Application of Lagrange Water Vapor Source Diagnosis Method to the Three-river Source Area

The Three-river Source (TRS) region locating at the Tibet Plateau hinterland, contains a huge resources, gives birth to several world famous rivers, and supplies fresh water resources for East Asia. Identification of the regional moisture source is of great significance for understanding of regional water budget and improving the ability of water resources management. Ensemble modeling method is used with the three-dimensional Lagrangian transport model FLEXPART (Flexible Particle Model), driven by the GFS (Global Forecast System) reanalysis data (four times one day) from NCEP/NCAR. Then, the water vapor transport and source identification technology is used to identify the main moisture source for TRS region, with consideration of the spesific humidity changes along their transport pathways. The result indicates that a large number of air parcels experience several surface-atmosphere water vapor cycle process before reaching the TRS region. Dominated by the moisture transport form the prevailing westerlies and the central Asia strong evaporation, moisture sources characterized by relative short time transport (less than 6 days) mainly come from the Tibetan Plateau and its northwest edge, while the moisture sources with longer time (8-10 days) can be traced backward to the Arabian Sea, the Bay of Bengal, and so on. The water vapor reaching the TRS region transport can roughly be categorized to two pathways: The first is along the Somali to the Arabian Sea water vapor transport across the equator, and the second is the west path controlled by the west wind, transport from central Asia and west Asia to TRS region. Quantitative analysis shows that the moisture source also exhibits obvious sub-seasonal variability during the summer, characterized by the leading source area located in the west side of TRS region in June, and the Arabian Sea in July. However, the contribution from the Arabian Sea decreases and the contribution from the Bay of Bengal increases in August. Throughout the summer, the North of the Plateau maintains a stable water vapor transport.