University of Bristol - Historical Photographs of China reference number: NA16-099. Image from an album in The National Archives referenced as ‘HONG KONG 3. Views of Hong Kong from the 1860s to the 1920s' (CO 1069-446). According to the Hong Kong Observatory, the highest record of daily rainfall ever recorded in Hong Kong, is 534.1 millimetres - the 19th July 1926 rainstorm. See https://www.hko.gov.hk/en/blog/00000135.htm. See NA16-100 (another photograph of the effects of the 1926 rainstorm on Pedder Street).
Flooding caused by the 19th July 1926 rainstorm, Pedder Street, Hong Kong
Black and white photograph
The National Archives, London