Analyze on the contribution of the moisture sources to the precipitation over mid-low Lancang River nearby region and its variability in the beginning of wet season

Based on reanalysis data from 1979 to 2015, an airflow trajectory model, Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT), is employed to estimate the moisture sources feature and its relationship with the mid-low Lancang River nearby region (LR) precipitation in wet season. The results reveal that the main sources of moisture over LR originate from the Indian Ocean, Western Pacific Ocean (WP), Eurasia continent, North Africa, and North Atlantic Ocean. Detailed analysis indicates that although the largest moisture over LR is sourced from the Indian Ocean, the moisture sourced from WP takes a more important role for LR precipitation variability. It is found that the typical dry/wet years in May (a transition month in the beginning of wet season) precipitation over the LR matches well with the decreasing/increasing of moisture sourced from WP, which indicates that the interannual variability of May precipitation over the LR is significantly modulated by the contributions of the moisture sourced from WP. A similar relationship was found for the precipitation over LR in May and the moisture contributions sourced from WP on decadal time scale. There is a transfer around 1997 from a drier May period (1979-1997) into a wetter May period (1998-2009), which is consistent with the change of the moisture contribution sourced from WP. Further, it is worth noticing that the significant downward trend of May precipitation over LR since the twenty-first century is consistent with the decreasing trend of moisture contribution sourced from WP, highlighting the dominant role of the moisture sourced from WP for the LR precipitation in May.