Rainwater Isotopic Composition in the Ecuadorian Andes and Amazon Reflects Cross-Equatorial Flow Seasonality

• Published in: Water
• Main Authors: Danny Vargas, Oscar Chimborazo, Elemér László, Marjan Temovski, László Palcsu
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: cross-equatorial flow; stable isotopes; V-Index; low-level jet; precipitation; aerial lake; Hydraulic engineering; TC1-978; Water supply for domestic and industrial purposes; TD201-500; North Atlantic
• Online Access: https://doi.org/10.3390/w14132121; https://doaj.org/article/0f9db46c8df24ed48077db039d1e436d

The variability of the rainfall stable isotopic values (δ 2 H p, δ 18 O p ) in the Ecuadorian Amazon to the Andes presents a marked local “altitude” effect. 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. Nevertheless, stations along these regions show a similar intra-annual isotopic variability, with lower values during MAM and ON. In contrast, higher values are found during DJF and JAS in a w-shaped pattern, suggesting a common regional controller. A monthly δ 2 H p and δ 18 O p collection campaign was established in Central Ecuador ( n = 30) to complement stations biased towards the northern and southern parts. 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). Nevertheless, their convergence (AMJ and ON) is the crucial factor modulating the lowest isotopic values. 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). We propose that the amount of rainfall located at the V-Index region is a more robust approach for explaining the δ 2 H p and δ 18 O p variability rather than the local amount.