Ecuador's Astroclimate, 2010–2025

Country-scale astro-climatology and site-screening for Ecuador, integrating reanalysis, satellite, and geospatial layers into operational products for observatories. From ERA5 (2010–2025) we derive three night-time metrics—photometric clear-sky fraction (CSNF), precipitable water vapour (PWV), and 200-hPa wind speed (V200)—and combine them into an Observing Quality Index (OQI). Independent cloud validation against ISCCP-H (1983–2017 subset) confirms physical credibility (bias = −0.217, RMSE = 0.23, r = 0.76; N ≈ 3.8k grid-months). ENSO composites show coherent, opposing responses: in the Sierra, El Niño raises OQI by +0.022 (95% CI: +0.007 to +0.038) with drier air (PWV +0.65 kg m⁻² anomaly) and weaker upper-level winds (V200 −0.91 m s⁻¹), while La Niña lowers OQI by −0.022 (−0.036 to −0.008) with wetter/stronger-wind conditions. Trends (2010–2025) indicate modest but spatially robust improvements in OQI across many provinces. A calibrated binomial GLM and Monte-Carlo cross-validation provide monthly probabilities of achieving ≥K usable nights (K = 3–15) under Neutral/El Niño/La Niña scenarios for 2026–2028; skill is adequate for planning, and seasonality dominates ENSO at UTN/Ibarra, highlighting operational windows in January, July–September, and October/December.