b. Seasonal trends
We have just discussed the annual precipitation trends. However, the precipitation
increase is not evenly distributed along the year (Castañeda and Barros
2001). According to figure 5.4, the largest positive trends are found during Summer
and Autumn while negative trends of smaller magnitude are found during Spring
over Brazil and during Winter over Uruguay, southern Brazil, and Buenos Aires.
The positive precipitation trend during Autumn affects the Upper Paraná basins
after 1980.
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