Moisture Sources and Pathways of Annual Maximum Precipitation in the Lancang-Mekong River Basin

Recent extremely heavy precipitation has led to substantial economic losses and affected millions of residences in the Lancang-Mekong River Basin (LMRB). This study analyzed the spatial-temporal characteristics of the annual maximum precipitation (R1X) of the LMRB and identified the moisture sources and pathways conducive to R1Xs using a Lagrangian back trajectory model. Results show that India Ocean and Bay of Bengal (IO/BOB), local evapotranspiration, and West Pacific Ocean and East China (WP/EC) are the three main moisture transport pathways of the R1Xs in LMRB, contributing 68.3%, 20.4% and 11.3% of the trajectories, respectively. R1Xs in the downstream eastern area are affected by tropical cyclones bringing large amounts of moisture from the WP/EC. As tropical cyclones shifted northward under climate change impact, more extreme precipitation occurred over the LMRB due to moisture coming from WP/EC, but those from the IO/BOB had decreased because of the slowdown of flows across the Equator. Recent extremely heavy precipitation has led to more frequent floods, storm surges, and other natural hazards in the Lancang-Mekong River Basin, resulting in substantial economic losses and affecting millions of residences. This study used annual maximum precipitation to represent the extreme precipitation and analyzed its spatial-temporal characteristics and the moisture sources and pathways. Results show that the extreme precipitation of the upstream region mainly occurred in July, while that of the downstream region mainly occurred in August-September. The moisture pathways of the historical extreme precipitation were identified using a physical-based model, and are classified into three clusters using a machine-learning model. West Pacific Ocean and East China, local evapotranspiration, and Indian Ocean and Bay of Bengal (IO/BOB) are the three moisture transport pathways with contributions of 68.3%, 20.4%, and 11.3% to the total pathways. The tropical cyclones bring large amounts of moisture and mainly affect R1Xs in the downstream eastern area. Tropical cyclones shifted northward under climate change impact, and more extreme precipitation occurred over the LMRB due to moisture coming from the West Pacific Ocean and East China, but those from the IO and BOB had decreased because of the slowdown of flows across the Equator. The timing of the annual maximum precipitation of the Lancang-Mekong River Basin (LMRB) varies from July to September The extreme precipitation of the LMRB mainly received moisture from the Indian Ocean to the West Pacific Ocean Tropical cyclones will bring more extreme precipitation to the LMRB under climate change