ABSTRACT In a tropical montane catchment of the Colombian Andes (Abanico del Quindío), we analysed a 7‐year (2018–2025) monthly record of precipitation isotopes (δ 2 H and deuterium excess) using a novel combination of Seasonal–Trend decomposition (STL) and generalised additive models (GAMs). This approach separates intra‐ and interannual variability and quantifies their climatic drivers. Results reveal a pronounced seasonal δ 2 H cycle (~80‰–100‰ amplitude) driven by a strong amount effect: rainy months yield more negative δ 2 H, whereas drier periods show more positive values. The δ 2 H and deuterium excess values co‐vary seasonally, but their interannual responses diverge under ENSO influences: δ 2 H is more positive during El Niño conditions (positive MEI.v2) and more negative in La Niña, whereas deuterium excess values show the opposite pattern, rising during La Niña (consistent with enhanced continental moisture recycling) and dropping in El Niño. After 2019, coincident with a prolonged ‘triple‐dip’ La Niña, the seasonal δ 2 H peak shifted ~1 month earlier and its amplitude dampened (~20% reduction), reflecting modified rainfall seasonality. GAM results further indicate that precipitation amount and Atlantic SST anomalies (TNA index) significantly predict δ 2 H variability ( p < 0.001), while ENSO (MEI.v2) adds no independent explanatory power after controlling for these factors. For deuterium excess values, the GAM yields significant positive effects of TNA and precipitation and a negative effect of MEI.v2. The best‐fit model explains 86% of δ 2 H variance and 62% of deuterium excess variance, underscoring the strength of this integrated STL–GAM approach for unravelling multi‐scale climate controls on precipitation isotopes in tropical mountains.
Toro-Espitia et al. (Wed,) studied this question.