Rainfall Variability in Southwestern Colombia: Changes in ENSO-Related Features

The El Nino–Southern Oscillation (ENSO) is the main phenomenon causing interannual rainfall variability in many parts of the globe. Its influence on Southwestern Colombia rainfall was examined using observational and reanalysis data during the 1983–2016 period. In order to focus on the interannual timescale, the data were filtered at the 3–6-year scale. The relations between variables were analyzed with total and partial correlations. The total correlations show consistent relationships between the sea surface temperature (SST) anomalies in the tropical Pacific and the rainfall variations in Colombia such that the rainfall in the Andean Region (AR) relates to the SST anomalies in the central Pacific, and the rainfall in the Pacific Region (PR), or Pacific western plains, relates to the SST anomalies in the eastern Pacific. Partial correlations, excluding the Oceanic Nino Index (ONI) influence, show that AR rainfall is partly modulated by a west–east SST gradient between the eastern tropical Pacific and the tropical North Atlantic (TNA). The partial correlation analyses indicate that the rainfall in the PR is modulated by the SST anomalies in the eastern Pacific; for example, an anomalous SST pattern with simultaneous warming north of 10° S and cooling south of 10° S relates to positive rainfall anomalies in the PR. This SST anomaly dipole in the eastern Pacific is associated with an asymmetric anomalous low-level wind pattern about 5° S, with southeasterlies to the south and southwesterlies to the equator which contribute to increase moisture transport into most of the western plains of Colombia and Ecuador and in part of the western Andes mountain range. Conversely, an opposite-sign SST anomaly pattern in the eastern Pacific and reversed anomaly wind pattern relate to negative rainfall anomalies in the PR. These results establish the foundation for rainfall differential modeling in Southwestern Colombia based on the Pacific SST variations.