The Altitude Effect of Stable Isotopes in Rivers Over the Tibetan Plateau

Abstract

Abstract The altitude effect of stable isotopes in river water is key to paleoelevation reconstruction, yet remains poorly quantified at regional scales due to monitoring challenges. This study compiled river water isotope data across the Tibetan Plateau and used a decision‐tree‐based random forest model to simulate high‐resolution δ 18 O patterns. We produced the first systematic, spatially explicit map of the δ 18 O altitude effect over the entire plateau, revealing strong spatial heterogeneity. Results show that δ 18 O exhibits a “low in the south, high in the north” pattern driven by atmospheric circulation, while d‐excess displays a “low in the west, high in the east” trend controlled by sub‐cloud evaporation. The steepest altitudinal gradient occurs on the southern slope. This spatial heterogeneity is jointly regulated by moisture sources and sub‐cloud evaporation processes. The findings clarify the applicability and limitations of river water isotopes for paleoelevation studies on the Tibetan Plateau.