chapter - Atmospheric and Oceanic Science

Regional precipitation trends
5.3.2. Frequency of extreme precipitation
Frequency of heavy precipitations in Argentina has increased notably since
the late 1970s (Fig. 5.6). Since that time, the number of recorded cases with precipitations
over 100 mm in less than 48 hours has been three folded in the Centre and
East of Argentina and the same happens with the thresholds of 50 and 1590 mm
(Barros 2004).
Fig. 5.6. Number of cases with precipitation larger than 100 mm.
It should be noted that cases as those documented in figure 5.6 are the ones
that lead to floods, particularly if the terrain favours surface runoff that concentrates
the water in certain areas
Increased frequency of extreme rainfalls has been observed also in southern
Brazil (Xavier et al. 1992 y 1994), especially in summertime. This seems part of a
global trend, which on the other hand should be expected because of the increased
concentration of the greenhouse gasses. This increment would lead to the warming
of the low level troposphere favouring larger water vapour content and a vertical
gradient more unstable as a consequence of the stratospheric cooling. Both
changes, more vertical instability and greater water vapour content favours the
development of the intense rainfall processes
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