Application of Stable Isotopic Compositions of Rainfall Runoff for Evaporation Estimation in Thailand Mekong River Basin

Abstract

The Mekong River Basin comprises approximately 38% of Southeast Asia. Our study area comprises the right-bank tributaries, which drain a substantial portion of Northeast Thailand. This study aimed to estimate the evaporative losses from streams during the 2013–2015 period. The normal and warm El Niño–Southern Oscillation (ENSO) phases caused higher temperatures and low rainfall in the 2014–2015 period. The results show that the local meteoric water line for precipitation isotopes had seasonal variation due to variable precipitation. The enrichment of river isotopes indicated that streams lost an average of 4% of their water through evaporation. During the cooling ENSO phase, significant evaporation occurs due to the deep convection that typically occurs in tropical regions. In contrast, evaporation was low during the warm ENSO phase because of its geographic location. The El Niño year’s isotope values were significantly more enriched than the La Niña year’s, showing that precipitation and positive temperature anomalies affected the isotopic compositions in the continental basin. Furthermore, the deuterium excess helped distinguish the relative contributions of the wet and dry seasonal sources to the moisture origin, indicating that the predominant source of moisture is inland evaporation, with a small contribution from the ocean.

Innovative Assessment of Mun River Flow Components through ANN and Isotopic End-Member Mixing Analysis

“…This depletion is generally attributed to the evaporative enrichment of heavy isotopes in open water bodies, which results in higher δ 18 O and δ 2 H values in river water compared to precipitation. The mean δ 18 O values in river water for the entire period studied across the UMR, CR, and MR locations indicate this enrichment, alongside variations in d-excess that underscore the differences in evaporation rates and moisture mixing processes between the river and atmospheric water [11,35,44].…”

“…The CR and MR also show differences in their seasonal isotopic values, with generally more depleted δ 18 O and δ 2 H values during the wet season, indicative of enhanced precipitation input and potentially reduced evaporation. However, the extent of seasonal variation in d-excess across these locations further points to the differential impact of evaporation and moisture source dynamics within the basin [35,54].…”

“…Both basins are surrounded by significant mountain ranges that play a crucial role in their hydrology. The Chi River Basin is bordered by the Dong Phaya Yen, Phetchabun, and Phu Phan mountain ranges, with elevations ranging from 300 to 1,300 meters, contributing to its complex river system [35]. In contrast, the Mun River Basin features the Banthat and Phanom Dong Rak mountains, with the landscape transitioning from elevated plateaus over 1,350 meters above sea level to lower plains towards the Mun River, indicating a varied topography from approximately 100 to 1,350 meters above sea level (Figure 1).…”

Groundwater Quality Variations in Multiple Aquifers: A Comprehensive Evaluation for Public Health and Agricultural Use

“…However, it is important to note that these observations are general, and specific geological factors, hydrological conditions, and human interventions can greatly influence groundwater levels [37]. Differences in extraction rates, aquifer characteristics (permeability and porosity), and rainfall patterns and evaporation can contribute to variations in groundwater depths between aquifers [56].…”

The estimation of young water fraction based on isotopic signals: challenges and recommendations

“…The time water takes to travel through a catchment, from inputting as precipitation to reaching the outlet, is an important indicator to characterize the catchment hydrology and determine the sensitivity of the catchment to pollutants (Sprenger et al, 2019). Since the migration, transformation, and phase change of water are accompanied by the transport, mixing, and fractionation of hydrogen and oxygen stable isotopes (i.e., 18 O and 2 H), these isotopes are widely used to perform hydrological and meteorological analyses at different scales, such as the identification of water vapor sources and transport patterns, the quantification of the contribution of end members to runoff, and the evaluation of water interactions and estimation of evaporation losses (e.g., Chen et al, 2015;Xia et al 10.3389/fevo.2023.1114259 Frontiers in Ecology and Evolution 02 frontiersin.org Eissa et al, 2016Eissa et al, , 2018Zuecco et al, 2019;Laonamsai et al, 2021Laonamsai et al, , 2022Wang et al, 2022). During the process of runoff generation in rainfall-dominated catchments, the isotopic signal in precipitation is usually dampened when it is transmitted to river water, due to the buffering effect of the catchment and its mixing with groundwater and soil water with relatively constant isotopic signals.…”