Quantitative Identification of Moisture Sources over the Tibetan Plateau: Spatial Distributions and Temporal Variabilities

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Abstract The imbalanced hydrological cycles and water resource instability over the Tibetan Plateau (TP) are a topic of wide concern. Moisture sources affected by large-scale circulations are the main controls of precipitation and water resource distributions; as such, the quantitative identification of moisture sources is the key to the changes in precipitation or water-related environments, further aids efficient water management over the TP and in downstream regions of Asia. In this study, we primarily identified the spatial distributions and temporal variabilities of TP’s varied moisture sources, using HYSPLIT modeling and spatially dense precipitation isotopes (δ18O). Results showed that 1) moistures from the westerlies (West), the western arm of Indian summer monsoon (ISM) (ISM1), the eastern arm of ISM (ISM2), and the inner TP are the TP’s main moisture sources, with highest proportional contributions being >70%, ∼40%, >80%, and ∼10%–20% at northwest, southwest, and southeast sectors of the study area and the central TP region; 2) each moisture has its own region where it predominates and shows specific trends during 1951–2020 (West-northwest sector-increase, ISM1-southwest sector-increase, ISM2-southeast sector-decrease, and TP-central TP region-increase); 3) each of the moisture proportions and their temporal trends varied with different days of back trajectories (days 02–04–06–08–10), while their spatial patterns are similar; and 4) when verifying the modeled moisture proportions, precipitation δ18O is positively correlated or covaries with dry sources such as the West or TP moisture and inversely for humid ISM (ISM1 or ISM2) moisture. This work will improve our understanding of moisture-related hydrological, meteorological, and ecological studies in the “Asian Water Tower” region. Significance Statement The Tibetan Plateau (TP) is undergoing imbalanced hydrological cycles and water resource instability in response to global climate change. As the TP supplies vast quantities of water to Asia’s huge population, the socioeconomic impact caused by these changes is considerable. This study aims to quantitatively identify the spatial distributions and temporal variabilities of varied moisture sources over the TP in recent decades, using high-resolution modeling and ground-based precipitation isotopes. Results show that each moisture has its own region where it predominates and shows specific trends during 1951–2020. These findings can help to explain precipitation patterns or water resource distributions and provide insights into efficient water management over the TP and in downstream regions of Asia.