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

SAURRAL, RAMIRO; CAMILLONI, INÉS; BARROS, VICENTE

INTERNATIONAL JOURNAL OF CLIMATOLOGY

JOHN WILEY & SONS LTD

Lugar: Londres; Año: 2017 vol. 37 p. 1774 - 1793

0899-8418

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 paperuses monthly quality-controlled precipitation data from rainfall stations withcontinuous observations during at least 100 years to quantify long-term trendsas well as interannual-to-centennial variability. Several statistical methodsare applied to the data, primarily to detect jumps and look for changes due torelocation of the gauge stations, as well as to identify significant trends.Most of the regions have registered an increase in annual rainfall, largelyattributable to changes in the warm season. On the other hand, during wintermost stations in Argentina and Brazil do not have significant trends, although eastern Patagonia registered an increase in precipitation and Chile, a marked decreasein rainfall. In order to look into the physical mechanisms behind the observed variability, the changes in mean sea level pressure and precipitable water arequantified for different sub-periods. Also explored is the variability relatedto the Hadley cell width and strength over the region around SSA. Results showthat the Hadley cell has shrunk 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 withan increase of the low-level moisture advection, favoring more rainfall.