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1991-2020 Climatological Normals for Hong Kong

4 February 2021

Stepping into 2021, the Hong Kong Observatory compiled a new set of 30-year climatological normals for Hong Kong based on the meteorological data measured at the Hong Kong Observatory Headquarters and other key meteorological stations in the period from 1991 to 2020. The update of the climatological normals from the previous period of 1981-2010 to 1991-2020 is in accordance with relevant guidelines of the World Meteorological Organization in 2017[1], which recommended meteorological organizations updating these normals every 10 years.

Climatological normals have a wide range of uses, providing references on the recent climate for planning, design and applications in various sectors, such as agriculture, energy, engineering, water management, transportation, tourism, environment, and research. Normals are also used as references for climate monitoring and forecasting and serve as benchmarks for determining the anomaly of the current weather condition from the corresponding long-term average.

Members of the public can get access to information on the climatological normals for 1991-2020 at the Observatory's "Climatological Information Webpage" ( Information on previous normals for 1961-1990, 1971-2000 and 1981-2010 are also available at the same webpage for reference.

The comparison between the 1991-2020 and 1981-2010 normals reveals that there are statistically significant increases in the annual mean, mean maximum, and mean minimum temperatures in Hong Kong. This is commensurate with the significant long-term warming trend in Hong Kong[2] due to global warming and local urbanization. For annual rainfall and relatively humidity, the changes between these two 30-year periods are not statistically significant.

Comparison of the 1991-2020 and 1981-2010 normals
Meteorological element1991-2020
(“1991-2020” – “1981-2010”)
Annual Mean Temperature (oC)23.523.30.2*
Annual Mean Maximum  Temperature (oC)*
Annual Mean Minimum  Temperature (oC)21.621.40.2*
Annual Rainfall (mm)2,431.22,398.532.7
Annual Mean Relative Humidity (%)78780
*Changes are statistically significant

[1] WMO, 2017 : WMO Guidelines on the Calculation of Climate Normals, WMO-No. 1203.
[2] Climate Change in Hong Kong :