Since the establishment in 1883 of the Royal Observatory Hong Kong (renamed Hong Kong Observatory after the handover), continuous records have been kept at the headquarters station in Tsim Sha Tsui, except from 1940 to 1946.
From 1884 to 2011, the mean annual rainfall at the station was 2,228 mm, ranging from 901.1 to 3,343 mm. The top 10 wet and dry years are indicated in the chart (right), which shows that eight of the wettest years occurred during the past 60. Five were strong El Nino years, with the two wettest years, 1997 and 1982, ranking the most intense and second-most intense respectively.
Satellite tracking of volcanic clouds has indicated that two wet years, 1982 and 2008, were connected to major volcanic events - the eruption of the El Chichon volcano in Mexico in March and April, 1982, and the Chaiten volcano in Chile in May 2008.
The El Chichon debris took 12 days to reach Hong Kong, contributing condensation nuclei for torrential rainfall in late April to May. Stratospheric warming of the tropics may have been responsible for the intense El Nino episode. In 2008, the Chaiten debris took 35 days to arrive, and caused the wettest June in Hong Kong's history, including the once-in-1,100 year rainstorm on June 7. Besides severe flooding in various locations, the intense rainstorm caused more than 1,600 landslides on Lantau Island.
The 10 driest years are relatively evenly distributed from 1898 to 2011. During 1963, Hong Kong's worst drought year, water supply was reduced to just four hours in over four days. The severe drought has been attributed to air circulation changes resulting from the March-May eruption of the Agung volcano on the Indonesian island of Bali.
The June 1991 eruption of the Pinatubo volcano in the Philippines was a factor in Hong Kong's 11th driest year on record.