The latest on climate change in Hong Kong

T C Lee

HKCCFProgramme on climate change

21 September 2010

CONTENT

• Background

• Observed changes- Temperature- Rainfall- Sea Level- Severe Weather Events- Other Meteorological Elements

• 21st century projections

• Future research activities

Climate Monitoring in Hong Kong

Hong Kong Observatory Headquarters

Regular meteorological observations commenced in 1884, including temperature, rainfall, pressure, sunshine duration (upto1960), wind speed/direction, etc.

King’s Park Meteorological Station

Daily radiosonde ascents began in 1951.

One of the stations in the Global Climate Observing System (GCOS) Upper Air Network (GUAN).

Other meteorological measurements since 1950s include pressure, temperature, rainfall, sunshine duration, evaporation, etc.

WGL

KPHKO

Lantau Island

Kowloon

HK Island

Locations of Key Climatological Stations in Hong Kong

Urban snapshots in Hong Kong

Dense development

Many Skyscrapers100 - 400m

e.g.IFC ~ 415 mCentral Plaza ~ 374m

Urbanization effect on temperature

Urbanization effect on wind speed, visibility and evaporation

Climate change in HK = Global Warming + Local Urbanization Effect

Observed Climate Change in Hong Kong

Element Trend

Average Temperature Increase

Annual Rainfall Increase

Mean Sea Level Increase

Temperature

Temperature trend in Hong Kong

Annual mean temperature recorded at the Hong Kong Observatory Headquarters (1885-2009). Data are not available from 1940 to 1946

Annual mean surface air temperature for 1951-2007 in Hongkong (red) andGuangzhou (green) as well as Macao (blue)

每十年上升0.17oC

+0.17oC/decade每十年上升0.10oC

+0.10oC/decade

每十年上升0.19oC

+0.19oC/decade

20

21

22

23

24

25

1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001 2006

Year 年

An

nu

al M

ea

n T

em

pe

ratu

re 年

平均

氣溫

(o

C)

Macao 澳門 Hong Kong 香港 Guangzhou 廣州

(Source : 冯瑞权 吴池胜 王安宇 何夏江 王婷 梁嘉静 黎婉文 梁必骐 , 1901—2007年澳门地面气温变化的分析 , 《气候变化研究进展 》 2009 年 01 期 )

1975-1980 2001-2006

(Source : 广东气候变化评估报告（节选） , 广东省气候变化评估报告编制课题组 ,广东气象 , Vol. 29 (3), 2007.)

Changes in average temperatures in Guangdong

Annual Number of Hot Night in Hong Kong (1885-2009)(Daily Min. Temp >= 28oC)

Annual number of cold days in Hong Kong (1885-2009) (Daily Min. Temp <= 12oC)

Annual number of very hot days in Hong Kong (1885-2009) (Daily Max. Temp >= 33oC)

Element Return period in 1900 Return period in 2000

Minimum Temperature ≤ 4oC

6 years 163 years

Maximum Temperature ≥ 35oC

32 years 4.5 years

Time dependent return period analysis of extreme temperature events in Hong Kong

(Source : Wong, M.C. and H.Y. Mok, 2009: Trends in Hong Kong Climate Parameters Relevant to Engineering Design. HKIE Civil Division Conference 2009 : Conference on Engineers' Responses to Climate Change.)

Rainfall

Rainfall trend in Hong Kong

Annual rainfall recorded at the Hong Kong Observatory Headquarters (1885-2009).Data are not available from 1940 to 1946

Number of rain days in Hong Kong (daily rainfall >=1 mm)(at HKO Headquarters)

60

70

80

90

100

110

120

130

140

150

1885 1895 1905 1915 1925 1935 1945 1955 1965 1975 1985 1995 2005Year

Nu

mbe

r of

Rai

nda

ys (

day

)

-1.1 day/decade

i.e. +3 days in a century

Number of heavy rain days (hourly rainfall > 30 mm) at Hong Kong Observatory Headquarters (1885 – 2009)

Record high hourly rainfall at the Hong Kong Observatory Headquarters (1885 – 2009)

ElementReturn period

in 1900Return period

in 2000

1 hour rainfall > 100 mm 37 years 18 years

2 hour rainfall > 150 mm 32 years 14 years

3 hour rainfall > 200 mm 41 years 21 years

Changes in frequency of extreme rainfall events based on time-dependent return period analysis

Extremes becoming more frequent

Long term trend of annual total rainfall due to heavy rainfall events (R95p)

Trend = + 21 mm per decade

Significant at 5 % level

0

200

400

600

800

1000

1200

1400

1600

1800

1884 1904 1924 1944 1964 1984 2004

Year

R9

5p

(m

m)

R95p : annual total rainfall at HKO Headquarters due to events exceeding the daily 95th percentile of the climatological normal (1971-2000)

Mean Sea Level

Sea Level Rise in Hong KongSea level rise in Hong Kong

On average, the mean sea level in the Victoria Harbour has risen at a rate of 2.6 mm per year during the period 1954 to 2009

Causes of Sea-level Change

Image source: Causes of sea level rise from climate change. (2002). In UNEP/GRID-Arendal Maps and Graphics Library. Retrieved March 11, 2010 from http://maps.grida.no/go/graphic/causes-of-sea-level-rise-from-climate-change.

Severe Weather Events

Number of Thunderstorm Days from 1947 to 2009(as observed at HKO Headquarters)

Annual number of tropical cyclones making landfall along the south China coast within 300 km of Hong Kong from 1961 to 2009

Annual number of typhoon making landfall along the south China coast within 300 km of Hong Kong from 1961 to 2009

0

1

2

3

4

5

6

1961 1966 1971 1976 1981 1986 1991 1996 2001 2006Year

Nu

mb

er o

f ty

ph

oo

n l

and

fall

wit

hin

300

km f

rom

Ho

ng

Ko

ng

Other Meteorological Elements

Annual mean daily solar radiation recorded at King’s Park Station (1958-2009)

Annual average of 12-hr 10 minute mean wind speed at King’s Park and Waglan Island (1968-2008)

Annual total number of hours with visibility at HKO Headquarters below 8km from 1968-2008

(relative humidity below 95% and not counting rain, mist or fog)

Projections for Hong Kong in the 21st century

Temperature : the increasing trend will continue. The mean temperature in the decade 2090-2099 is expected to rise by 4 to 5 oC relative to the period 1980-1999.

Rainfall : will increase during the latter half of the 21st century with about 10% increase relative to the 1980-1999 average.

Sea level : The sea-level at the South China Sea including Hong Kong is likely to be close to the global average in the long run. • According to IPCC AR4, the global average sea-level will rise by 0.18 to 0.59 m at

the end of 21st century relative to the period 1980 to 1999. • Recent studies by some research groups suggest higher projections

Uncertainties : there are still large uncertainties in the model simulation for the future climate, depending very much on the future forcing emission scenarios and local urbanization effect as well as the model characteristics/performance.

Magnitude of Extreme Sea-levels

Extreme sea-levels (mCD) at Victoria HarbourReturn period (year)

Extreme sea-level based on past data

Extreme sea-level after a mean sea-level rise of 0.59 m

Extreme sea-level after a mean sea-level rise of 1.4 m

2 2.9 3.5 4.3

5 3.1 3.7 4.5

10 3.3 3.8 4.7

20 3.4 4.0 4.8

50 3.5 4.1 4.9

Note: mCD = metres above Chart Datum.Chart Datum is 0.146 metre below Principal Datum.

A sea-level of 3.5 mCD similar to that during Typhoon Hagupit, a once in 50 years event,

would become a bienniel event after a rise of the mean sea-level by 0.59 m.

A sea-level of 3.5 mCD similar to that during Typhoon Hagupit, a once in 50 years event,

would become a bienniel event after a rise of the mean sea-level by 0.59 m.

Future Work on Climate Research

• Future trends of extreme temperature and rainfall events based on IPCC AR4 (daily model data)

• Update projections of Hong Kong climate in the 21st Century base on IPCC AR5 model data

• Urbanization effects on Hong Kong climate

• Weather and Health (Rotavirus, RSV, etc.) – collaboration with CUHK

• Climate and Ecosystem / Other social impacts

Summary

• Significant changes in the climate in Hong Kong were observed in the last century, including the increase in average temperatures and total rainfall as well as the rise of mean sea level.

• Studies of past occurrences of extreme temperature and rainfall in Hong Kong revealed that cold episodes have become rarer while very hot days and heavy rain events are becoming more frequent

• Looking into the future, Hong Kong can expect even warmer weather, more variable rainfall, and a sea level that keeps rising.

• Climate change research is an on-going process.

Thank You

Storm Surge + Sea-level Rise

Waves caused by Typhoon

Raised mean sea level

Coast Coast

Original mean sea level

After sea-level rise, storm surges will bring more frequent sea flooding to coastal low-lying areas.

What would happen in past storms?

Extreme sea-levels (mCD) at Victoria Harbour

TyphoonExtreme sea-level recorded

Extreme sea-level after a mean sea-level rise of 0.59 m

Extreme sea-level after a mean sea-level rise of 1.4 m

Wanda (1962) 3.96 4.55 5.36

Hagupit (2008) 3.53 4.12 4.93

Koppu (2009) 3.02 3.61 4.42

Note: mCD = metres above Chart Datum.Chart Datum is 0.146 metre below Principal Datum.

Possible inundation around the Pearl River Delta caused by a sea level rise

sea level rise of 0m sea level rise of 1m

(Source : Wong, K.M., K.H. Lau, J.P. Gray. (2007), Impact of sea level rise on Hong Kong and the Pearl River Delta, presented in International Conference on Climate Change, May 2007, Hong Kong.)

0

200

400

600

800

1000

1200

1400

1600

1970 1975 1980 1985 1990 1995 2000 2005 2010

Mon

thly

Ele

ctric

ity C

onsu

mpt

ion

per

Cap

ita (

MJ)

Domestic Electricity

Commercial Electricity

Year

1970-2009 Time Series of Seasonal Variation

Variation in electricity consumption in Hong Kong increases significantly in the last 4 decades in both domestic and commercial sectors.

Slope Correlation (r) P-value Significant at 5 %?2000's 2.97E+06 0.79 5.78E-14 Yes1990's 2.28E+06 0.64 4.86E-08 Yes1980's 1.11E+06 0.49 6.41E-05 Yes1970's 4.02E+05 0.37 1.02E-03 Yes

Monthly Electricity vs Monthly Cooling Degree-days (2000-2009)

y = 3E+06x + 4E+08

R2 = 0.6315

0.0E+00

1.0E+08

2.0E+08

3.0E+08

4.0E+08

5.0E+08

6.0E+08

7.0E+08

8.0E+08

9.0E+08

0 20 40 60 80 100 120

Monthly CDD (May-Oct)

Mo

nth

ly E

lect

rici

ty (

pe

r ca

pita

)

Monthly Electricity vs Monthly Cooling Degree-days (1990-1999)

y = 2E+06x + 3E+08

R2 = 0.404

0.0E+00

1.0E+08

2.0E+08

3.0E+08

4.0E+08

5.0E+08

6.0E+08

7.0E+08

8.0E+08

9.0E+08

0 20 40 60 80 100 120

Monthly CDD (May-Oct)

Mo

nth

ly E

lect

rici

ty (

pe

r ca

pita

)

Monthly Electricity vs Monthly Cooling Degree-days (1980-1989)

y = 1E+06x + 2E+08

R2 = 0.2426

0.0E+00

1.0E+08

2.0E+08

3.0E+08

4.0E+08

5.0E+08

6.0E+08

7.0E+08

8.0E+08

9.0E+08

0 20 40 60 80 100 120

Monthly CDD (May-Oct)

Mo

nth

ly E

lect

rici

ty (

pe

r ca

pita

)

Monthly Electricity vs Monthly Cooling Degree-days (1970-1979)

y = 402087x + 1E+08

R2 = 0.1372

0.0E+00

1.0E+08

2.0E+08

3.0E+08

4.0E+08

5.0E+08

6.0E+08

7.0E+08

8.0E+08

9.0E+08

0 20 40 60 80 100 120

Monthly CDD (May-Oct)

Mo

nth

ly E

lect

rici

ty (

pe

r ca

pita

)

During warm months (May-Oct) – Electricity Consumption vs CDD

Sensitivity of electricity use to climate factor increases in recent decades.

2000’s 1990’s

1970’s1980’s

A. Domestic Sector

Correlation is significant at 5% in all 4 decades.

Past and projected annual mean temperature anomaly for Hong Kong(based on IPCC AR4 annual mean projection data)

Past and projected changes in annual rainfall for Hong Kong