Group 1 - The current rainfall in multiple regions coincides with China's critical flood prevention period known as "July down, August up," which is characterized by complex and severe flood conditions each year [1] - The rainfall during this period mainly presents two forms: "frontal rainstorm" and "warm area convection" [3][5] - Frontal rainstorms occur when abundant moisture from the summer monsoon meets strong cold air, leading to intense and widespread rainfall [3] Group 2 - When the influence of cold air is weak or distant, the warm moist air accumulates in northern regions, creating a hot and humid environment, which can trigger small-scale strong convection [5] - The triggers for this convection include topographical uplift of warm moist air, sea-land breezes, and low-level jet streams, but this warm area convection typically does not result in regional heavy rainfall [5]