Bay of Bengal cyclones fuel non-monsoon extreme precipitation on the central Tibetan Plateau

Abstract

Extreme precipitation on the central Tibetan Plateau, particularly outside the summer monsoon season, strongly affects glacier mass balance and downstream water availability, yet the moisture transport mechanisms remain poorly understood. This study combines high-resolution measurements of the isotopic composition of atmospheric water vapour at Nam Co Lake with isotope-enabled climate model simulations to investigate an extreme snowfall event on 25 October 2022. We show that the event was triggered by a cyclonic disturbance over the northern Bay of Bengal, reinforced by the western Pacific subtropical high, which channelled moisture into the plateau interior. We identify a growing class of similar cyclone-driven extreme precipitation events before and after the monsoon season from 1990 to 2022. Climate projections indicate that such events will become more frequent under moderate and high emissions. These findings identify a robust isotopic fingerprint of cyclone–orography interactions and highlight the growing role of Bay of Bengal moisture in Tibetan Plateau water security in a warming climate. Extreme precipitation events on the central Tibetan Plateau outside the monsoon season have been increasingly linked to cyclones in the Bay of Bengal and is projected to occur more frequently under global warming, as suggested by observations and model experiments.