Spatiotemporal characteristics of summer extreme precipitation over the Inner Tibetan Plateau in recent decades

The Inner Tibetan Plateau (ITP), serving as a critical component of the Asian hydrological circulation, has witnessed an increase in summer extreme precipitation events under global warming. However, the spatiotemporal characteristics and underlying mechanisms of the events remain insufficiently understood. This study identifies two distinct synoptic patterns that govern summer regional extreme precipitation events (REPEs) over the ITP from 1979 to 2020. The first pattern (REPE1, constituting 50.5% of the events) is characterized by a Rossby wave train inducing a negative-positive-negative geopotential height anomaly, accompanied by moisture convergence via southwesterlies and convective updrafts over the southeastern ITP. Conversely, the second pattern (REPE2, 49.5%) features a persistent positive-negative-positive geopotential height anomaly associated with mid-to-high latitude circulation, along with moisture convergence driven by southeasterlies and ascending motions over the southwestern ITP. Moreover, both REPE1 and REPE2 have exhibited increased frequencies post-2010, with REPE2 showing a more pronounced upward trend. The rising frequencies of REPE1 and REPE2 have contributed significantly to the increase in extreme precipitation over the ITP in recent decades.