Roles of oceanic moisture exports in modulating summer rainfall over the middle‐lower Yangtze River Basin: Inter‐annual variability and decadal transition

Abstract

AbstractPrecipitation over the mid‐lower reaches of the Yangtze River Basin (YRB), which is a typical East Asian monsoon region in China, is strongly impacted by oceanic moisture exports (OMEs) and features variability at multiple spatial‐temporal scales, resulting in frequent floods and droughts. We focus on two key issues of OME and its relevance to the summer rainfall variability over the YRB: determination of the individual contributions of OME from three specific oceanic sub‐regions: the Arabian Sea (ARS), Bay of Bengal (BOB), and South China Sea (SCS), and their roles in the inter‐annual variability and decadal changes in YRB summer rainfall. Using a Lagrangian forward trajectories tracing approach, we create a catalogue of OME‐based diagnosed precipitation fields for three sub‐regions spanning the summer seasons (May to August) of 1980–2013 with 6‐hourly resolution using ERA‐Interim data. The results show that the pattern of the diagnosed OME‐based precipitation resembles the observed pattern over the YRB in terms of climatology and temporal variation. Climatologically, the SCS region accounts for the largest relative contribution (60.7%), followed by the ARS (30.8%), whereas the contributions of the BOB (8.5%) are almost negligible. On the inter‐annual scale, the variation in OME‐based rainfall originated from the ARS, and the BOB is out of phase with that of the SCS. In contrast to climatology, the inter‐annual changes in rainfall over the YRB are primarily modulated by the variation in the OME from the ARS. However, for the decadal changes, particularly in 1992/1993 over the YRB, the SCS and ARS are equivalent contributors to the summer precipitation over the YRB. These findings thus provide new insights into our understanding of the multi‐scale variability of summer precipitation over the YRB region.