Influence of moisture transport on stable isotope in precipitation in Yarlungzangbo River basin

Abstract

The relationship between the variation of δ 18O in precipitation in Yarlungzangbo River basin and the moisture flux was analyzed with NCEP/NCAR reanalysis grid data and δ 18O in precipitation at four stations (Lazi, Nugesha, Yangcun and Nuxia) of the region investigated. In terms of spatial variations, there is obviously a positive correlation between them for the entire basin. With the decrease in moisture flux from the downstream to the upstream area, δ 18O in precipitation became gradually decreased. However, in terms of temporal variations, higher δ 18O in precipitation during spring is linked to small moisture flux while low δ 18O in precipitation during summer is linked to large moisture flux. A model involving meteorological data from NCEP/NCAR was subsequently set up which successfully traced the moisture transport trajectories at Yangcun station. Based on the traced moisture transport trajectories and the δ 18O in precipitation at Yangcun station, the relationship between δ18O in precipitation in Yarlungzangbo River basin and the moisture transport history was discussed. We found that the humid marine air mass from the Indian Ocean in general has significantly lower δ 18O values than the continental air mass from the north or local re-evaporation. The fluctuation of δ 18O in precipitation during the monsoon season is very pronounced; the lower values are usually related to farther distance and multilayer moisture transport, as well as moisture crossing the Himalaya Mountains.