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Drought Monitoring in Hong Kong using Standardized Precipitation Index (SPI)

Drought Monitoring in Hong Kong using Standardized Precipitation Index (SPI). MC Wu KW Li Hong Kong Observatory. Historical Droughts in Hong Kong. Serious droughts in 1963 & 1967 Water restriction - supply in 4 hours every 4 days. Rainfall in Hong Kong. Average 2399 mm Highest

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Drought Monitoring in Hong Kong using Standardized Precipitation Index (SPI)

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  1. Drought Monitoring in Hong Kong using Standardized Precipitation Index (SPI) MC Wu KW Li Hong Kong Observatory

  2. Historical Droughts in Hong Kong • Serious droughts in 1963 & 1967 • Water restriction - supply in 4 hours every 4 days

  3. Rainfall in Hong Kong Average 2399 mm Highest 3343mm (1997) Lowest 901mm (1963)

  4. Water Resources • Building Reservoirs – Plover Cove (1968), High Island (1978) • Importing water from Dongjiang River in Guangdong province

  5. Allocation of Dongjiang Water Currently, around 80% of Hong Kong’s total fresh water demand are supplied by Dongjiang water

  6. What is Drought? • Different perceptions for different people living in different climate zones • Sahara desert: less than 10 mm / year • Cherrapunji (northeast of India): more than 10000 mm / year • Three main types based on its impacts on different aspects: • Meteorological drought • Agriculture drought • Hydrological drought

  7. Types of Drought Temporal Scale Short Long Meteorological drought - measured the amount of dryness and the duration of dry period Fine Meteorological Agricultural Spatial Scale Agricultural drought - based on the impacts to agriculture Hydrological Broad Hydrological drought - refers to impacts on water supply

  8. WMO Recommendation Standardized Precipitation Index (SPI) should be used as a universal meteorological drought index for more effective drought monitoring and climate risk management (2009) A user guide on SPI was issued in 2012

  9. SPI - a probability index • Based on the cumulative probability of rainfall amount for any time scale • Fitted to a gamma distribution • Transformed into standard normal (mean = 0 and s.d. = 1) Normal~(0,1) 1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 Cumulative Probability -3 -2 -1 0 1 2 3 0 20 40 60 80 100 Precipitation (mm) SPI

  10. SPI classification

  11. Advantages of SPI • Simple – only rainfall is required as input parameter • Normalized – can be used to compare the drought severity for areas with different climates • Various time scale – can be used to assess different types of drought or for different planning purposes

  12. SPI in different time scales • 3-month SPI (SPI-3) • Provides information on short term and seasonal variation in ppt • 6-month SPI (SPI-6) • Characterizes medium-term trends in ppt • 12-month SPI (SPI-12) • Reflects the longtermppt patterns • 24-month SPI (SPI-24) • Characterizes persistent drought

  13. SPI for monitoring persistent droughts in Hong Kong SPI-24 Extremely wet Extremely dry

  14. Characteristics of a drought event • Minimum SPI ≤ -1.0 • Duration: starts from SPI falling below zero and ends with SPI rising to zero • Magnitude: the accumulated SPI between the drought duration • Intensity = Magnitude / Duration Duration 0 SPI -1.0 Magnitude (area) Time

  15. Drought episodes in HK based on SPI-24 189509-190306 (94 months) 196206-196508 (39 months) 13 4 5 6 17 16 10 9 7 18 1 3 14 2 12 8 15 11 1963

  16. The 18 episodes in Hong Kong between 1885 and 2012

  17. SPI-24 for Heyuan 新豐江水庫Xinfengjiang Reservoir 河源Heyuan 東江Dongjiang SPI-24 for Hong Kong 香港 Hong Kong

  18. Collaboration • SPI-24 for HK as well as the cities in Dongjiang River Basin such as Heyuen can provide useful reference information for the future management and planning of water resources in Hong Kong • Hong Kong Observatory is collaborating with the Water Supplies Department in utilizing climate information and products for drought monitoring and water resource management

  19. Thank you for your attention!

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