Revisiting Water Vapor Transport and Water Isotopes in the Dongting Lake Basin Across Two Centennial Extreme Events

Abstract. Water vapor source tracing of extreme weather events is essential for water vapor diagnosis, relating to accurate assessments of the water cycle and associated isotopic effects. Based on our prior climatic-scale study and using a consistent methodological framework, this study identifies the atmospheric circulation patterns and water vapor transport pathways for a once-in-a-century extreme rainstorm (June 2017) and freezing disaster (January 2008) events in the Dongting Lake Basin. Despite occurring in distinct seasons, both events exhibited remarkable similarities in circulation situation and water vapor transport: at low latitudes, a deepened South Branch Trough and westward-extended Western Pacific Subtropical High dominate warm, moist maritime air transported from low to high latitudes; at mid-to-high latitudes, a strong, stable Blocking High and East Asian Trough controlled the southward surge of cold air. The Dongting Lake Basin was situated within the saddle field where cold and warm air masses converge. Southwest transport contributed the largest water vapor share for both extreme events, setting historical records for their respective months. Constrained by relatively invariant atmospheric conditions, low-latitude oceanic vapor isotopes exhibited minor seasonal variation; however, because June precipitation significantly exceeded January amounts, June water vapor and resulting precipitation isotopes were substantially depleted relative to January values. Within frontal systems formed by strong cold-warm air interactions, temperature, humidity, wind direction, and speed varied considerably at different altitudes, as clearly reflected in water vapor transport differences at these representative vertical levels. Together, these two studies form a systematic understanding of climatic regularity to extreme-event behavior.