Monitoring Heavy Rainfall Events in East Asia Using High-Resolution Isotopic Observations

It is important to understand the mechanisms of heavy rainfall events, as such information could improve forecasting of these events and help mitigate their adverse impacts on life and property. In this study, we analyzed hourly stable isotopic compositions in water vapor (δ¹⁸O_v and d-excess_v) during heavy rainfall events in the summer monsoon season (June to September) from 2013 to 2023 in Nanjing, eastern China. These data were extracted from the longest data set of high-resolution and continuous in situ observations of water vapor isotopes globally. Based on these data, we identified four evolution patterns of δ¹⁸O_v during heavy rainfall events, corresponding to different weather systems: slow-declining (tropical cyclone interacting with mid- and high-latitude system), W-shaped (tropical cyclone), U-shaped (cold vortex system), and inclined L-shaped (upper-level trough system). The isotopic variations suggest that heavy rainfall events in eastern China were mainly sustained by moisture from adjacent oceans (including the South China Sea and the East China Sea) and terrestrial environment rather than from the distant Indian Ocean as previously suggested. In addition, for some heavy rainfall events with an intermittent period, the nearby oceanic moisture transport alters before and after the intermittent period due to an intensity change or overall transition of low-level weather systems. This study serves as a benchmark for tracing heavy rainfall processes in East Asia using high-resolution water vapor isotopes.