Moisture transport and sources of an extreme rainfall event of June 2021 in southern Xinjiang, China

Abstract

A highly extreme rainfall event occurred during June 15–17, 2021 (21·6 event) over southern Xinjiang (SXJ) of China, with daily rainfall overwhelming the climatological annual total at three national stations along the north of Kunlun Mountains. During this event, the SXJ is situated upstream of the 500 hPa trough line and close to the 200 hPa upper jet stream entrance, favouring the upper (lower) level divergence (convergence) with intensified ascending motions and prominent moisture convergence. We examined the moisture paths and sources for this significant rainfall event using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLT) model. The findings indicate that the majority of the moisture sources are located in areas west of the SXJ, extending from central Asia to the North Atlantic, whereas only a small number of trajectories originate from areas south or east of the SXJ. Seven relevant moisture sources for the rainfall event have been divided. About 80.0% of the total moisture is contributed by central Asia, which ranks top in terms of moisture contribution (∼33.2%), north Eurasia (∼25.7%), and water areas (∼17.7%), including the Mediterranean, Black and Caspian Sea region, while fractional moisture contributions among the other four regions are all below 8.0%. When compared to other parts of China (such as South China and East China), where southerly and/or easterly trajectories are the predominant moisture channels, the distribution patterns of moisture trajectories during this event are noticeably different.