Spatiotemporal structure of the moisture sources feeding heavy precipitation events over the Sichuan Basin

Abstract

ABSTRACTThe Sichuan Basin (SCB), in southwest China, is characterized by a high frequency of heavy precipitation (HP) events in the boreal summer. In this study, the top 50 HP events that occurred in the SCB were selected, based on daily precipitation gauge data during 1980–2013, and the moisture sources for these events have been identified. Taking advantage of the Lagrangian approach, we particularly examined the spatiotemporal structure of the moisture sources, both in their magnitude and temporal sequence. The results of this study can be summarized as follows: (1) the quantification of the contribution of the moisture sources indicated that the remote sources of moisture originating from the Tibetan Plateau, Indian Peninsula, Bay of Bengal and the Arabian Sea made considerable contributions to the moisture in the HP events; however, these areas were only the third most important factor in climatology, following the stronger influence of moisture uptake from the SCB local regions and the nearby Indo‐China Peninsula and South China Sea regions; (2) the time that moisture involved in the HP events varies between a few hours to more than a week before the HP events. Most of the moisture uptakes happened 1–5 days before the events, with maximum uptake occurring about 1 day before; (3) individual event‐to‐event variability of moisture sources was apparent. However, in contrast to the primary moisture contributors, this event‐to‐event variation depended largely on the externally imported moisture, particularly water vapor conveyed by both dominant southwest circulations and the moisture exported from the Tibetan Plateau, rather than the local SCB region. These results have established the atmospheric flow patterns that are prerequisites for HP events; meanwhile, regional moisture availability over the SCB region could also be an essential component of forecasting the HP events and needs to be better understood.