Gregorian/Lunar Calendar
Traditional Chinese Simplified Chinese
climate change

Climate Projections for Hong Kong

<<Temperature

Rainfall

Mean sea level>>

The Observatory utilizes data of a number of climate models in the IPCC Fifth Assessment Report (AR5) and statistical method to project the rainfall changes in Hong Kong in the 21st century. Under the high greenhouse gas concentration scenario (RCP8.5), the number of extremely wet years is expected to increase from three in 1885-2005 to about 12 in 2006-2100, which is roughly the same as the previous projection (IPCC Fourth Assessment Report AR4). The number of extremely dry years would remain about the same. Besides, the annual rainfall in late 21st century is expected to rise by about 180 mm when compared to the 1986-2005 average.

figure
Projected annual rainfall anomaly of Hong Kong relative to the average of 1986-2005 under the high (red) and medium-low (orange) greenhouse gas concentration scenarios (solid line plots the mean value while dashed lines show the likely range of projection results). Historical observations are shown in black.


Low
concentration scenario
Medium-low
concentration scenario
Medium-high
concentration scenario
High
concentration scenario
Future changes in extremely wet and extremely dry years under the high greenhouse gas concentration scenario

Future changes in extremely wet and extremely dry years under the high greenhouse gas concentration scenario

 

» Climate projections under different greenhouse gas concentration scenarios

 

Under the high greenhouse gas concentration scenario, the annual number of extreme rainfall days (daily rainfall ≥ 100 mm) would increase from an observed value of 4.2 during 1986-2005 to 5.1 by the end of this century (2091-2100). The average rainfall intensity (i.e. annual rainfall divided by the number of rain days), the annual maximum daily rainfall, the annual maximum 3-day rainfall and the annual maximum number of consecutive dry days would increase, while the annual number of rain days would decrease.

  1986-2005
Actual
2051-2060
Projection
2091-2100
Projection
2051-2060
Projection
2091-2100
Projection
Greenhouse gas concentration scenario -- Medium-low Medium-low High High
Annual number of extreme rainfall days 4.2 4.5 4.4 5.0 5.1
Average rainfall intensity (mm/day) 23.4 25.0 24.0 25.4 26.7
Annual maximum
daily rainfall (mm)
221 246 228 243 273
Annual maximum
3-day rainfall (mm)
367 482 454 476 523
Annual maximum number of consecutive dry days 46 49 52 54 59
Annual number of rain days 102 103 102 100 97

Projected annual number of extreme rainfall days, average rainfall intensity, annual maximum daily rainfall, annual maximum 3-day rainfall, annual maximum number of consecutive dry days and annual number of rain days.



Low
concentration scenario
Medium-low
concentration scenario
Medium-high
concentration scenario
High
concentration scenario
Projected annual maximum daily rainfall (mm) and annual maximum 3-day rainfall (mm) under the high greenhouse gas concentration scenario

Projected annual maximum daily rainfall (mm) and annual maximum 3-day rainfall (mm) under the high greenhouse gas concentration scenario


» Extreme rainfall projections under different greenhouse gas concentration scenarios

 

Note:

Climate projection uncertainties

It is important to note that climate projection is very different from weather or seasonal forecasts. Climate projection involves assumptions in future socio-economic and technological developments and greenhouse gas emission scenarios and aims at describing the plausible change in the future climate from a long-term perspective, rather than depicting the "day-to-day" or "year-to-year" variations in weather.

Although a majority of the model projections suggests in general consistent trends for the changes in the climate of the 21st century, inter-model differences in the projections for the future climate are still rather large. This, to a certain extent, reflects that climate projection is still subject to various uncertainties in the simulation of future climate, which depend very much on such factors as future greenhouse gas emissions, the choice of models, the ability of climate models to simulate physical processes, the downscaling methodology, the stability of the statistical downscaling relationship in the future. The technique is expected to continue to improve over time as scientists know more about various physical processes that impact on the climate.