Rapid Increase in Extreme Hourly Precipitation in Recent Two Decades in the Tibetan Plateau and Its Large-Scale Drivers

Although extreme hourly precipitation (EHP) over the Tibetan Plateau (TP) has received growing attention, its spatiotemporal variability and the underlying mechanisms governing regional responses remain unclear. This study explores the spatiotemporal characteristics of EHP over its eastern edge during the summers of 1988–2023. A trend reversal is identified: the amount, intensity and frequency of EHP all decreased during 1988–2003 but increased in 2004–2023, with the amount and frequency exhibiting significant rapid growth. These changes are linked to the co-evolution of the South Asian High (SAH) and Western Pacific Subtropical High (WPSH). Their joint expansion enhances EHP via favorable dynamical and thermodynamic configurations, including intensified upper-level divergence, lower-level convergence, deep ascending motion, convective instability, 500 hPa specific humidity, and moisture flux convergence. Spatially, SAH expansion primarily promotes EHP over the northeastern TP via thermodynamic processes, whereas WPSH expansion mainly intensifies EHP over the southeastern TP through dynamical forcing.