The latest on climate change in Hong Kong

The latest on climate change in Hong Kong T C Lee HKCCF Programme on climate change 21 September 2010

CONTENT • Background • - Observed changes Temperature Rainfall Sea Level Severe Weather Events Other Meteorological Elements • 21 st century projections • Future research activities

Climate Monitoring in Hong Kong Observatory Headquarters Regular meteorological observations commenced in 1884, including temperature, rainfall, pressure, sunshine duration (upto 1960), 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 1950 s include pressure, temperature, rainfall, sunshine duration, evaporation, etc.

Locations of Key Climatological Stations in Hong Kowloon KP HKO Lantau Island HK Island WGL

Urban snapshots in Hong Kong Dense development Many Skyscrapers 100 - 400 m e. g. IFC ~ 415 m Central Plaza ~ 374 m

Urbanization effect on temperature

Urbanization effect on wind speed, visibility and evaporation

Observed Climate Change in Hong Kong Climate change in HK = Global Warming + Local Urbanization Effect 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) and Guangzhou (green) as well as Macao (blue) (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)

Changes in average temperatures in Guangdong 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. )

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

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

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

Time dependent return period analysis of extreme temperature events in Hong Kong Element Return period in 1900 Return period in 2000 Minimum Temperature ≤ 4 o C 6 years 163 years Maximum Temperature ≥ 35 o. C 32 years 4. 5 years (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)

Number of heavy rain days (hourly rainfall > 30 mm) at Hong Kong Observatory Headquarters (1885 – 2009) i. e. +3 days in a century

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

Extremes becoming more frequent Changes in frequency of extreme rainfall events based on timedependent return period analysis Element Return period in 1900 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

Long term trend of annual total rainfall due to heavy rainfall events (R 95 p) R 95 p : annual total rainfall at HKO Headquarters due to events exceeding the daily 95 th percentile of the climatological normal (1971 -2000)

Mean Sea Level

Sea. Level level Rise rise in Sea 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

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 8 km from 1968 -2008 (relative humidity below 95% and not counting rain, mist or fog)

Projections for Hong Kong in the 21 st century Temperature : the increasing trend will continue. The mean temperature in the decade 2090 -2099 is expected to rise by 4 to 5 o. C relative to the period 19801999. Rainfall : will increase during the latter half of the 21 st 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 AR 4, the global average sea-level will rise by 0. 18 to 0. 59 m at the end of 21 st 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 (m. CD) at Victoria Harbour Return Extreme sea-level period level based after a mean sea(year) on past data level rise of 0. 59 m Extreme sea-level after a mean sealevel 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 50 3. 5 A sea-level of 3. 5 m. CD similar to that during Typhoon 50 years event, 4. 0 Hagupit, a once in 4. 8 would become a bienniel event after a rise of 0. 59 m. 4. 1 the mean sea-level by 4. 9 Note: m. CD = metres above Chart Datum is 0. 146 metre below Principal Datum.

Future Work on Climate Research • Future trends of extreme temperature and rainfall events based on IPCC AR 4 (daily model data) • Update projections of Hong Kong climate in the 21 st Century base on IPCC AR 5 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 Coast Original mean sea level Raised 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 (m. CD) at Victoria Harbour Typhoon Extreme sea-level after a mean sea- after a mean searecorded level rise of 0. 59 m 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: m. CD = metres above Chart Datum is 0. 146 metre below Principal Datum.

Possible inundation around the Pearl River Delta caused by a sea level rise of 0 m sea level rise of 1 m (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. )

Variation in electricity consumption in Hong Kong increases significantly in the last 4 decades in both domestic and commercial sectors. Year 1970 -2009 Time Series of Seasonal Variation

A. Domestic Sector During warm months (May-Oct) – Electricity Consumption vs CDD 2000’s 1990’s 1980’s 1970’s Correlation is significant at 5% in all 4 decades. Sensitivity of electricity use to climate factor increases in recent decades.

Past and projected annual mean temperature anomaly for Hong Kong (based on IPCC AR 4 annual mean projection data)

Past and projected changes in annual rainfall for Hong Kong