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\subsubsection{ENSO Indices}  A common ENSO metric is the Southern Oscillation Index (SOI). The SOI represents the difference in normalized surface pressure between Taihiti and Darwin, Australia. Further details regarding its We adopted the  calculation are explained at \cite{NOAA}The method definition proposed by the National Oceanic and Atmospheric Administration \cite{NOAA}. The  index reflects the changes in air-mass fluxes in the tropical Pacific Ocean. This fluxes, are a manifestation of changes in sea surface temperature (SST). The SOI has an open ended scale with positive and negative values. A negative SOI value represents above-average warm SST conditions the eastern tropical Pacific Ocean. This represents an 'El Niño' phase of the phenomenon. El Niño brings wet conditions to the coasts of Southern Ecuador and Northen Peru. The opposite pattern occurs with a positive SOI value, representing a 'La Niña' phase. This index does not establish thresholds to classify the intensity of ENSO events. Another ENSO index is the Oceanic Niño Index (ONI). The ONI measures monthly SST values in the tropical Pacific Ocean. The measurements take place in the region from 5 oN to 5 oS latitude and 120 oW to 170 oW longitude. This is the 'Niño 3.4' region. The index requires the calculation of 3-month running means and its climatology. The ONI is the difference between these two values. An 'El Niño' condition exits if there is at least an anomaly of +0.5 oC in this computation. An anomaly of -0.5 oC indicates a 'La Niña' phase.