Comparison of moisture sources of summer precipitation in 1998 and 2020 in the middle and lower reaches of Yangtze River basin

The persistent heavy precipitation during summer in 1998 and 2020 in the middle and lower reaches of the Yangtze River basin (MLYRB) caused the most influential floods in the region during recent 30 years. Previous studies paid lots of attention to those events by analysing the spatial-temporal distributions and the circulation backgrounds; however, the comparison of moisture contribution to summer precipitation in the MLYRB in 1998 and 2020 have rarely been well addressed. This study tracked the moisture sources of summer precipitation in 1998 and 2020 in the MLYRB based on an Eulerian moisture tracking model (WAM-2layers) forced with ERA5 dataset and explored the similarities and differences of moisture transport and moisture contribution during the two periods. Results showed that the moisture contribution to summer precipitation in the MLYRB mainly transported by the southwest monsoon system, with the major sources extended across the Indo-China Peninsula, the Bay of Bengal and the Arabian Sea, to the south Indian Ocean. During the summer of 1998 and 2020, increased moisture contributions were mainly from the southwestern sources, particularly the Indo-China Peninsula and its surroundings. Meanwhile, decreased moisture contributions were found from the local recycling and the northeastern sources. In comparison with summer 1998, there were less moisture can be transported from the low-latitude oceans (particularly the Arabian Sea and the Bay of Bengal) to the MLYRB during summer 2020, except for the Northwestern Pacific.