Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → Argentine → Interannual variability of rainfall and its relationship with some global circulation indexes for the pampean prairie

Universidad de Buenos Aires (1999)

Interannual variability of rainfall and its relationship with some global circulation indexes for the pampean prairie

Scian, Beatriz Viviana

Titre : Interannual variability of rainfall and its relationship with some global circulation indexes for the pampean prairie

Variabilidad interanual de la precipitación en la Pradera Pampeana y su relación con algunos índices de circulación atmosférica

Auteur : Scian, Beatriz Viviana

Université de soutenance : Universidad de Buenos Aires

Grade : Doctor en Ciencias de la Atmósfera 1999

Résumé
In this study the relationship between anomalies in the pampean prairie precipitation and the anomalous behaviour of the atmospheric circulation, particularly focused on the Southern Oscilation Index (SOI) and the sea surface temperature anomalies in the equatorial Pacific (SST3) is examined. Data consist of secular month precipitation for more than 40 selected stations over the pampean plains. A comparison between different precipitation indexes based on agricultural, climatic and hydrological concepts is performed. In analyzing extreme events, such as drought, the Standarized Precipitation Index (SPI) or IPE in spanish, shows adequacy at a variable time scale. It has shown good properties when monitoring drought or wet episodes in the region, particularly, when classifying extreme conditions. Three coherent subregions in the central pampas of Argentina, Southwest, North and East, respectively were determined by clustering methods. The results indicate that precipitation over the whole region is significantly influenced by the SO phenomenon. A leading SOI correlated with the summer (Nov-Dec-Jan) anomalous rainfall shows significant coefficients, at 5% significance level, from June to August (peak values of -0.56, for August SOI-December IPE). A negative sign implies an anomalous position of the Pacific High that gives rise to negative SOI starting from June onwards, which in turn would produce positive anomalies in November and December precipitation. A positive SOI phase for the same two months, would be related to negative rainfall anomalies. Correlations were performed too, between monthly SPI values and the sea surface temperature of the Equatorial Pacific Niño3, SST3. From the latter, possitive and maximun coefficients result for the East and North regions, with values of 0.58 for each of July SST3 -December IPE and October SST3 November IPE, respectively. The Southwest portion reaches only a coefficient of 0.38 for October SST3 - November IPE, suggesting a Stronger SOI impact on the southwest prairies rainfall compare to that of the SST3. Anomalous precipitation for warm and cold events as defined by Ropelewski and Halpert (1996) have extreme values for spring and early summer. Maximum out of phase values between the two cases is reached in November and December, being the latter the extreme wet. A second and weaker peak occurs 4 to 7 months later. In order to clarify this behaviour SPI anomalies are analized through the SOI five phases established by Stone and Auliciems (1992). Results from the region evidence that : phases 2 and 4 are related to a negative shift in the median precipitation (rainfall deficit), while phases 1 and 3 are associated with a positive shift in median precipitation. Nevertheless, small perturbations during a positive or negative SOI cycle may produce opposite results. A significatively positive shift during March in phase 4 was observed in the period from 1941-1988, when an increase in summer rainfall during phase 1 and phase 3 had been expected as a consecuence of the high positive precipitation trends of the last decades in the region. Significative median rainfall shifts (a=0.05) for November and December are able to be forecasted from SOI conditions starting on July phases. August is the best predictor SOI month for December rainfall anomalies in the Southwest region. It shows four significative phases, 2 and 4 producing negative IPE shifts, and 1 and 3 positive ones.

Mots clés : ANOMALIAS DE PRECIPITACION ; SOI ; SST3 ; INDICE DE PRECIPITACION ESTANDARIZADO ; CLUSTERS ; CORRELACIONES ; EPISODIO CALIDO ; EPISODIO FRIO ; FASES DEL SOI ; PRADERA PAMPEANA ; PRECIPITATION ANOMALIES ; SOI ; SST3 ; STANDARIZED PRECIPITATION INDEX ; CLUSTERS ; CORRELATIONS ; WARM EVENT ; COLD EVENT ; SOI PHASES ; PAMPEAN PRAIRIE

Présentation (Biblioteca Digital)

Version intégrale

Page publiée le 1er octobre 2017, mise à jour le 13 février 2020