chapter - Atmospheric and Oceanic Science

From 1956 to 1991, in most of the Argentine territory North of 40 ° S, the
annual precipitation increase was larger than 10%, and even in some regions larger
than 40% (Castañeda and Barros 1994). Largest increases have occurred in western
Buenos Aires Province, East of La Pampa and East of Corrientes. In both, precipitation
increased by more than 200 mm between 1960 and 2000 . The increase
of almost 35% in the West of Buenos Aires case explains the more frequent floods,
and even lands that have become almost permanent lagoons. In Corrientes the
marshes and lakes of the Iberá System have expanded notably their surfaces, except
for a recent drought period when values went back to those of the 1960s.
In subtropical Argentina, the mean precipitation diminishes from West to East
and therefore the isohyets run approximately in a North-South direction. Thus, the
changes in precipitation have resulted in a westward shift of the isohyets. The 600
mm isohyet, which is the approximate western boundary of the agriculture in the
South of the Humid Pampa, shifted more than 200 km toward the West of the
region, while the 800 mm isohyet that is the agriculture boundary in the North shifted
more than 100 km over the Chaco region (Fig. 5.2). For this reason, the land with
aptitude for crop cultivation increased in 100000 km 2 , which together with new
technologies favoured the expansion of the crop farming (Barros et al. 2000b). On
the other hand, the undesired result of the increased precipitation is that some areas
of Buenos Aires, Santa Fe and Corrientes Provinces have seen an increase in floods
and consequently a diminished value of their agricultural activities.
Fig. 5.2.
(a) Mean annual precipitation in the wet Pampa.
[adapted from Barros et al 2000a]
Regional precipitation trends
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600
600
600
800
800
600
800
1000
1000
800
(b) Changes in isohyets since
1950/1969 (black contour)
up to 1980/1999.