Changes in Average Annual Precipitation in Argentina’s Pampa Region and Their Possible Causes

Abstract

Changes in annual rainfall in five sub-regions of the Argentine Pampa Region (Rolling, Central, Mesopotamian, Flooding and Southern) were examined for the period 1941 to 2010 using data from representative locations in each sub-region. Dubious series were adjusted by means of a homogeneity test and changes in mean value were evaluated using a hydrometeorological time series segmentation method. In addition, an association was sought between shifts in mean annual rainfall and changes in large-scale atmospheric pressure systems, as measured by the Atlantic Multidecadal Oscillation (AMO), the Pacific Decadal Oscillation (PDO) and the Southern Oscillation Index (SOI). The results indicate that the Western Pampas (Central and Southern) are more vulnerable to abrupt changes in average annual rainfall than the Eastern Pampas (Mesopotamian, Rolling and Flooding). Their vulnerability is further increased by their having the lowest average rainfall. The AMO showed significant negative correlations with all sub-regions, while the PDO and SOI showed significant positive and negative correlations respectively with the Central, Flooding and Southern Pampa. The fact that the PDO and AMO are going through the phases of their cycles that tend to reduce rainfall in much of the Pampas helps explain the lower rainfall recorded in the Western Pampas sub-regions in recent years. This has had a significant impact on agriculture and the environment.

Changes in the Intensity and Variability of Precipitation in the Central Region of Argentina between 1960 and 2012

“…Thus, although at LB and VD the increasing long-term trend is still significant, both procedures used to analyze the change in trend establish that AR has already reached its maximum and is now decreasing. On the other hand, a progressive decrease of rainfall at VM during the period seems to have led to a decreasing trend, although with a slightly lower significance (p < [40]. On the other hand, the SOI is an atmospheric index with an annual oscillation period and is therefore associated with high frequency variations in rainfall.…”

“…Although the non-homogeneous character of the DPF time series predominates at the three places, this relatively similar trend change at all of them could be considered as evidence that lack of homogeneity is an expression of natural climate variation rather than of a monitoring problem. [40] also showed the existence of teleconnections between climate fluctuation modes (Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and Southern Oscillation Index (SOI)) and precipitation in the Central, Flooding, and Southern Pampa sub-regions of Argentina. The AMO and PDO are ocean oscillations, with cycles of about 40 to 80 years that can be associated with low frequency changes in rainfall [40].…”

“…[40] also showed the existence of teleconnections between climate fluctuation modes (Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and Southern Oscillation Index (SOI)) and precipitation in the Central, Flooding, and Southern Pampa sub-regions of Argentina. The AMO and PDO are ocean oscillations, with cycles of about 40 to 80 years that can be associated with low frequency changes in rainfall [40]. On the other hand, the SOI is an atmospheric index with an annual oscillation period and is therefore associated with high frequency variations in rainfall.…”

“…Using the Hubert's method of segmentation of hydrometeorological time series, [40] show that Argentina's Pampa Region was subject to sudden shifts in average rainfall but, for the Central Pampa sub region of Argentina, annual precipitation augmented in three successive steps, the first from 1941 to 1965, then from 1966 to 1996, and finally, from 1997 to 2002. In the more recent years the rainfall trend returns back to the initial period values.…”

The importance of climate scenarios in setting the productivity indexes in the Pampa Arenosa sub-region of the province of Buenos Aires, Argentina

“…After being drawn across the Brazilian coastline, maritime subtropical air moves southeast, reaching up to 40° latitude in summer and about 30° latitude in winter. In this way, the Pampa Region receives sea winds throughout the year, with a moisture gradient decreasing from east to west (Pérez et al, 2015).…”