Multiscale ENSO–Drought Dynamics and Climatic Memory Across Diverse Köppen–Geiger Climate Zones in Ecuador

Drought is a major global hazard, yet critical knowledge gaps persist regarding how the El Niño–Southern Oscillation (ENSO) modulates it in topographically complex equatorial regions. This study characterizes ENSO’s spatiotemporal influence on drought across Ecuador’s four principal Köppen–Geiger climate zones: Amazon, Andean highlands, temperate, and arid coastal. Using meteorological data (1985–2015), we computed the Standardized Precipitation Evapotranspiration Index (SPEI) across multiple timescales. Ten ENSO indices were evaluated using Wavelet Coherence analysis to identify non-stationary, scale-dependent correlations and phase dynamics. Results show that tropical, temperate, and Andean (polar tundra) climates exhibit prolonged climatic memory, with significant ENSO correlations across 1- to 24-month SPEI scales. Conversely, arid regions display shorter memory, with correlations dissipating at longer timescales due to limited moisture storage. Phase analysis reveals two high-coherence intervals (1995–2000 and 2007–2013) at the 3-year return period, in which ENSO indices led drought by 9–18 months, underscoring their predictive potential. At 6- and 11-year periods, ENSO signals generally lag SPEI, indicating prolonged drought retention. The Trans-Niño Index and Southern Oscillation Index proved particularly sensitive for the Amazon–Andes transition. These findings establish a robust framework for improving drought monitoring and climate adaptation in vulnerable equatorial regions.