Variações multidecenais da precipitação na Colômbia e na Bacia do Prata e suas relações com os jatos de baixos níveis

Abstract

The hypothesis investigated in this Thesis is that low frequency natural variations associated with the Atlantic Multidecadal Oscillation (AMO) can have a strong influence on the average behavior of precipitation and streamflow rates over the Colombian Biogeographic Choco (CBC) basins, and in extreme precipitation events over the La Plata Basin (LPB) driven by changes in low-level jets (LLJ) of South America. For this, spatial interpolations and cross-validation, trend and homogeneity tests, principal component analysis (PCA), extreme precipitation indices, and composite analysis were used. The main contributions of this research were: i) the interpolations allowed to examine the data and characteristics of annual and seasonal mean precipitation for the two study areas; through the cross-validation of multivariate geostatistical methods and deterministic methods, Cokriging was identified with the spherical (Gaussian) model as the best precipitation interpolator in the CBC region (in the LPB), using elevation as a secondary variable; ii) regarding the influence of the Atlantic Multidecadal Oscillation (AMO) on the variability of the Chocó Jet (CJ) and the Caribbean Low-Level Jet (CLLJ), there is an increase in the zonal wind in the center of the CJ during September-November (SON), reinforced after 1997, associated with negative sea surface temperature (SST) anomalies in the tropical Pacific Ocean and positive ones in the Caribbean Sea and Tropical North Atlantic (TNA), strengthen the CJ and weaken the CLLJ, enhanced the moisture transport to central and western Colombia, increasing the rainfall there. The results indicate that the combination of the cold phase of the PDO (CPDO) and the warm phase of the AMO (WAMO) defines a low-frequency medium state, which affects the interannual climate variability and can affect the CJ variability and the precipitation In Colombia; iii) the variations in the streamflow of the Atrato River Basin (ARB) during the 1965-2015 period, considering the cold (1965-1994) and warm (1995-2015) phases of the AMO, showed an increase after 1994. The warm tropical Atlantic during WAMO intensified the Walker circulation, causing an upward movement in the north and northwestern South America, which contributed to the positive rainfall anomalies and increased streamflow in the ARB; iv) the seasonal validation of the CHIRPS (Climate Hazards Group Infrared Precipitation with Stations) precipitation dataset for the LPB, through the PCA, indicated that the CHIRPS v.2 dataset captures the spatial patterns and variability at different time scales in the LPB; v) an increase in total wet-day precipitation (PRCPTOT) and number of heavy precipitation days (R10mm) in the southern LPB (S-LPB) during SON, and an increase in the consecutive dry days (CDD) in northern LPB (N-LPB) during June-August (JJA) were observed. An upward change in R10mm after 1999 is identified during SON in S-LPB, associated with: teleconnections with the positive Indian Ocean Dipole (IOD), drives an extratropical southern Rossby wave disturbance extending towards southeastern South America and configures a barotropic cyclone over the south of the continent, and favor the moisture transport from the northwestern and central Amazon to southern and western LPB; and increased moisture flow to LPB due to warming in the southwestern Atlantic. An important aspect discussed here is that the low-frequency background conditions are modulated by the Atlantic Multidecadal Oscillation (AMO). The results, as well as the proposed methods, are of interest for low-frequency climate monitoring and forecasting, for water resources management and hydrometeorological risk in two regions of particular environmental and economic importance in South America.