Journal
HYDROLOGICAL PROCESSES
Volume 33, Issue 23, Pages 2997-3009Publisher
WILEY
DOI: 10.1002/hyp.13541
Keywords
back trajectory; isotopes; Qinghai Lake watershed; reevaporation; Tibetan Plateau; water vapour
Categories
Funding
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University [2018-KF-03]
- Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences [NIGLAS2017GH07]
- National Natural Science Foundation of China [41701036, 41730854, 41861022]
- Key Laboratory of Watershed Geographic Sciences, Chinese Academy of Sciences [WSGS2017006]
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Stable water isotopes (delta O-18 and delta H-2) are an important source signature for understanding the hydrological cycle and altered climate regimes. However, the mechanisms underlying atmospheric water vapour isotopes in the northeast Qinghai-Tibetan Plateau of central Asia remain poorly understood. This study initially investigated water vapour isotopic composition and its controls during the premonsoon and monsoon seasons. Isotopic compositions of water vapour and precipitation exhibited high variability across seasons, with the most negative average delta O-18 values of precipitation and the most positive delta O-18 values of water vapour found during the premonsoon periods. Temperature effect was significant during the premonsoon period but not the monsoon period. Both a higher slope and intercept of the local meteoric water line were found during the monsoon period as compared with in the premonsoon period, suggesting that raindrops have been experienced a greater kinetic fractionation process such as reevaporation below the cloud during the premonsoon periods. The delta H-2 and delta O-18 signatures in atmospheric water vapour tended to be depleted with the occurrence of precipitation events especially during the monsoon period and probably as a result of rainout processes. The monthly average contribution of evaporation from the lake to local precipitation was 35.2%. High d-excess values of water vapour were influenced by the high proportion of local moisture mixing, as indicated by the gradually increasing relative humidity along westerly and Asian monsoon trajectories. The daily observation (observed epsilon) showed deviations from the equilibrium fractionation factors (calculated epsilon), implying that raindrops experienced substantial evaporative enrichment during their descent. The average fraction of raindrops reevaporation was estimated to be 16.4 +/- 12.9%. These findings provide useful insights for understanding the interaction between water vapour and precipitation, moisture sources, and help in reconstructing the paleoclimate in the alpine regions.
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