An example of an intense rainfall event with 20mm/hr is London in July 2021, when 40mm of rain fell over three hours at Kew Gardens, flooding the underground and other infrastructure. https://www.metoffice.gov.uk/about-us/press-office/news/weather-and-climate/2023/new-research-shows-increas...
Observations of Our Changing Planet: Weather EXTREMES Professor Menglin Jin METR112: Global Climate Change The Weather Extremes and