Water Vapor Transport and its Influence on Water Stable Isotope in Dongting Lake Basin

Abstract. Understanding water vapor sources and transport paths is essential for assessing the water cycle and predicting precipitation accurately. Utilizing water vapor diagnosis and calculations, this study determined the water vapor sources and transport paths leading to precipitation in the Dongting Lake Basin in four seasons (represented by January, April, June, and October). In January, the water vapor generating precipitation originated from the Arabian Peninsula, driven by the southern branch of the westerlies over the southern side of the Tibetan Plateau, along the northern side of the Indian Peninsula through southwest China to reach the Dongting Lake Basin. In April, two transport paths emerged: one aligned closely with the January transport path but the location shifted slightly northward by one degree of latitude, and another was driven by the weak subtropical high over the southwestern Pacific, bringing moist air from the western Pacific via the South China Sea and Indochinese Peninsula. In June, the Dongting precipitation sourced from the northern branch of the South Indian Ocean subtropical high, crossed the equator and transported through various water bodies to southwestern China, finally reaching the basin. October saw a water vapor transport path from the western Pacific, crossing the South China Sea, and entering the Dongting Lake Basin influenced by the East Asian monsoon system. In different seasons, the variations in water stable isotopes along water vapor transport paths adhered to Rayleigh fractionation and water balance principles. These findings highlight the impact of atmospheric circulation on precipitation and isotopes, providing a framework for understanding water vapor isotope mechanisms and reconstructing past atmospheric conditions.