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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 - PowerPoint PPT Presentation
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Drought Monitoring in Hong Kong using Standardized Precipitation Index (SPI)
MC Wu KW LiHong 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 3343mm (1997)
Lowest 901mm (1963)
Water Resources • Building Reservoirs – Plover Cove (1968), High
Island (1978)• Importing water from Dongjiang River in
Guangdong province Year Volume of importing water from
Dongjiang River (billion cubic meters per year)
1960 0.227
1964 0.68
1976 1.09
1982 2.2
2012 8.2
Allocation of Dongjiang Water
Currently, around 80% of Hong Kong’s total fresh water demand are supplied by Dongjiang water
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
Types of Drought
Meteorological
Temporal ScaleShort Long
Spatial Scale
Fine
Broad
Agricultural
Hydrological
Meteorological drought - measured the amount of dryness and the duration of dry period
Agricultural drought - based on the impacts to agriculture
Hydrological drought - refers to impacts on water supply
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
WMO Recommendation
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)
Precipitation (mm)
Cu
mu
lati
ve P
rob
abili
ty
SPI
1.0
0.8
0.6
0.4
0.2
0.0
0 20 40 60 80 100 -3 -2 -1 0 1 2 3
1.0
0.8
0.6
0.4
0.2
0.0
Normal~(0,1)
SPI classification
SPI values Category
+2.0 and above Extremely wet
+1.50 to +1.99 Very wet
+1.0 to +1.49 Moderately wet
-0.99 to +0.99 Near normal
-1.0 to -1.49 Moderately dry
-1.50 to -1.99 Severely dry
-2.0 and less Extremely dry
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
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 longterm ppt patterns
• 24-month SPI (SPI-24)– Characterizes persistent drought
SPI for monitoring persistent droughts in Hong Kong
SPI-24Extremely wet
Extremely dry
Characteristics of a drought eventSP
I
-1.0
(i) Minimum SPI ≤ -1.0 (ii) Duration: starts from SPI falling below zero and ends with SPI rising to zero(iii) Magnitude: the accumulated SPI between the drought duration (iv) Intensity = Magnitude / Duration
Duration
Magnitude (area)
0
Time
1 2 3
4 5 67
8
9
11
10
12
13
1415
16 1718
Drought episodes in HK based on SPI-24
1963
196206-196508(39 months)
189509-190306(94 months)
The 18 episodes in Hong Kong between 1885 and 2012
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
Thank you for your attention!