Observed and Simulated Summer Rainfall Variability in Southeastern South America

LEANDRO DÍAZ; CAROLINA VERA; RAMIRO SAURRAL

Qingdao

Conferencia; CLIVAR 2016 Open Science Conference; 2016

p { margin-bottom: 0.21cm; direction: ltr; color: rgb(0, 0, 0); }p.western { font-family: "Liberation Serif","Times New Roman",serif; font-size: 12pt; }p.cjk { font-family: "WenQuanYi Zen Hei","MS Mincho"; font-size: 12pt; }p.ctl { font-family: "Lohit Hindi","MS Mincho"; font-size: 12pt; }Theclimate changes observed in the last decades has raised concern amongpolicy and decision makers about the importance of the knowledge andprediction of climate. In particular southeastern South America(SESA) has experimented large positive precipitation trends duringthe 20thcentury that impacted many socio-economic sectors. However, regionalstudies show that decadal variability has a large influence in SESAprecipitation. As a consequence, a deeper knowledge of decadalclimate variability in the region is needed in order to project nearterm future changes with a lower degree of uncertainty. The Fifthphase or the World Climate Research Program-Coupled ModelIntercomparison Project (WCRP/CMIP5) Experiment provides an excellentopportunity to investigate physical processes involved in SESAprecipitation changes and their predictability.Themean precipitation evolution since the last 150 years exhibit in SESAconsiderable multi-decadal variation that have been identified inprevious works as forced by the tropical ocean variability.Therefore, in order to better understand the influence of theobserved large-scale interannual variability of the sea surfacetemperatures on austral summer rainfall in SESA in a global warmingcontext, a singular value decomposition analysis was performed. Thefirst mode shows over the 1902-2010 period, a clear global warmingsignal, mainly related to warming in Pacific and Indian Ocean inassociation with a rainfall increase in SESA. The temporal series ofthe mode exhibits variability going from interannual to interdecadaltrends. Decadal variability is remarkable, with a particular phaseshift at around the middle 1970s. After detrending the series, thefirst mode resembles an El Niño-Southern Oscillation like pattern,which also has a remarkable variability on decadal scales. Moreover,it was found that the relationship between sea surface temperaturevariations, especially in the Tropical Pacific Ocean, and SESAprecipitation is non stationary, exhibiting decadal variations,related with changes in the teleconnections between both regions. Historicaland Decadal simulations of WCRP/CMIP5 coupled general circulationmodels (CGCM) areconsidered in order to make a preliminary evaluation of therepresentation of the australsummer rainfall variability and trends in Southeastern South Americaand its connection with ocean variability. Models are able torepresent a significant positive trend over SESA in agreement withobservations, which could be related to frequency changes in therainfall leading pattern. Representation of the main pattern ofclimate variability was assesed. Preliminaryresults using short-term climate predictions show that thesimulations are able to reproduce the leading mode of variability, aswell as the teleconnection pattern linking the tropicalPacific-Indian Ocean sector with southern South America.