In the 65-year period after the World War II, the annual total rainfall at the Hong Kong Observatory Headquarters has been rising at a rate of 36 mm/decade, though not statistically significant at 5% level. The annual rainfall trend is small when compared to the year-to-year fluctuation.

Annual rainfall at the Hong Kong Observatory Headquarters (1947-2011)

The rainfall over different regions of Hong Kong was generally on a rising trend. The rate was higher in the urban areas than the New Territories, offshore islands and high grounds. Urbanization is one of the possible causes for the rainfall's increasing trend and the regional variation in Hong Kong. The higher temperature in urban areas enhances convective activities and the increase in concentration of suspended particulates from urban activities favours the formation and development of rain-bearing clouds.