Moisture sources and paths associated with warm-season precipitation over the Sichuan Basin in southwestern China: Climatology and interannual variability

Abstract

This study used the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model to examine the moisture sources and pathways associated with warm-season precipitation over the Sichuan Basin (SCB), southwestern China, with emphasis on the long-term mean state and interannual variability. Four groups of moisture pathways were identified over the period 1981–2017; i.e., the southwesterly, northeasterly, northwesterly, and westerly paths. With respect to the long-term mean state, the southwesterly path made the largest moisture contribution (36.0%) and, in combination with the northeasterly path (the importance of which has received little attention in previous studies), provided 70.2% of the total moisture. The Indian Ocean serves as the most important moisture source, accounting for 36.3% of the total moisture. In terms of interannual variability, compared with dry years, in wet years, the moisture contributions from the southwesterly path and the Indian Ocean increase by 18.6% (38.3% vs. 32.3%) and 20.71% (38.38% vs. 31.80%), but the contributions from the other moisture pathways and other major sources decrease. During the dry years, the northeasterly path, rather than the southwesterly path, provides the most moisture (34.6%). There are significant positive correlations between variations in runoff over the central and northern SCB and the moisture contribution from the Indian Ocean, which is associated with anomalous precipitation patterns over the SCB induced by fluctuations in the moisture contributions from the Indian Ocean.