When the ITCZ is at its northernmost position (JJA), cold westerlies flow into Ecuador, whereas during austral summer (DJF), moist winds from easterly directions reach the country. In the first case, the ITCZ excursions throughout the year determine the provenance of air masses with different humidity and temperature conditions. Previous research has established that the climate of Ecuador is indeed controlled by the ITCZ seasonal excursions and complex Andean orography. We propose that the amount of rainfall located at the V-Index region is a more robust approach for explaining the δ 2H p and δ 18O p variability rather than the local amount. Precisely, this convergence is stronger at the V-Index region (5° S–5° N, 65°–75° W), where the wind seasonality and reversal at low levels are enhanced, allowing the inter-hemispheric moisture flux transport (cross-equatorial flow). Nevertheless, their convergence (AMJ and ON) is the crucial factor modulating the lowest isotopic values. Based on back trajectory analysis, the results demonstrated that moisture arrives from two primary sources: the Tropical North Atlantic (DJFM) and the Amazon Basin (JAS). A monthly δ 2H p and δ 18O p collection campaign was established in Central Ecuador ( n = 30) to complement stations biased towards the northern and southern parts. In contrast, higher values are found during DJF and JAS in a w-shaped pattern, suggesting a common regional controller. Nevertheless, stations along these regions show a similar intra-annual isotopic variability, with lower values during MAM and ON. At the same time, this complex orography creates diverse precipitation regimes (unimodal, bimodal, and three-modal) that make it difficult to establish a relationship with the local amount. The variability of the rainfall stable isotopic values (δ 2H p, δ 18O p) in the Ecuadorian Amazon to the Andes presents a marked local “altitude” effect.
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