Analysis of Heavy Precipitation and its Typical Weather Patterns over the Upper Reaches of the Yellow River

The frequency of disasters induced by heavy precipitation (HP) in the upper reaches of the Yellow River Basin (URYR) has increased notably. This study had further elucidated the structure and interactions of synoptic systems across different pressure levels and quantitatively characterized the anomalous driving factors. Four weather types had been identified: Xinjiang Trough (Type1, constituting 35% of HP), Mongolian Trough (Type2, 14%), Westward–Extension Western Pacific Subtropical High (WPSH) (Type3, 43%), and Cut–Off Cyclone (Type4, 8%). Influenced by the troughs, the moisture anomalies are transported by the southwesterly jet originating from Bay of Bengal low-pressure systems; mesoscale cyclones are positioned on the northwestern and northeastern margins of the URYR, respectively. In Type3, the WPSH and South Asian High demonstrate the greatest zonal expansion and central intensity (reaching 12610 gpm); the core of the mesoscale cyclone anomaly is situated in the central-northern segment distinguished by maximal moisture and energy, exhibiting the most pronounced extreme properties. The most notable characteristic of Type 4 is its stability and persistence presented the most favorable dynamic conditions, despite occurring with the lowest frequency. Moisture condition may play a more important role than dynamic in precipitation intensities over the URYR. Due to the anomalous evolution of atmospheric circulation, the anomalies in potential vorticity, vertical velocity, and moisture flux divergence vary at corresponding rates per 6-hour interval, and exhibit rapid fluctuations within 12 to 6 hours before HP. The positions of mesoscale systems and high precipitable water vaper show a correlation with the locations where HR events were recorded. The meridional moisture advection and meridional moist enthalpy serve as dominant mechanisms driving HP. These findings may offer a scientific basis for the prediction of HP events in the region.