1. Terrestrial observations
In Hong Kong, before the establishment of the Hong Kong Observatory (HKO) in 1883, regular meteorological observations (such as pressure, temperatures, rainfall and weather remarks) were collected since the 1850s. Starting in 1884, HKO has been regularly conducting various meteorological observations at the headquarters, apart from a break of the records from 1940 to 1946 owing to World War II. It is one of the World Meteorological Organization recognized Centennial Observing Stations (WMO station code: 45005) with over a century of continuous observations of essential surface meteorological observations. As part of HKO's wide range of climate services, HKO has also made available the more than 130 years of climate data together with a whole range of other climate information and statistics in its Climatological Information Services webpage (http://www.weather.gov.hk/cis/climat_e.htm) for the easy access by public and users in different sectors.
Besides meteorological observations at HKO, efforts have been made to recover the daily rainfall data at the Botanic Garden between 1892 and 1926 from the annual report of the Botanical and Afforestation Department and the weather observations from those weather log books of Gap Rock Lighthouse (a small island about 43 km to the southwest of Hong Kong) from 1919 to 1938 which is still available in HKO. With a view to narrowing the gap of missing data between 1940 and 1946, some of the daily and monthly temperature and rainfall records in Hong Kong were recovered from historical government reports and newspaper in 1940, 1941 and 1946.
2. Marine observations
For observations from the marine area, HKO started to recruit a fleet of locally based voluntary weather observing ships since 1949 under the Voluntary Observing Ships' Scheme of the then International Meteorological Organization (the predecessor of World Meteorological Organization). Prior to 1949, limited ship observations have been recovered from the extracts of ship observations, the Report of the Director of the Observatory, hand-written ship observations and marine publications.
3. Digitisation of Historical Data
Since 1970s, HKO has digitized most of the available hourly observations at its headquarters from 1884 to 1970. For the archival of pre-WWII historical weather charts, HKO has commenced a project to scan all available historical weather charts before 1939 into digital image formats. HKO also commenced a project to recover the historical hourly relative humidity data at the Headquarters from 1884 to 1960.