Moisture recycling modulates stable isotopes of river water in the Tibetan Plateau: Implications for paleo-elevation reconstruction

The isotopic lapse rate plays an important role in paleo-elevation reconstruction. However, there is a lack of a well-defined isotopic lapse rate of river water in the northeastern Tibetan Plateau, limiting the ability of reconstructing the paleo-elevation in the northeastern Tibetan Plateau. To address this knowledge gap, we collected and analyzed stable isotopes of river water in the Bailong River catchment. The δ 18 O and δD of river water ranged from −13.2 to −8.6 ‰ and −88.0 to −56.7 ‰, respectively. The effect of sub-cloud evaporation on precipitation in low elevation is stronger than that in high elevation based on the meteorological data. Combined with the spatial variations of sub-cloud evaporation effect on precipitation, melting water recharge and evaporation significantly influence the distribution of stable isotopes of river water within the Bailong River catchment. Notably, the δ 18 O lapse rate of the Bailong River catchment is 1.4 ‰/km, which is much lower than that of other rivers in the eastern Tibetan Plateau. Moreover, the isotopic lapse rate of river water in the eastern Tibetan Plateau gradually decreases with increasing latitude, which is attributed to the contribution of evapotranspiration to precipitation. As an important hydrological process, moisture recycling significantly plays a crucial role in shaping the isotopic compositions of precipitation and thereby affects the isotopic lapse rate. The atmospheric circulation patterns over the Tibetan Plateau are changing due to global warming, which further influences isotopic lapse rates. Therefore, it is urgent to assess the extent to which changes in the source of water vapor driven by global warming have impacted isotopic lapse rate.