For temperature projection, as urbanization is an additional contributor to the rising temperature of cities, the study also takes into account the urbanization effect in Hong Kong. In the lower-bound situation, the level of urbanization is frozen; in the upper-bound situation, urbanization effect grows at a constant rate. In the following, three sets of results are presented and labeled as:

(a) "middle-of-the-road" - average of the scenarios as well as of the two situations regarding urbanization;
(b) "low-end" - low emission scenario and frozen urbanization;
(c) "high-end" - high emission scenario and continued urbanization.

Compared with the 1980-1999 average of 23.1 ℃, the annual mean temperature in Hong Kong in the decade 2090-2099 is expected to rise by 4.8 ℃ according to the middle-of-the-road projection. The corresponding low-end and high-end values are 3.0 and 6.8 ℃ respectively.

As for extreme weather, the study shows that the annual number of hot nights (days with a minimum temperature of 28 ℃ or above) and very hot days (days with a maximum temperature of 33 ℃ or above) in summer will increase. On the other hand, the annual number of cold days in winter (days with a minimum temperature of 12 ℃or below) will continue to drop.

The annual number of hot nights in summer is expected to increase from the average of 15 nights in 1980-1999 to 41 nights in 2090-2099 (middle-of-the-road projection). The corresponding low-end and high-end estimates are 30 and 54 nights respectively.

The annual number of very hot days in summer is expected to increase from the 1980-1999 average of 7 days to 15 days in 2090-2099 (middle-of-the-road projection). The corresponding low-end and high-end estimates are 12 and 19 days respectively.

The average annual number of cold days in winter is expected to drop below one in the decade 2030-39 (middle-of-the-road projection). The corresponding low-end and high-end estimates are 2040-2049 and 2020-2029 respectively. The average annual number of cold days at the end of the last century (1980-1999) was 14 days.

Details of the study on the temperature projections for Hong Kong in the 21st Century can be found in the paper "Temperature Projections for Hong Kong Based on IPCC Fourth Assessment Report".

Under the influence of global warming, annual rainfall in Hong Kong would increase at a rate of about 1% per decade in the 21st century, about the same rate as in the past 120 years. This trend is in line with the fact that as the hydrological cycle intensifies in a warmer world, global average precipitation would increase in the 21st century.

Under the anticipated increasing rainfall trend, in the last 10 years of this century, that is, in the years 2090 to 2099, the average annual rainfall at the Hong Kong Observatory Headquarters would be about 2430 mm, or 216 mm more than the 1961-1990 average of 2214 mm.

Apart from the overall upward trend, the year-to-year variability in rainfall would also increase in the 21st century. In the past 120 years, the highest annual rainfall recorded at the Hong Kong Observatory Headquarters was 3343 mm. In the 21st century, it is expected that there would be 6 years with annual rainfall above this figure. Likewise, in the past 120 years, the lowest annual rainfall recorded at the Hong Kong Observatory Headquarters was 901 mm. It is expected to see 3 years with annual rainfall less than this figure in the 21st century. The highest annual rainfall of 3343 mm was recorded in 1997, a year in which rainstorms triggered severe flooding and numerous landslides in Hong Kong. The Red and Black rainstorm warnings had to be issued on many occasions. The lowest annual rainfall of 901 mm was recorded in 1963. Water rationing was implemented that year, with water supplied to the public once every four days.

In the 21st century, the number of days with heavy rain is also likely to increase. From the 30-year period 1961-1990 to the last 30 years of this century, that is 2070-2099, the number of days in a year with hourly rainfall exceeding 30 mm (the rainfall criterion for issuing the Amber Rainstorm Warning) will increase from five and a half to six and a half.

Results of the study on the rainfall projections for Hong Kong in the 21st Century can be found in the press release announced on 26 August 2005 and the paper “Projected Change in Hong Kong's rainfall in the 21st century” published in the Bulletin of Hong Kong Meteorological Society.