Group 1 - The main flood season in China varies by region, with the Northeast and North China experiencing it from July to August, while the Yangtze River basin has its peak from June to August, and South China from April to October [1][3][5][7] - The critical flood prevention period in North China and Northeast is from July 16 to August 15, known as "July down, August up," during which urban flooding and river dam risks are prevalent [3][5] - The Yangtze River basin experiences a "plum rain" period from late June to early July, characterized by continuous rain and high humidity, often accompanied by thunderstorms [5] Group 2 - Flood warning levels are categorized into two: warning water level and guarantee water level, which indicate the state of flood defense readiness [10] - The warning water level signifies a state of alert for flood defenses, while the guarantee water level represents the maximum water level that can be safely managed by flood defenses [12] - Floods are classified and numbered when they exceed historical records or reach significant scales that threaten local flood safety, prompting public awareness [13][15]