Low‐frequency variability and trends in centennial precipitation stations in southern South America

Abstract

Southern South America (SSA), considered as the continental region south of 20°S, has experienced significant precipitation variability and trends in the last decades. This article uses monthly quality‐controlled precipitation data from rainfall stations with continuous observations during at least 100 years to quantify long‐term trends as well as interannual‐to‐centennial variability. Several statistical methods are applied to the data, primarily to detect jumps and look for changes due to relocation of the gauge stations, as well as to identify significant trends. Most of the regions have registered an increase in annual rainfall, largely attributable to changes in the warm season. On the other hand, during winter most stations in Argentina and Brazil do not have significant trends, although eastern Patagonia registered an increase in precipitation and Chile, a marked decrease in rainfall. In order to look into the physical mechanisms behind the observed variability, the changes in mean sea level pressure and precipitable water are quantified for different sub‐periods. Also explored is the variability related to the Hadley cell width and strength over the region around SSA. Results show that the Hadley cell has shrunk and shifted towards the equator in winter over the area, which has caused an enhancement of the sinking motion over much of Argentina, Chile and Brazil, while likely increasing the baroclinicity (and associated precipitation) over Patagonia. In summer, the strength of the subsidence decreased and this was associated with an increase of the low‐level moisture advection, favouring more rainfall. The observational evidence presented here suggests that the zonal asymmetry in the change of the Hadley cell position over SSA could be linked to the presence of the Andes Cordillera.

Influence of Anthropogenically-Forced Global Warming and Natural Climate Variability in the Rainfall Changes Observed Over the South American Altiplano

“…The fact that the positive U200 trends in the Altiplano are significantly related to the South America Hadley cell changes and not with those of the global Hadley cell, might imply that other mechanisms independent of the global tropical expansion are taking place. It is evident that the evolution of the South America Hadley cell exhibits large year-to-year variability (Figure 7A), in agreement with Saurral et al (2017) that analyzed it from NCEP/NCAR reanalyses. It seems then that variability and trends of the Hadley cell over South America could be driven by local sources associated with the South American Monsoon System, as well as remotely by variations associated with the tropical oceans.…”

Statistical downscaling of daily precipitation and temperatures in southern La Plata Basin

“…In the Buenos Aires station, it is possible to observe a progressive growth of summer precipitation mean, with a remarkable increase in the last 5 years, which is in agreement with the findings of Saurral et al . (). Meanwhile, the change to drier conditions in General Pico station is clearly represented by the analogue method and consistent with the results of Maenza et al .…”

“…Several authors have documented the rainfall and temperature trends in southeastern South America, overlapped to a large decadal variability (Penalba and Vargas, ; Rusticucci, ; Maenza et al, ). In the eastern margin of the domain analysed, there is a strong consensus concerning the progressive increase up to the present of annual rainfall mainly due to the increases in rainfall during the summer (de Barros Soares et al, ; Saurral et al, ). Whereas to the southwest, the region underwent a sudden rise in summer precipitation by mid‐1970s owing to the influence of the 1976/1977 climate transition (Agosta and Compagnucci, ), which caused the shift towards the west of the agricultural barrier of the humid Pampas (border between the humid and semi‐arid regions).…”

Hydrological impacts in La Plata basin under 1.5, 2 and 3 °C global warming above the pre‐industrial level

“…In fact, different modes of climate variability such as El Niño‐Southern Oscillation (ENSO) (Camilloni and Barros, ; ; Grimm et al, ; Grimm and Tedeschi, ), the southern annular mode (SAM) (Silvestri and Vera, ) or even anomalies in sea ice extent around Antarctica (Saurral et al, ) lead to distinct patterns of rainfall across the basin, affecting the availability of water over the region. During the last decades, the southern part of LPB has experienced a substantial increase in precipitation (Barros et al, ; Barros et al, ; Barros Soares et al, ; Saurral et al, ) which contributed to expand the extent of the agricultural areas, although at the same time the accompanying increase in extreme precipitation (Penalba and Robledo, ; Doyle et al, ) led to frequent flooding events (Camilloni and Barros, ; Barros et al, ; Camilloni, ).…”