Modulation of Rainfall Variability and Potential Predictability in Ecuador: ENSO’s Evolving Influence (1981-2018)

Abstract

This study examines the modulation of precipitation variability and its implications for potential predictability over mainland Ecuador and its relationship with the El Niño–Southern Oscillation (ENSO) during the period 1981–2018. The analysis integrates homogenized and gap-filled daily precipitation observations with multiple satellite-based datasets (MSWEP, CHIRPS, and IMERG), enabling a comparative assessment of seasonal precipitation characteristics, dry and wet spell indices, and extreme rainfall metrics. Climatic indices derived from sea surface temperature (SST) anomalies in the Niño 1+2, Niño 3, Niño 3.4, and Niño 4 regions are used to evaluate ENSO-related influences.

To assess multidecadal changes, two sub-periods (1981–1999 and 2000–2018) are contrasted. Empirical Orthogonal Function (EOF) analysis and correlation techniques reveal significant shifts in the dominant modes of precipitation variability and in their associations with ENSO indices. Results indicate a reorganization of ENSO-related modulation, with a reduced influence of eastern Pacific SST anomalies and an increased role of central Pacific variability after 2000, particularly affecting dry and wet spell persistence and extreme precipitation indices. These findings highlight a non-stationary ENSO–precipitation relationship in Ecuador, with implications for seasonal predictability, climate risk assessment, hydrology, hydropower and agriculture management and planning in a region characterized by strong topographic and climatic heterogeneity.