The Water Vapor Origin of a Rainstorm Event in the Taklamakan Desert

In July 2021, the Taklamakan Desert (TD) experienced an unprecedented rainstorm with daily precipitation exceeding 61.1 mm, triggering mudslides and landslides, highlighting the increasing frequency of extreme precipitation events even in arid regions under global warming. The water vapor sources and transport paths of this rainstorm are still puzzling due to the insufficient representation of physical processes in previous analytical models, leading to possible deviations from reality. Here, using the online Eulerian Weather Research and Forecasting model with water vapor tracer (WRF-WVT), we aim for an improved understanding of water vapor sources of the rainfall event. Results demonstrate that the most important water source for this event is water vapor from local evapotranspiration, contributing to 32.77% of the rainstorm moisture. Water vapor from Upstream Westerlies (28.95%) and East Asian Drylands (28.54%) are transported over the precipitation area by the westerlies owing to the strong lower-level low-pressure system, being the second-most important precipitation source. These sources contribute significantly more than other regions, including the Arabian Sea (5.56%), the Tibetan Plateau (2.16%), and the South Asian Monsoon (0.77%). External moisture sources collectively provide over 65.98% of the precipitation, underscoring their important role. Notably, local evapotranspiration significantly influences precipitation, exceeding the contributions from other individual sources. By comparing with the 2016 precipitation event, it is found that a low-pressure trough extending southward to the west of the TD plays a significant role in the 2021 rainstorm event. The presence of the trough significantly enhances the moisture transport of the westerlies and the upward motion, contributing to the occurrence of extreme precipitation events.