An Overview on the past and predicted Climate Change in Hong Kong

WORKSHOP ON ASIAN CLIMATE CHANGE AND VARIABILITY:TRENDS AND POLICY

22 July 2011

H Y MokHong Kong Observatory

Climate change monitoring in Hong KongHong Kong Observatory Headquarters

Regular meteorological observations commenced in 1884, except during WW II

Kings Park Meteorological Station

Climate and upper-air station since 1951

Ta Kwu Ling Automatic Weather Station

Rural weather station since 1985*

The meteorological coverage of Hong Kong was further enhanced with the establishment of an automatic weather station network since the mid-1980s. Coverage of Monitoring NetworkHong Kong ObservatoryKings ParkTa Kwu Ling AWS*

Climate change in HK = Global Warming + Local Urbanization Effect Observed Climate Change in Hong Kong

ElementTrendAverage TemperatureIncreaseAnnual RainfallIncreaseMean Sea LevelIncrease

Year1970-2009 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.

Comparison between average temperature changes in China and in the Globe in the past 140 yearsLand surface global average temperature change and the average in China (relative to 1961-1990)

Spatial distribution of temperature changesover China during the past 50 years( NCC / CMA )Cooling WarmingMost regions turned to warmer, particularly in northern China

Temperature trend in Hong KongAnnual mean temperature recorded at the Hong Kong Observatory Headquarters (1885-2010). 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)(Source : , 19012007, 200901)

Annual number of very hot days in Hong Kong (1885-2010) (Daily Max. Temp >= 33oC)

Annual Number of Hot Night in Hong Kong (1885-2010) (Daily Min. Temp >= 28oC)

Annual number of cold days in Hong Kong (1885-2010) (Daily Min. Temp

Time dependent return period analysis of extreme temperature events in Hong Kong(Source :M. C. Wong, H. Y. Mok, T. C. Lee (2010), Observed changes in extreme weather indices in Hong KongInternational Journal of Climatology, published online on 27 October 2010)*

ElementReturn period in 1900Return period in 2000Minimum Temperature 4oC 6 years163 yearsMaximum Temperature 35oC32 years4.5 years

Spatial distribution of precipitation changesover China during the past 50 years( NCC / CMA )Decreasing IncreasingMore precipitation in western and southern, and much less in the North and northeast of China Ren et al., 2005

Rainfall trend in Hong KongAnnual rainfall recorded at the Hong Kong Observatory Headquarters (1885-2010). Data are not available from 1940 to 1946

Number of rain days in Hong Kong (daily rainfall >=1 mm)(at HKO Headquarters, 1885-2010)*

i.e. +0.2 days in a centuryNumber of heavy rain days (hourly rainfall > 30 mm) at Hong Kong Observatory Headquarters (1885 2010)*

Annual maximum 1-hourly rainfall at the Hong Kong Observatory Headquarters (1885 2009)

Changes in frequency of extreme rainfall events based on time-dependent return period analysis (GEV analysis)Extremes rainfall becoming more frequent(Source :M. C. Wong, H. Y. Mok, T. C. Lee (2010), Observed changes in extreme weather indices in Hong KongInternational Journal of Climatology, published online on 27 October 2010)*

ElementReturn period in 1900Return period in 2000 1 hour rainfall > 100 mm37 years 18 years 2 hour rainfall > 150 mm32 years14 years 3 hour rainfall > 200 mm 41 years21 years

Summary of the long term trend of extreme rainfall events in Hong KongThere is an increasing trend for both the intensity and frequency of short-term heavy rain events in terms of 1- to 3-hourly rainfall.

Contribution of heavy rain to the yearly total rainfall has increased with time.

Longest period with no or insignificant rain also increased with time.

Message: Its harder to rain. But if it rains, it pours.

Time series of the annual number of tropical cyclones of any intensitypassing within 100, 200 and 300 km of Hong Kong (1961-2008)

Time series of the annual number of typhoons passing within100, 200 and 300 km of Hong Kong (1961-2008)

Projections in the 21st century

Projected Temperature in China ensemble from 17 GCMsChina

Past and projected annual mean temperature anomaly for Hong Kong (relative to the average of 1980-99) Low-end - low GHG emission scenario and frozen urbanizationHigh-end - high GHG emission scenario and continued urbanization Middle-of-the-road - average of the GHG emission scenarios as well as of the two situations regarding urbanization Average temperature will continue to increase More very hot days and less cold days

Projections for annual number of hot nights, annual number of very hot days and annual number of cold days in Hong Kong (Result of 2010 study)

1980-1999Average for 1980-1999(Observation)2090-2099Projections for 2090-2099Low-endMeanHigh-endAnnual number of hot nights1687137175Annual number of very hot days92989131Annual number of cold days17015

Projected Precipitation in Chinaensemble from 17 GCMsChina

SRES A1B scenarioSpatial distribution of projected trend of dryness/wetness in China during 2000-2050

SRES A2 scenarioSpatial distribution of projected trend of dryness/wetness in China during 2000-2050

SRES B1 scenarioSpatial distribution of projected trend of dryness/wetness in China during 2000-2050

Past and projected changes in annual rainfall for Hong KongThe average annual rainfall recorded at the Hong Kong Observatory Headquarters will reach 2572 mm, 248 mm (11%) higher than the 1980-1999 average of 2324 mm. (Source : Lee, T.C., W.H. Leung and E.W.L. Ginn, 2008: Rainfall Projections for Hong Kong based on the IPCC Fourth Assessment Report. Bull. HK Met. Soc., 18, 12-22)

Projected occurrence of extremes (rainfall)Increase in extremely dry years from 2 in 20th century to 4 in 21st centuryIncrease in extremely wet years from 2 in 20th century to 10 in 21st century

Extreme rainfall projection study in 2011

Projection of extreme rainfall using daily temporal resolution global climate model data of AR4

Daily multiple (global) model data from Program for Climate Model Diagnosis and Intercomparison (PCMDI) website

Extreme indices projections and GEV analysis of daily rainfall

Timeframe:to be completed in 2011

Preliminary result: Annual number of rain day is expected to dropAnnual number of days with heavy rainfall (daily rainfall >= 100 mm) would increaseMore uneven distribution of wet and dry periods

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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 and more variable rainfall.

Key Vulnerable Areas in Hong KongThe consultancy study has identified eight key sectors as having high vulnerability to climate change impacts, namely:

Biodiversity and Nature Conservation;Built Environment and Infrastructure;Business and Industry;Energy Supply;Financial Services;Food Resources;Human Health; andWater Resources.

*Adaptation Options and MeasuresThe consultancy study proposes adopting the following framework to develop specific options for adapting to climate change:

MonitoringInstitutional strengthening and capacity buildingDisaster management and emergency planningResearch and investigationEducation and public awareness

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