LCQ18: Provision of meteorological information by Hong Kong Observatory
Following is a written reply by the Secretary for Commerce and Economic Development, Mr Gregory So, to a question by the Hon Frederick Fung in the Legislative Council today (February 22):
Some members of the public have relayed to me that differences often exist between the temperatures recorded at the Hong Kong Observatory (HKO) Headquarters and those recorded at other weather stations in urban districts, and the temperatures recorded at the HKO Headquarters are not only unrepresentative but also fail to truly reflect the actual temperatures in most urban districts. For example, differences between the temperatures were as big as 2°C to 3°C during this Lunar New Year (January 22 to 29 this year). Moreover, at present, the latest weather report, the short-range weather forecast and the seven-day weather forecast announced by the HKO are all based on the data recorded at the HKO Headquarters. In this connection, will the Government inform this Council:
(a) of the respective differences between the daily highest and lowest temperatures recorded at various weather stations in urban districts (including Sham Shui Po, King's Park, Kowloon City, Wong Tai Sin, Kwun Tong and Happy Valley, etc.) and those recorded at the HKO Headquarters during this Lunar New Year; the biggest differences among the data on the lowest and highest temperatures collected at any one time; whether the HKO has looked into the reasons for the differences between the temperatures; whether the HKO has in the past examined the impact of the development of the vicinity of the HKO Headquarters on the collection of weather data; if so, of the result;
(b) given the differences between the temperatures recorded at the HKO Headquarters and those recorded at other weather stations in urban districts, whether the HKO has conducted studies to find out if there are also differences in other weather parameters (e.g. relative humidity and air pressure, etc.); given that at present, a number of district weather stations do not provide weather data other than those on temperature, whether the HKO will consider setting up other meteorological instruments in various district weather stations to record such data, so as to truly and comprehensively reflect the weather conditions in various districts; and
(c) whether the authorities will improve the existing practice of using the data of the HKO Headquarters as the basis for the latest weather report, the short-range weather forecast and the seven-day weather forecast (e.g. considering methods such as adopting average or weighted data, etc.), so as to reflect more truly the weather information of urban districts; if not, of the reasons for that?
Our response to the enquiries raised by the Hon Frederick Fung is as follows:
(a) and (c) The temperature readings recorded at weather stations in various urban districts from January 22 to 29 this year are given in Annexes I and II.
According to the observations and analysis of the HKO, not only would the weather data taken at different districts be affected by factors such as cloud dimension, wind speed and direction etc, the geographical location of the weather station and its surrounding environment (including the degree of urbanisation) might also have a bearing. The temperature measurements could well vary even within the urban areas.
Over the years, the HKO has been using the weather data prevailing at its Headquarters in Tsim Sha Tsui as the baseline for its weather reports and forecasts. This practice is well understood and widely accepted by the general public. The HKO has studied the impact of urban development on the weather data collected. It has caused a rise of less than 1°C in the average temperature recorded at the HKO's Headquarters in recent years. Nevertheless, the impact of urban development would similarly arise even if we were to use the data of a weather station in another urban district as the baseline. Nor would the use of alternative statistical methods (such as those adopting the average readings across different stations) necessarily result in more representative figures.
To meet public demands for district-specific weather information, the HKO disseminates weather data such as the temperature, relative humidity, wind speed and direction, etc recorded at individual weather stations throughout the territory via different channels (including the Internet website of the HKO, smart phone applications, the media and telephone enquiry service, etc). If the temperature in a certain region is expected to be different from that at its Headquarters by a relatively more significant margin, the HKO will so remind the public.
(b) The Hong Kong Observatory monitors weather conditions across Hong Kong through a network of over 30 weather stations. Most of these stations provide a range of regional weather information, including temperature, wind speed and direction, rainfall and relative humidity etc. The HKO will consider installing additional instruments at individual weather stations on a need basis. As regards the mean sea level pressure (air pressure), there is generally little variation from district to district. Nevertheless, information on air pressure from 12 weather stations is made available through the HKO's website for interested parties.