The altitude effect of δ 18O in precipitation and river water in the Southern Himalayas

Abstract

The lapse rate of water isotopes is used in the study of the hydrologic cycle as well as in the estimation of uplift of the Tibetan Plateau. The greater elevation contrast in the Southern Himalayas allows for a detailed discussion about this lapse rate. We analyze variations of δ 18O in precipitation and river water between 1320 m and 6700 m elevations in the Southern Himalayas, and calculate the specific lapse rate of water δ 18O. The results show that the multi-year average lapse rate in precipitation over this region is 0.15‰/100 m. The one-year average lapse rate is 0.17‰/100 m from three sites along the Southern Himalayas. The two results agree, but are much lower than the global average of 0.28‰/100 m. This work also shows that there is a difference in precipitation δ 18O lapse rate between the monsoon and non-monsoon seasons. The calculated precipitation lapse rate is much lower than that in surface water.