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<p>In plateau climate, there will be obvious raindrop stable isotope ratio changes during falling process due to the influenced by the below-cloud evaporation. Quantitative assessment of this change is very important for clarifying the regional water cycle and improving precipitation forecast and water resources management under global warming. Based on the hierarchical hypothesis calculation scheme of the Stewart model together with the aerial detection data of seven meteorological stations in 2022, this study estimated the changes of hydrogen and oxygen stable isotopes of precipitation on the Gannan Plateau. The results show that isotope enrichment is obvious on the below-cloud evaporation from 14:00 to 18:00. The evaporation is more significant in summer than that in other seasons. The low altitude area in the eastern part of the study area (Zhuqu) is the most affected by sub-cloud evaporation, followed by the high altitude area in the central part (Maqu, Jone). The slope and intercept of meteoric water lines based on measured samples in the study area are lower than those of (Global Meteoric Water Line) GMWL. When the temperature is higher than 24℃, or the relative humidity is lower than 60%, the sub-cloud evaporation results in sizeable isotopic differences. When the remaining fraction of evaporation is greater than 95%, the linear index of residual evaporation fraction of raindrops&#xa0;and&#xa0;the change in precipitation surplus of deuterium is 1.12. When the temperature is high, the humidity is high, the precipitation is high, and the raindrop diameter is small, the secondary evaporation effect under the cloud is strong. If the cloud base is high, the homogenization hypothesis will overestimate the isotope change, and the stratification hypothesis can reflect the secondary evaporation effect more accurately. The results can provide references for short-term rainfall forecasts over the Gannan Plateau.</p>

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Below-cloud evaporation effect on stable isotopes on precipitation on the Gannan Plateau region based on Stewart model

  • 期刊论文

  • 发表日期：

    2025年1月9日

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  • Fenli Chen,
  • Huizhen Li,
  • Minyan Gao,
  • Nan Kang,
  • Qiuyan Zhang,
  • Yiwen Yao,
  • Xulin Li,
  • Tian Yin,
  • Shiyu Wang

摘要

In plateau climate, there will be obvious raindrop stable isotope ratio changes during falling process due to the influenced by the below-cloud evaporation. Quantitative assessment of this change is very important for clarifying the regional water cycle and improving precipitation forecast and water resources management under global warming. Based on the hierarchical hypothesis calculation scheme of the Stewart model together with the aerial detection data of seven meteorological stations in 2022, this study estimated the changes of hydrogen and oxygen stable isotopes of precipitation on the Gannan Plateau. The results show that isotope enrichment is obvious on the below-cloud evaporation from 14:00 to 18:00. The evaporation is more significant in summer than that in other seasons. The low altitude area in the eastern part of the study area (Zhuqu) is the most affected by sub-cloud evaporation, followed by the high altitude area in the central part (Maqu, Jone). The slope and intercept of meteoric water lines based on measured samples in the study area are lower than those of (Global Meteoric Water Line) GMWL. When the temperature is higher than 24℃, or the relative humidity is lower than 60%, the sub-cloud evaporation results in sizeable isotopic differences. When the remaining fraction of evaporation is greater than 95%, the linear index of residual evaporation fraction of raindrops and the change in precipitation surplus of deuterium is 1.12. When the temperature is high, the humidity is high, the precipitation is high, and the raindrop diameter is small, the secondary evaporation effect under the cloud is strong. If the cloud base is high, the homogenization hypothesis will overestimate the isotope change, and the stratification hypothesis can reflect the secondary evaporation effect more accurately. The results can provide references for short-term rainfall forecasts over the Gannan Plateau.