The Hong Kong Observatory (HKO) has been conducting meteorological observations since 1884 except for the Second World War during 1940-1946. The HKO possesses more than 130 years of meteorological observation records which are important references for climate change researches in Hong Kong.

(a)Temperature rise

Fig 3.1 shows a long-term ascending trend of the annual average temperature in Hong Kong. For the past hundred years, the annual average temperature increased at a rate of about 0.12°C per decade. The increase has become more significant in the later half of the 20^th century.

(b)More very hot days but fewer cold days

The number of hot nights (with a daily minimum temperature of 28°C or above) and very hot days (with a daily maximum temperature of 33°C or above) have increased by about 35 times and 6 times respectively over the last hundred years or so. On the contrary, the number of cold days (with a daily minimum temperature of 12°C or below) has decreased.

(c)More frequent extreme rainfall

Extreme rainfall events have become more frequent. The hourly rainfall record at the HKO Headquarters was usually broken once per decade in the past, but it was repeatedly broken in recent decades. The latest record of the highest hourly rainfall at the HKO Headquarters was 145.5mm in 2008. A more sophisticated analysis shows that the chance of an extreme rainfall event with hourly rainfall of 100 mm or more has doubled over the last century.

(d)Sea level rise

Tide gauge records in Victoria Harbour since 1954 indicated an obvious rise of the mean sea level. On average, the mean sea level in Victoria Harbour rose at a rate of about 31 mm per decade in the past 60 years or so.