Characteristic analysis of water vapor variation using GNSS tomography during the 2023 typhoon-induced rainstorm in Jingjinji area, China

Induced by Super Typhoon Doksuri and Khanun, an extreme rainstorm hit the Beijing, Tianjin, and Hebei province (Jingjinji area) of China in 2023, causing severe damage and losses. To comprehensively understand the mechanism of water vapor supply, this study applied the Global Navigation Satellite System (GNSS) tomography technique to retrieve three-dimensional (3D) water vapor fields during the rainstorm. After ensuring the feasibility of GNSS-derived water vapor field, the characteristics of water vapor during the rainstorm were analyzed with rainfall record and regional topography. Integrated water vapor (IWV) from GNSS tomographic results was first investigated. Temporal analysis at four selected GNSS station indicates that the IWV fluctuated and rose before the heavy rainfall occurred, and kept at a high level during the rainstorm. This was primarily due to the persistent transport of water vapor from the ocean surface through the warm and moist airflow caused by two typhoons. Combining analysis with the spatial distribution of IWV and topography, the transported water vapor converged in the central and southern parts of Jingjinji area due to the obstructions of Yanshan Mountains in the north and Taihang Mountains in the east. The falling area of this rainstorm coincided with water vapor convergence zone, demonstrating the potential of GNSS technique for rainstorm diagnosis. Besides, 3D water vapor variation was also investigated with regional topography. Horizontal distribution of water vapor density (WVD) at representative levels evidently exhibited the water vapor convergence through transportation of typhoon and obstruction of terrain. Moreover, profiles about WVD and vertical velocity in both latitude and longitude directions were analyzed. Vertical water vapor variation was in accordance with vertical velocity, indicating that the concentration process of water vapor due to topography can be captured by GNSS tomography. In general, GNSS tomography is a useful technique for clearly exhibiting water vapor variation in multi-dimensions. This is particularly important for monitoring severe rainstorms which are significantly influenced by topography.