Typical La Niņa-related impacts in
South America include wetter-than-normal conditions over the Amazon basin and northern
South America, and drier-than-normal conditions over southern Brazil, Uruguay and
northeastern Argentina (Aceituno, 1988; Ropelewski and Halpert, 1989). These average
features display considerable seasonality, with the wetter-than-normal conditions
extending into Northeast Brazil during March–May and being confined to extreme
northern South America during September–December, and the drier-than-normal
conditions farther south being most prominent from September–December.
Many of the precipitation anomalies observed over South America during
1999 (Fig. 55) are consistent with those recorded during past
cold episodes. Above-average precipitation was observed over the Amazon basin during DJF
1998–99 and MAM 1999 (Figs. 55a, b) and over extreme
northern South America throughout the year.
In northern Venezuela the persistent pattern of above-normal rainfall
resulted in saturated soil conditions, and was a contributing factor in producing the
devastating floods and landslides in that country during 14–17 December 1999. High
resolution experimental satellite estimates of precipitation during 15–17 December
indicate that up to 475 mm fell in coastal sections near Caracas (Rod Scofield, NESDIS,
personal communication). Local observations (Luis Hidalgo, personal communication)
indicate that in the vicinity of the coast and along the slopes of the coastal mountains
rainfall totals may have been up to twice as large as the satellite estimates.
Farther south, rainfall deficits accumulated substantially during SON
over southern Brazil, Paraguay, Uruguay (Fig. 57a) and also over
northeastern Argentina (Fig. 57b), consistent with La
Niņa-related conditions. Rainfall deficits for the season exceeded 200 mm in portions of
these regions (Figs. 55d, 57).
In other parts of northern South America, the observed rainfall pattern during 1999
deviated from that expected during cold episodes. For example, coastal Ecuador and
northern Peru experienced above-average rainfall during DJF 1998–99 (Fig. 56a), while portions of northeastern Brazil experienced
rainfall deficits during DJF and MAM (Figs. 56a, b).
