Atmospheric humidity
; Atmospheric thermodynamics
; Factor analysis
; Isotopes
; Linear regression
; Rain
; Trajectories
; Water piping systems
; Air mass trajectories
; Fractionation process
; Isotopic composition
; Meteoric water lines
; Multiple linear regressions
; Quantitative estimates
; Stable isotopic compositions
; Statistical approach
; Precipitation (meteorology)
; air mass
; environmental factor
; fractionation
; hydrological modeling
; isotopic composition
; meteoric water
; monsoon
; precipitation (climatology)
; precipitation quality
; rainfall
; stable isotope
; statistical analysis
; Indochina
; Mekong Delta
; Viet Nam
英文摘要:
This study analyzes the influence of local and regional climatic factors on the stable isotopic composition of rainfall in the Vietnamese Mekong Delta (VMD) as part of the Asian monsoon region. It is based on 1.5 years of weekly rainfall samples. In the first step, the isotopic composition of the samples is analyzed by local meteoric water lines (LMWLs) and single-factor linear correlations. Additionally, the contribution of several regional and local factors is quantified by multiple linear regression (MLR) of all possible factor combinations and by relative importance analysis. This approach is novel for the interpretation of isotopic records and enables an objective quantification of the explained variance in isotopic records for individual factors. In this study, the local factors are extracted from local climate records, while the regional factors are derived from atmospheric backward trajectories of water particles. The regional factors, i.e., precipitation, temperature, relative humidity and the length of backward trajectories, are combined with equivalent local climatic parameters to explain the response variables d18O, d2H, and d-excess of precipitation at the station of measurement.
The results indicate that (i) MLR can better explain the isotopic variation in precipitation (R2ĝ€ Combining double low line ĝ€0.8) compared to single-factor linear regression (R2ĝ€ Combining double low line ĝ€0.3); (ii) the isotopic variation in precipitation is controlled dominantly by regional moisture regimes (ĝ1/4 70ĝ€%) compared to local climatic conditions (ĝ1/4 30ĝ€%); (iii) the most important climatic parameter during the rainy season is the precipitation amount along the trajectories of air mass movement; (iv) the influence of local precipitation amount and temperature is not significant during the rainy season, unlike the regional precipitation amount effect; (v) secondary fractionation processes (e.g., sub-cloud evaporation) can be identified through the d-excess and take place mainly in the dry season, either locally for d18O and d2H, or along the air mass trajectories for d-excess. The analysis shows that regional and local factors vary in importance over the seasons and that the source regions and transport pathways, and particularly the climatic conditions along the pathways, have a large influence on the isotopic composition of rainfall. Although the general results have been reported qualitatively in previous studies (proving the validity of the approach), the proposed method provides quantitative estimates of the controlling factors, both for the whole data set and for distinct seasons. Therefore, it is argued that the approach constitutes an advancement in the statistical analysis of isotopic records in rainfall that can supplement or precede more complex studies utilizing atmospheric models. Due to its relative simplicity, the method can be easily transferred to other regions, or extended with other factors.
GFZ German Research Centre for Geosciences, Section 5.4 Hydrology, Potsdam, Germany; SIWRR Southern Institute of Water Resources Research, Ho Chi Minh, Viet Nam; Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Potsdam, Germany; University Potsdam, Institute of Earth and Environmental Science, Potsdam, Germany
Recommended Citation:
Le Duy N,, Heidbüchel I,, Meyer H,et al. What controls the stable isotope composition of precipitation in the mekong delta? A model-based statistical approach[J]. Hydrology and Earth System Sciences,2018-01-01,22(2)