Abstract: Based on the applicability analysis of the NCEP/NCAR reanalysis I data by the radiosonde data in the Three Rivers’ Headstream region and the adjacent regions, trends of water vapor transports in the Three Rivers’ Headstream region were analyzed by applying the daily wind and specific humidity of the reanalysis data during 1971-2010. The results show that the meridional water vapor input in the Three Rivers’ Headstream region decreased significantly, causing the net water vapor budget decreasing. The decadal variations of water vapor fluxes in the 1970s and 1980s were relatively weaker than those in the 1990s and 2000s. During 1971-2010, the water vapor budget showed an obvious decreasing trend in spring, summer and autumn, while no significant trend in winter. Overall, the water vapor transport into the region decreased significantly, especially in June and September during 1971-2010, which had adverse impacts on precipitation formation.

Key words: water vapor transport, water vapor budget, Three Rivers&, rsquo, Headstream region