2025-10-13 中国科学院（CAS）
＜関連情報＞
- https://english.cas.cn/newsroom/cas_media/202510/t20251014_1089402.shtml
- https://www.sciencedirect.com/science/article/pii/S0022169425016403
中央チベット高原タングラ山脈における12年間の観測で明らかになった雲下蒸発による降水中の安定同位体への影響 Effects of below‐cloud evaporation on stable isotopes in precipitation revealed by 12-year observations in the Tanggula Mountains, Central Tibetan Plateau
Xiaobo He, Shichang Kang, Shaoyong Wang, Yongjian Ding, Xiaoyi Shi, Fei Zhang, Zengcheng Jin
Journal of Hydrology Available online: 24 September 2025
DOI:https://doi.org/10.1016/j.jhydrol.2025.134300
Highlights
- The below-cloud evaporation was estimated using long-term observational data in the climatic transition zone of the TP.
- The estimated below-cloud evaporation showed a significant decreasing trend at the annual scale.
- The below-cloud evaporation of precipitation was notably weaker compared to surrounding regions of the TP.
- Relative humidity plays a dominant role in regulating below-cloud evaporation processes.
Abstract
Below-cloud evaporation of precipitation plays a crucial role in regional hydrological cycles and can effectively reflect the transitional climate characteristics. However, the below-cloud evaporation effect remains poorly quantified under current warming-wetting climate changes in the Tanggula Mountains, a typical climatic transition zone of the central Tibetan Plateau (TP); thus, its temporal trends and driving mechanisms remain poorly understood. Here, we combined long-term observations on precipitation stable isotopes and meteorological data with the Stewart model to estimate sub-cloud evaporation and determine its influence on precipitation isotopes in the Tanggula Mountains. The annual weighted mean of the remaining raindrop fraction was estimated at 88.1%, and a significant increasing trend was observed at the annual scale, which indicates a progressive weakening of the below-cloud evaporation intensity in this region. Significant isotope modifications in precipitation were observed during the descent from the cloud base to ground, with δ18O increasing by 2.6‰ and d-excess decreasing by 9.8‰. This indicated that below-cloud evaporation contributed to a noticeable enrichment of heavy stable isotope in precipitation in the central TP. For every 1% increase in the remaining raindrop fraction, the △δ18O value decreased by 0.2‰ and △d value increased by 0.63‰. However, the below-cloud evaporation of precipitation in the central TP was notably weaker than that of the regions surrounding the TP. This phenomenon can be attributed to the widespread presence of lakes and wetlands, influence of the Indian Summer Monsoon, and cold-wet island effects of the cryosphere in the central TP. These factors create distinct cold-humid climate conditions that effectively suppress below-cloud evaporation. The random forest model further demonstrated that relative humidity plays a dominant role in regulating below-cloud evaporation processes. Therefore, current climatic warming and wetting will likely further weaken the below-cloud evaporation of precipitation in the region. The findings of this study provide a critical scientific basis for paleoclimatic reconstruction and water resource management in the central TP.
