Core Viewpoint - The article discusses the correlation between urban work hours and the occurrence of heavy rainfall, particularly during the summer months in China, highlighting how urbanization and human activities exacerbate this phenomenon [6][10][15]. Group 1: Rainfall Patterns and Timing - Statistical data from the China Meteorological Administration indicates that the peak intensity of summer rainfall in China occurs between 5 PM and 8 PM, coinciding with the end of the workday for many employees [6][12]. - Regions such as South China, Northeast China, North China, and the middle and lower reaches of the Yangtze River experience the highest rainfall during this time, particularly short-duration heavy rain lasting 1-3 hours [6][9]. Group 2: Urban Heat Island Effect - The urban heat island effect contributes to higher temperatures in cities, which in turn increases the likelihood of heavy rainfall during the evening hours due to the accumulation of heat and humidity [10][14]. - The presence of large buildings in urban areas retains heat, creating a "thermal blanket" effect that raises local temperatures significantly above surrounding areas [10][14]. Group 3: Impact of Urbanization - Rapid urbanization has led to a doubling of extreme hourly rainfall rates in regions like the Pearl River Delta since 1994, compared to the period before urbanization began [13][16]. - The frequency of extreme rainfall events has increased in urban areas compared to surrounding rural regions, indicating a direct correlation between urbanization levels and rainfall intensity [13][18]. Group 4: Human Activities and Pollution - Human activities during weekdays, such as increased vehicular traffic and industrial operations, intensify the urban heat island effect and contribute to higher pollution levels, which are linked to increased thunderstorm activity [15][19]. - Air pollution can alter rainfall patterns by affecting cloud formation and precipitation processes, leading to more intense and severe thunderstorms [16][19].